Bob Fritz knows his way around a home machine shop.

Why you need your own machine shop, and how to afford it.

I

’m not a machinist, and I don’t play one on TV. What I am, however, is a home machinist; I’m the guy who wants to cut a square hole through a pipe, or a long slot in a bit of flat steel…you know, the sort of job that would take a week and could cost the same as that new GPS you’ve been drooling over if you took it to the local machine shop. It’s the sort of job you could do if you just had a bit of skill and the right tools. What we’re going to cover is just that: a discussion of the tools (no, you don’t have to spend a fortune) and the skills (yes, even you, who sneered at the guys who took Industrial Arts classes in high school, can do this) that you’ll need to tackle these sorts of projects. So why go to all this trouble? For instance, why cut a square hole through a pipe? I recently found that the tubes that accept the gear legs on my Van’s Photos: Courtesy the Manufacturers, Bob Fritz

BY BOB FRITZ

RV-6 kit had been distorted by welding. To round them out I needed to run a ream through them. I called a couple of professional shops that I know and they said, “No, can’t set that up…don’t have a milling machine that big. Have to do it by hand.” Hmmm, that would be expensive! Well, first off, it’s a tube that should be 1.375-inch inside diameter. Yes, a ream that big is available and, no, it’s not expensive, only about $30. But what to turn it with? A big wrench won’t work; too much torque all applied to one side cocks the ream over and jams it. What’s needed is a tee handle! The ream has a round shank terminated by a square end, so I took a piece of pipe lying around the shop, set it up in the milling machine, drilled a round hole though one side

and then, using a small endmill, cut a square hole opposite the round. Voila, a tee handle. It worked too. That probably would have cost a couple hundred bucks

Fitting a round peg into a square hole. KITPLANES April 2007

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Home Machinist, Part 1 continued to have the experts do it, and it took less time for me to do it than to run it down to a shop.

Don’t You Just Love Justifying Toys? You’re still with me, so that must mean you’re thinking, “Hey, I needed to do something very much like that!” The question is where to start. First off, have some idea of how to use the equipment. This is supposed to be fun, and there’s nothing like fast progress to get you grinning. There are two ways of doing this: 1) Check if there’s a local high school or junior college that runs adult education classes in the evening. If they still have an Industrial Arts department you might find that you can go down there in the evenings with your projects and get both instructions and the machine tools; 2) Check out the web sites for howto. (A sampling of good sites is listed at the end of the story; direct links can be found at www.kitplanes.com.) Yes, it’s slower, but the longest journey begins with a single step, Grasshopper, and you’d be amazed how fast you’ll figure it out to the level you need. A community workshop would also be a great place to get your hands on the hardware. Or some of the manufacturers have videos and web pages with a lot of good information about how to get

started. I’d like to hear from readers who have suggestions about other sources of training. (Send them to editorial@kitplanes. com, and I’ll include them in future articles.) Just don’t be put off if you have zero experience; you didn’t have any experience in building an airplane and you took that on, right?

What About the Cost? Too expensive, you say? Well, let’s look at it this way: Your neighbor likes to fish, so he just bought a nice bass boat that needs a trailer and a new truck to pull it. The boat needs a new fish-finder/depth sonar, CD player, etc. Does $30-60,000 sound about right? That buys a lot of fish, and the boat depreciates about 30% a year! (The fish depreciate even faster.) But a nice machine shop can be set up for about 5% of the cost of the first year’s depreciation of this fishing rig. Perspective is everything. Not only is a shop a lot less money, that airplane you’re building gains in value

The Midas 1220LTD is an excellent choice.

when it gets the FAA sign-off. Anything you buy to aid that process is, in a very real financial sense, an investment. (Yes, I’m married. And, yes, she thinks this is a reasonable idea.) The really neat thing about owning your own machine shop is that it’s eminently useful after your Bugsmasher 8 is done. Next up is what to buy. You already are, or are thinking of, building an airplane, so presumably you have a pretty good toolbox with a dial-indicating caliper, maybe a nice little bandsaw, and you know the difference between a #2 and #3 Phillips screwdriver. If so, you’re a good candidate for a milling machine and/or a lathe. What’s the difference? Well, a mill holds the part (clamped down on a table or in a vise) and moves it in the horizontal axis while a spinning cutting tool is moved in the vertical axis. A lathe, on the other hand, usually spins the material about its own horizontal axis while moving the cutting tool in the two horizontal axes. That means a mill can cut

You get Timkin bearings and computer control for $13,000.

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a flat spot on the side of the material or knock a square hole through it, while a lathe can cut circumferential rings around a cylinder or drill a hole exactly on the material centerline.

Mill or Lathe, Then? Which is better? Experts can use a mill to do almost any job that can be done on a lathe, but not the other way around. The operative word here is “experts.” The other implied operative is convenience; if the operation is complex or requires an overly clever setup, then it’s not for you. If you know how to do it, then you’re already way beyond the scope of this article. You have a choice: Buy a lathe and then a mill, or buy a mill and then a lathe. Deciding comes down to an issue of floor space in the shop, beyond the fact that this is an investment. Each machine will take up about 15 square feet. In a two-car garage, that eats up open work area fast, but if you’ve got it, go for it. There’s a third option. If you don’t have the space, and assuming you can’t sell the spouse on converting the living room, then a combination machine might fill the bill. I started in a one-car garage with parts going to storage, so I was severely limited and could only consider a combination machine. It’s not capable of taking the bigger bits of raw material and, being lower cost, doesn’t have the precision of the machines at the local professional shop, but it uses only 9 square feet of floor space. Think of it this way. A 10-ton dump truck carries more than your car, but do you need that capacity? The biggest load you’d ever see is a couple of bags of cement. I’ve had times where I wanted bigger, faster, computer controlled, more accurate, etc., but for the sort of work I want to do, the combination machine is fine. Anything larger I take to the pros, and so far that hasn’t happened.

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Price of Admission For a combination machine, prices range from $500 to $13,000, and you get what you pay for. The low end is barely useful; the high end has every option includKITPLANES April 2007

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Home Machinist, Part 1 continued ing numeric control. You can target the $2500-$3500 range, however, and get a machine that is more than adequate for the typical home user. Now that you’ve decided it’s monetarily justified and you don’t have the space for separates (lucky you if you do), what to buy? There are several nice hobby machines out there, but what should you look for? Well, like the dump truck analogy, you could look at how you’ll use the

This tool post is inexpensive, but it is the best upgrade for the lathe.

This works, but it isn’t convenient when it comes time to change the lathe tool.

machine. But if you’re like me, you probably won’t have a crystal-clear set of jobs, so let’s run a check list of what to look for in a combination machine. Thread cutting. Most of the machines will advertise that they can cut threads, but in the four years I’ve had mine, I’ve yet to do any.

Ease of transfer. What you will want to do is switch from milling to lathe work with a minimum of fuss. If you have to switch belts or bolt/unbolt something other than a vise, then look elsewhere; it has to be convenient or it won’t get used. Ease of speed change. If it takes 10 minutes to change the tool speed, keep on looking for the same reason noted above. Size of raw stock. Here’s where you have to look at what you want to do versus what the machine will do. I’ll cover this in some detail next month, but bigger is better. All of the manufacturers advertise accessories, but are they any good? Do you need them, and if so, which ones? This can be confusing as well as tempting; after all, more is better, right? Not always. Don’t buy your machine based on the accessories, because once you start working you’ll find that what’s included ranges from useful to never used. Just take the package and plan on a few upgrades, most notably the vise and the tool post. Fortunately, the upgrades usually cost less than $100 and they’re well worth it. The single most important upgrade to the milling section is a good vise.

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Home Machinist, Part 1 continued

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Well, that’s a lot. We’ve touched on the cost, justification, use and a few of the basics to look for. In future articles we’ll evaluate combination machines and compare their capabilities. We’ll take you to bargain sources of accessories and make some recommendations. Later, we’ll talk about some projects specific to kit aircraft such as cutting a panel and some dandy little customizations to make your plane say “mine” not “just another kit.” As a home machinist, I’d like to hear from you pros out there. Send a note to our editorial email with the subject of “Home Machinist” if you have tips, updates, corrections or just want to point out a gaff. After all, it’s the journey not the destination that makes flying interesting. Editor’s note: This is the first of a monthly multi-part series on machining for the masses. If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

RESOURCES Department of Mechanical Engineering, Massachusetts Institute of Technology http://www.me.mit.edu/lectures/ machinetools/lathe/intro.html Tech Shop http://techshop.ws

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A piece of pipe became a ream handle and saved several hundred dollars.

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Comparing the options: the lathe section.

BY BOB FRITZ

“M

oney itself isn’t lost or made, it’s simply transferred from one perception to another.”—Oliver

Stone. There’s the rub. It’s all a matter of perception balanced by reality. Last month we figured out that a home machining center is a good investment. To recap, you’re going to spend some money on a hobby. Your neighbor just indulged his hobby when he decided to go bass fishing. He’s making payments on $30,000 worth of equipment that depreciates 30% the first year. As Bart Simpson would say, “Ay Caramba!” OK, call me wildly off the mark and cut that in half, but that’s what his hobby costs. Now, with that in mind, what do At first blush, this machine looks adequate, but my friend Hank says that although he’s used it to build three airplanes, he’d have been smart to “buy up.”

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The basic components of the combination machine. Keep this photo handy for future reference in identifying the parts.

Lathe bed travel to the left. If enough is OK, then more is better and too much is just right. Here’s the lathe bed at the far right. It doesn’t look like much, but the cost of the machine goes up drastically with greater travel.

you want to spend on your hobby? Your mama didn’t raise any fools, so you figure at that price you can go to the spouse and say you want to go fishing, look Photos: Bob Fritz and Courtesy the Manufacturers

down, kick the dirt a bit, and then settle for that new machining center at about one-third the price of the neighbor’s boat depreciation. You see, it’s not

the amount of money being spent that paralyzes us; it’s the perception of doing something out of the ordinary. That said, let’s move on to figuring out what to buy. You have a lot of choices, ranging from under $500 to over $13,000, but to be realistic about it, you should target about $2500 to $3500 to get a good, functional, easily converted combination machining center. If you want to look to the future, there are always accessories (think birthday and Christmas). Before you focus on the low end, let’s pop one more balloon. “Yeah, it ain’t much, but it’s OK for a beginner” is sophistry of the worst sort. Cogitate on this, Grasshopper: Try to teach someone to drive a car that has loose steering. The car wanders all over the road. Sure, you can keep it between the lines and watch for the hazards. But can they? Not a chance! A beginner needs the best possible equipment to compensate for a lack of skill. Now, don’t confuse quality with bells and whistles—’taint the same thing. What you’re looking for in the quality department are just three things: 1. Smooth motion of the things that should move. 2. Stability of the things that shouldn’t move. 3. Easy changes, be they converting from mill to lathe, changing rotational speeds, or changing the cutting tool. It should be as obvious as a pumpkin in a horse trough that you get what you pay for. The caveat, though, is that there will be a period of cleaning and adjusting when the machine arrives, so don’t think you’ll plug-and-play on day one. Now, with so many choices, how’s a newbie supposed to know what is needed? If all you’re doing is a daily commute, a beater Chevy is just as good as an Aston Martin (so long as the steering is tight!). With that in mind, let’s take a look at what’s available for you, the home machinist to be. KITPLANES May 2007

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Home Machinist, Part 2 continued

The swing over the bed. Here it’s 7 inches over the table and 12 inches over the bed.

For Openers Behind door number one we have the $500 machine. It usually has one motor, maybe three speeds on the lathe, a few more for the mill and a short bed so you can’t work on an item more than about 10 inches in the X direction. The milling head swings out of the way, but it cannot be raised. The cross slide is narrow and short, so this also severely limits the size of the work piece. The frame is lightweight, and while that might seem to be an advantage, it’s not. You want solidity if you expect smooth, accurate parts. A clarification: The X direction is left-right as you face the machine, Y is away from you or toward you, and Z is up and down. You’ll get a few basic projects done on this, but you’ll outgrow it quickly. It’s not capable of precision work, but then with a kit aircraft you’ll be building fi xtures and tools, not parts to put on the airplane. My friend Hank has one of these and when I asked if he’d buy it again he said, “No, if I had the money [there’s that perception again] I’d buy a larger one.” On the other hand, he’s working on his third airplane with it.

frequently when milling. This is a really great class of machines, and I would not hesitate to recommend them.

The Big Guns Door number four escalates to over $3000, with an increase in all areas. These machines are faster to change speeds and operations, and take larger parts, and now one brand includes a machine with a milling head that moves The bigger the spindle bore, the bigger the bar of material you can fit through the headstock.

The Mid Range Door number two goes up to about $1500. It has a larger, heavier bed and cross-slide, a few more speeds and maybe a second motor. Although it looks a lot like the $500 machine, this is where the issue of stability comes in: The milling head still rotates about the vertical axis, so you have wide-open access to the lathe section, but it can be solidly fi xed in place. Door three jumps us into the $2500 range. Now you’re getting two motors on some machines and a larger capacity. This machine is something you can use and grow into, but look carefully at the ease of raising the milling head. You’ll need to adjust that height fairly Two centers with a distance between them of 20 inches. This machine is capable of taking a much longer bar by removing the spindle (right). More on that later.

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Morse tapers. You can see that the one on the right fits into the drill chuck. No set screws or other captures are needed if you keep the surfaces clean.

R8 collets with an end mill. They get pulled tight into the quill via the drawbar. This clamps an end mill more firmly than a drill chuck.

only vertically. Anything in this group is capable of precision work that is, dare I say it, pretty. You can make parts that you may not want to use, just admire! This group can also be upgraded to

numerical control. That’s where you can motorize the motions of the cutting tool and the part. What good is that, you say? Those new, beer-can size motors are hooked up to that old PC you’re not

using anymore and, once the soft ware is dealt with, you can make parts that, not too many years ago, could only be made by Lockheed’s Skunk Works. A friend of mine installed it on his machine and for his first project cut his signature into a solid block of aluminum that now resides on his living room mantle. Go on the Internet and start looking at such sources as Harbor Freight, Shoptask, Enco and Smithy. These suppliers represent the range of features, price and quality. Tri Power machine. At $3000, we’ve reached the point of diminishing returns. Beyond this lies luxury.

KITPLANES May 2007

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Home Machinist, Part 2 continued

What Do the Specifications Mean? Here’s where things get confusing and the eyes glaze over. The specification sheet is a morass of unfamiliar terms and abbreviations. Smithy has a dandy CD that explains a lot of the terms and gives a nice introduction to machining techniques. But for now, let’s dissect the basic terms for the lathe section and their importance: Swing: 12 inches over bed, 7 inches over table. That’s the distance from the lathe rotational axis to the first thing a rotating object will hit. On a scale of 1 to 10, I’d give this a 5 in importance only because there’s not a lot of difference among the machines over $1000. Distance between centers: 20 inches. A long, small diameter cylinder has to be supported at both ends or it will bend away from the cutting tool. This is the maximum length of that cylinder if it were held in place between two “centers” and rotated with a lathe dog, which is a clamp that’s used to grip the part. It has a finger that intersects a rotating plate, causing the dog and part to rotate. This gets a 6 on our scale. Of course, if you anticipate doing long parts, this goes way up on your personal scale. Spindle bore: 1.03 inches. This is the maximum diameter of round stock that will fit through the rotating end

Smithy 1220 Ltd. Up another notch to $2500. We’re right at the top of the mostfor-the-money curve.

of the lathe. Say you want to make a 4inch-long widget out of 1-inch-diameter stock. You could cut a piece of material 6 inches long, clamp it in the threejaw chuck and make your part. But you would have wasted 2 inches of material. With this machine, you could put a 4foot long piece right through the spindle bore, cut the shape and then simply saw off the part. Voila! No waste and it’s quick to make a second part; just loosen the chuck, slide out some more material and start cutting. It’s sort of like the guy who didn’t want to chop firewood. He put the tip of the tree in the fireplace and, as it burned, simply pushed more tree in. I’d rate this as a 4 simply because in this class of machine, they’re all about the same size; you won’t find anything with a 2-inch bore. Tapers: headstock MT4,

tailstock MT3, R8. MT means Morse Taper. It’s a shape on the end of some of the tools that allows accurate and quick installation of items such as a drill chuck into the tailstock. There is no way to tighten it; it is simply slapped into the receiving hole and relies on the large surface areas and, occasionally, a tang to resist rotation. R8 is a taper that is used in much the same way. It won’t interchange with Morse Tapers and is usually used on the milling head. Its advantage is that it has a key slot to resist rotation and, in that its sides are slotted, a drawbar will pull it in tighter while exerting a clamping force on whatever tool is placed in it. You’ll need a set of about eight of these to get started. Both of these sizes and shapes are pretty standardized so don’t worry too much about it. Again, this gets a 4 and for the same reason as before.

Smithy model 1220. At about $1000 it looks, and is, worth the extra money.

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Speeds: 6 (160 to 1600 rpm). More is better, but easy shifting from one speed to the next is better still. This gets an 8 on my scale for the number of speeds and a 9 for the ease of the shifting. Pitches: SAE (inches) 6 to 30 tpi, metric 0.5 to 4mm. This describes thread cutting capability and gets a score of 3. Why? Because it’s a special skill that you likely will never get into. Travel: 20 inches longitudinal, 8 inches cross-slide. This is really important and a bit misleading. It says that the table will move in the X axis 20 inches, and 8 inches in the cross-slide in the Y axis. (X is left to right, Y is toward or away from you.) What it does not say is that you can’t cut something that size; tooling and clamping fi xtures will eat up a good percentage. How much is lost depends entirely on the setup, though, so it’s impossible to give an accurate number. While that X axis travel is adequate for most of the lathe operations, this spec is really important for the milling operations. It gets a 9 on my importance scale. The same thing is true for the Y axis; it is important only for large-diameter parts on the lathe, but you will definitely use it all for all of your milling. Because it’s the smaller of the two travels, every inch is critical, so it gets a 10 on the importance scale. Whatever you buy, you’ll need to put it on a very solid base; these three-inone machines weigh 300-1000 pounds, so don’t plan on putting it on that wood workbench you made out of an old kitchen counter. The suppliers have steel bases, so count on buying one. When it arrives you’ll find a big box of hardware that can be quite intimidating to the beginner. Trust me, there’s no way you’ll use it all at once, and some of it you may never use. Next month we’ll talk about what’s not used much, what’s essential, what’s hot and what’s not. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

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Comparing the options: the milling head.

BY BOB FRITZ

A

pair of 8-year-old girls approach the workshop, ice-cream cones in hand. First girl in a Lily Tomlin/ Edith Ann voice: “Whatcha buildin’, Mister?” Hank: “An airplane” Pause…lick…pause. First girl: “Does anyone know?” My friend, Hank, loves to tell that story. He says that she said it with great concern. He’s working on his third airplane, so I guess by now the word is out. Yep, number three. First, an RV-4, then a Lancair 235 with a Mazda rotary engine, now another RV-4 with a Lycoming O-290 built out of parts he had on the shelf. If you like to build,

well…build. But for this sort of involvement he definitely needs, and has, a home machining center. Last month in this series we described the lathe portion. Prior to that, we pointed out that it’s the perception, rather than the reality, that inhibits popping for $3000 for a machining tool, while 10 times that is OK for a boat. This month all that remains true, so let’s take a look at the mill head. The milling head is the part of the mill-drill-lathe (three-in-one) machine I find most useful. It’s the part that can cut a square hole or make a nice flat spot for attaching some other part. Think of it as a rotary knife; the milling head is your handle, and the end mill is the blade. It’ll cut aluminum more easily than a jackknife cuts soft wood, and you’ll find that it’s really fun to watch the chips come flying off, exposing bright metal. Now before you get your knickers in a twist thinking that the required skills Speaking of knives, an end mill is sharp enough to cut your fingers even when not spinning. Here’s an intake manifold being modified to take fuel injectors on my RV-6 project.

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are way beyond you, consider that both a surgeon and Tom Sawyer use knives, and so it is here. The surgeon has a high (you hope) skill level. But you’re like Tom…you’re whittling. By that, I mean that you should not be intimidated by the skill level of the professionals. Visualize a more realistic goal, say, Crocodile Dundee “Nah, that’s a knife!” What are we looking for in the mill head portion of our three-in-one machine? For starters, the same as on the lathe section. What’s stationary should be solid; what’s moveable should be easily moved; what’s adjustable should be easily adjusted. Specific to the mill head, however, we get a bunch of terms that might as well be Star Trek technogibberish. Let’s check a set of specs for a typical machine and see if Geordi LaForge can explain.

Mill Spindle Center to Column (Throw) 16 inches Translation: How far can you work from the edge of the material? Importance? That’s for you to decide, but 16 inches is average for this class of machine. What it amounts to is that you could drill a hole dead center in a 32x32-inch plate www.kitplanes.com

A good machine allows movement of the entire milling head, thereby minimizing the amount of quill extension. That, in turn, keeps the end mill more stable. It also allows for taller parts. Here, the head is all the way down.

Here’s one way of using the blocks to clamp a part above the bed. This allows you to cut through the part without cutting the bed itself. If you had an Erector Set as a kid, you’ll love these.

of metal. That’s larger than I’ve needed on my projects. For me, it’s an 8 on the importance scale.

Quill Stroke 3.25 inches Translation: This is how deep a hole can be drilled, and it rates an 8 on my importance scale. The quill itself requires a bit of explanation. It’s the cylinder of steel that supports the cutting tool. In the stability department, it’s the weak link in the entire system because it not only has to go smoothly up and down, it has to allow the cutting tool to rotate while resisting side loading in any direction. If you can get your hands on a machine prior to purchase, look closely at this component and make sure it moves smoothly up and down and in no other direction.

Quill to Table (Adjustable) 4-14 inches Translation: On this machine, the whole mill head goes up 10 inches for extra working space. This gets a solid 9 on the Bobometer because it’s so useful in minimizing the quill extension. It stands to reason that if the quill has to resist side loads, the shorter the extension the better; and being able to bring the head down to the work does just that. Photos: Bob Fritz and Courtesy the Manufacturers

Mill Table Size 9x19 inches This one’s not even Klingon, so it’s fairly obvious. However, don’t be fooled into thinking it’s too small. With a bit of ingenuity you can clamp some pretty irregular sizes and shapes onto the table. We’ll show you some clamping techniques in a later issue. Again, this is a high score of 8.

Mill Table Travel 10x23 inches You clamp your material to the mill table, and the amount of travel dictates the size of the working area. The smaller dimension is the Y direction travel; the larger dimension is the X direction travel. While a two-ton, $20,000 Bridgeport mill has something like 18x36 inches, I rarely used the extra area for anything other than a worktable when I had one. Bigger is better, but this is adequate for the home shop.

the best in surface finish, thread cutting or computer control. I give it a 6 only because you’re Crocodile Dundee here, remember? I’ve got powered L-R (Left-Right aka X axis) but use it only when making a cut longer than 2-3 inches. The F-R (Front-Rear aka Y axis) is neat but not vital.

Spindle Taper R-8 This describes the outer shape of the collet that holds the end mill. There are 30+ shapes, but R-8 and 5C are the two most common, and there’s not much to recommend one over the other. Just know that they are not interchangeable, with R-8 having a slight edge in commonality. When you want to drill a hole you’ll

Mill Table Powered L-R and F-R, Yes This refers to having motorized travel of the mill bed. It’s nice, but vital only for The T-nuts and slots along with the stepblocks allow you to clamp down odd shapes...like intake manifolds.

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Home Machinist, Part 3 continued find that the drill chuck is a bit different from what you’re accustomed to using on a dedicated drill press. In this case, the chuck is removable and will have the same tapered shape. The photo shows an R-8 collet with an end mill. It’s pretty obvious that you’ll need a set of collets to go with a set of end mills. Don’t panic, a nice set of collets can be had for less than $50; likewise a set of end mills.

A quill stroke of 3-6 inches is typical. Gross vertical movement is controlled with the 10-4 o’clock handle, fine movement by the crank, and depth control to 0.001-inch by the dial on the 10-4 handle.

Spindle Speeds (16) 125-2400 This comes under the Bill Gates scale of importance. If enough is OK, more is better, and too much is just right. This is too much, so it’s just right. Seriously, you’ll only use four or five speeds, but the problem arises when the group of four or five you want doesn’t include one that you have. I give this a 7 on the importance scale.

Motor Horsepower 1.5 You don’t want a wimpy half or three-quarter horsepower motor. This gets an 8.

T-Slot Size The T-slots are those grooves you see in the cross-slide table. They’re used to bolt things down solidly so you can cut them. Most tables have two of these grooves, while some have three, and one

Here the milling head is all the way up. You can see the crank sticking out the top over at the left end. Make sure this adjustment is easily accomplished on whatever machine you select.

The major parts of the typical combination machine will vary in color and shape among models, but the basic parts are the same.

brand has additional grooves that enter at 90° into the longest grooves. Three is better than two, and side grooves are

better still for making a setup easy, so this gets an 8. As for the T-nuts that go into the groove, you’ll buy a set of them specifically for your machine (they’re usually included on the better machines), so don’t worry about it. Score: 3 on the Bobometer. Although the T-nuts are not a point in evaluating the mill itself, a bit of explanation of their use goes a long way in understanding the entire machine. The table, as I said, has slots in it and the T-nuts fit in the slots. Here’s where An entire set of nuts and blocks is essential. If it’s not part of the machine, then buy it. Next month, we’ll talk about accessories and where to get them.

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KITPLANES June 2007

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This is a typical R-8 collet. Each is sized to match a different size end mill. As you can see, the top end is threaded to pull the collet tight, while the keyway stops rotation as you do so.

it gets to be fun. You select the clamping pieces needed for your particular setup, align the material so that the travel of the table matches the finished cut, select the cutting tool and voila. You’re ready to start cutting. Just remember to clamp the material at a minimum of two places and as close to the cut as possible. As you can see, the sawtooth blocks allow you to adjust the height easily. Of course, if you don’t need to cut entirely through the material, you can build a shorter setup that clamps directly to the table. And that segues into the entire clamping setup. This is like that Erector Set you had as a kid: lots of fiddly bits that help you build something substantial. This should help you understand the basic parts and specifications of the milling section. Next month we’ll expand on the accessories and discuss some of the things that come in the box with the mill. We’ll also examine a few of my favorite items and why they are indispensable in my shop. Now go lay out the area where you’re going to put this new machine! Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

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55

What’s in the box, and how to accessorize.

BY BOB FRITZ

“T

he most important thing to keep in mind is that there must be a logical solution to the problem. (This isn’t always true, but it’s good to keep a positive attitude.)”— Anonymous You opened the box and there it is, that new three-in-one machining center. You finally got your own milling machine, lathe and half-inch drill press. You know right where it’s going to go, so out comes the base. You level it, and then get an engine hoist and couple of

friends to help you get the machine in place. Looks great! But then your buddy says, “Hey, what’s all this stuff in the box?” You don’t want to sound like a complete dork, so you say, “That’s the stuff in the box.” Although it varies greatly with the price of the machine, in the box you might find a three-jaw and a four-jaw chuck, a toolpost, vises, cutting tools and clamping essentials. There are probably a lot of hand wheels, levers and other bits that need to be installed as well. Each machine is different, but if you’re sharp enough to build an airplane, those will be easy to figure out.

The Lathe Section: Chucks First let’s go to the lathe. Securely and accurately clamping the material you’re going to cut is essential. If the material is cylindrical, it’s fairly easy with a threejaw chuck because there’s a spiral gearing inside it that moves all the jaws at the same time. It’ll take care of 99% of the work you do on the lathe. But if you want to cut a 2-inch-diameter pocket into material that’s not cylindrical, you The three-jaw chuck will take care of 99% of your lathe needs.

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KITPLANES July 2007

For the other 1% of your lathe needs, you’ll want a four-jaw chuck. Note how the material is neither round nor on center, which allows us to put a hole of any size or shape in any location.

need the four-jaw chuck. On it, all the jaws move independently. With the aid of a dial indicator on a magnetic base, you can adjust the position of the material with great precision. However, it is usually easier to simply set up the mill to do that same operation, so it’s likely that the three-jaw chuck is all you’ll ever use.

Tools and Toolposts The toolpost is the next biggie. This is what holds the lathe cutting tool. If you took a high school metal-shop class you’ll think that this is a hot setup www.kitplanes.com

Center drills come in different diameters and lengths. They’re inexpensive, so buy a variety.

This ordinary drill chuck is held into this R-8 collet purely by the tight fit of a Morse taper.

Turning the small crank on this compound slide will cut a taper on the aluminum bar. Note that this toolpost allows a quick change of tools by simply rotating the red knob.

because it holds four tools at one time and can be rotated to get the next tool. And while it will work, it’s often more of a hindrance than a help because those other three tools usually get in the way. For about $160 you can, and should, buy a quick-change lathe toolpost set and relegate the other one to the “Interesting doorstop you’ve got there, Vern” category. It comes with not only a couple of holders for the cutting tools, but a boring tool holder (it’s actually quite Photos: Bob Fritz and Courtesy the Manufacturers

interesting once you get to know it), a knurler for making a good gripping surface on a shaft, and a parting tool holder for cutting off the finished part without taking it out of the lathe. We’ll discuss using all these in some detail in future articles, but for now just know that you’ll find the tools useful, and the ability to use just one tool while having quick-change is a real pleasure. Where do you put these cutting tools and the toolpost? Why, on the compound slide, of course. Wasn’t that obvious? No, of course not! Take a look at the photo of the toolpost. See that mechanism that sits at a funny angle? That’s the compound slide. The cross slide lets you move the cutting tool in the Y axis (that’s in-out), and the bed carries the cross slide, toolpost and cutting tool in the X axis (that’s left-right). If you want to make a cut at 23.5°, that’s where the compound slide comes in. Loosen the locking nuts, rotate it to the angle you want, check the clearances, use the levers on the cross slide and the bed to lock them in position, and then turn the compound slide’s own hand wheel to put that nice big bevel on the round stock. Easy. The lathe cutting tools usually come in two classes: carbide and high-speed steel (HSS). Carbide lasts longer and is thrown away when it chips or goes dull. HSS can be resharpened and formed to make a special shape, but it takes a bit of skill and a fine-grit wheel. This is the old technology and not what I’d recom-

They’re not sexy, but these parallel bars are as indispensable as a good vise.

One good use of parallels is to hold the material perpendicular to the drill axis but above the bottom of the vise. This allows you to drill through the material without drilling into the vise.

mend for a beginner. The pros use them only for special jobs. The carbide type tools are divided into two types: one-piece and changeable insert. One-piece tools are about $2-$3 each, which is tempting, as you’ll need at least two types, a left-cutting and a right-cutting, and several of each because they can’t be sharpened; you just throw them away. That’s about $25. The insert-type tool costs about $3 per insert plus the cost of the holder. You can get a decent set of holders for less than $50, and now it’s starting to look expensive. The inserts, however, have six cutting edges instead of one, so the entire setup could have been paid for with the second order of one-piece tools. An added bonus to the insert-type tool is that the cutting edges are usually formed so that the chips break into little bits instead of coming off as long wires. That makes for much easier cleanup. KITPLANES July 2007

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Home Machinist, Part 4 continued Right now somebody out there is saying, “What about TiN and cobalt?” TiN is short for titanium nitride. It’s a goldcolored, super-hard coating. Great stuff for keeping the edges sharp, but once it wears off you have a snazzy fishing weight. Cobalt tools are really hard and they don’t wear off like TiN, but they’re more expensive and they chip just rolling around in a drawer; if you drop it once, you can drop it a second time into the trash.

The Mill Section The milling head is a bit different in that the part doesn’t spin, the tool does. In the box you’ll probably find a drill chuck attached to an R-8 collet, maybe a couple of other empty R-8 collets and some end mills. Take one of the R-8 collets and look at it, and you’ll see in a moment how it works and that it fits only one size of end mill. Conclusion? If you need a different size end mill you need a collet to go with it. One quick aside: R-8 collets are threaded on the inside, and 5-C collets are threaded on the outside. The R-8 is more common, but be aware of what you have, because you will want to buy a set of collets and a set of end mills to go with them. You can purchase a nice set of end mills for about $60 and a set of matching collets with a holder for around $50.

The triangles are carbide cutting tools that can be rotated as the edge dulls.

That pretty much covers the useful, basic items in the box, but to really get rolling you’ll need a few other items. There was a humorist/singer back in the 1950s by the name of Oscar Brand, who wrote a song about a guy who bought a humble little MG sports car. Then the guy bought accessories, lots of accessories. By the time he was done he had spent enough on accessories that he could have had a new Aston Martin. Although you certainly don’t have to, you can do that with a three-inone machine, and it will be a lot of fun because you’ll find virtually all of the accessories useful.

The Vise and its Accessories First, there is the vise. It’s a simple clamp, but don’t be fooled into thinking that a

Skybolt sells this special tool for installing quarter-turn fasteners, but it’s more fun to make it. In the next installment, we’ll do just that—including the knurling.

vise is just a vise. This is what’s gong to hold your part 75% of the time, and if it doesn’t hold that part solidly without damaging it, well, it’s worse than useless. It’s not a simple matter of honking down on the handle and just getting

From left to right: the knurling tool holder, the boring bar holder, the toolpost, two cutting tool holders and the cutoff tool holder. These are some of the nicest ways to make your lathe a quick and fun addition to your shop.

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KITPLANES July 2007

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This is a usable toolpost, but not a great one.

tighter. Oh, no. The jaws of the vise should be, and remain, parallel. This is not simple because the tightening screw usually is not in line with the part being clamped; hence, it has a tendency to push the moving jaw out of parallel with the stationary jaw. The result? Parts that move. That movement is frequently further into the path of the end mill, which cuts a huge gouge into the material and maybe even breaks the end mill. Bang is not a good sound in the shop. Not everything in the box is useful. For instance, there might be a vise that can be tilted up on an angle. With it you can hold the part at an angle to the table, which would let you cut a bevel or even a V-shaped groove. This would be a great feature, if it worked, and if it held the part firmly in place. But take a closer look. First, check the moving jaw. Does it have a lot of play? Does it wiggle left to right and up and down? Not good. If all it has are a couple of thumb screws to hold its position against the power of the end mill it’s another interesting doorstop.

A vise like you’ve seen in a professional machine shop goes for about $600, so that should be a clue to its importance. You don’t have to spend that much, though, to get an acceptable one. I found one for $100 that works fine and rotates about the vertical axis. I’ll buy a good angle vise later when I need it. Two things that were probably not in the box, but should have been, are a set of parallels and a few center drills. The parallels position your material in the vise so that the bottom of the material is perpendicular to the end mill or drill. The center drills are perfect for starting a hole in curved material. Imagine using a 6-inch-long, number 40 drill on tubing; it would jump around more than a break dancer on his fifth cup of espresso. That covers what’s in the box and suggests some upgrades. About now you’re wondering where those bargains are. Well, go to www.use-enco.com and order the catalog. You’ll alternate between drooling and glazing over. Don’t be intimidated by the sheer volume of parts; the company has a great tech support crowd to help you find the right item. When you come up for air, finish organizing your stuff, and next month we’ll do a simple lathe project where we’ll actually build a useful item that could save you a few bucks. It’s a tool for inserting those snazzy quarter-turn cowl fasteners from Skybolt. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

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57

We complete a project on the lathe.

BY BOB FRITZ

“T

his piece of work fills a much needed gap.” Read that twice. Did it make sense? No? Good, you’ve just proven yourself capable of building this next part. As promised in the last installment, this month we’re going to make aluminum chips. Skybolt (www.skybolt.com) sells a really nice set of cowl fasteners

that I used on my RV-6, but they require a special tool for installation. Now I know you can buy this item, and maybe you don’t use their cowl fasteners, but it’s a nice starter project in that it requires several basic operations and results in a useful, finished product. Before we jump into this, there’s one more thing you should buy. It’s a little paperback book called Machinery’s

Handbook Pocket Companion. You can get it on the Internet for about $20. While it’s not exactly Agatha Christie, it will solve a lot of mysteries such as what feed and speed to use with which material, and when it doesn’t look right, what to do about it. Also, before we proceed, a disclaimer. This series of articles is targeted to the reader who is curious about the basics and doesn’t know what to ask much less what to buy. My use of a particular machine should not be construed as an endorsement or recommendation. Now on with the project.

Feed and Speed You’ve probably heard these terms, but throw in surface feet per minute and you have three more pieces of that jigsaw puzzle I alluded to earlier. It seems obvious that a lathe with 20 or more different speeds must have them for a good

The push tool. The item in bubble 1 should be kept square; don’t round it off. Bubble 2 is the knurled area. The marks on the material remind you of where to start/stop a cut, knurl or taper.

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KITPLANES August 2007

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The 6-inch ruler leans toward the operator, so raise the cutting tool a bit.

Face off the end with the right-cutting tool.

The expander tool. Make it from mild steel and note that the 0.470-inch dimension is the only critical area.

reason. Looking in Machinery’s Handbook will explain, if not why, at least what rpm is needed for a given material. We’re going to start this project using 1-inch diameter aluminum. It should be obvious that turning a 1-inch diameter at, say, 500 rpm means the material will go past the cutting tool a lot more slowly than a 2-inch diameter piece would. The number you need to determine first, therefore, is sfpm, or surface feet per minute for a given material. Review the handbook under “Cutting Speeds and Feeds—Turning— Light Metals” and on the appropriate page you’ll find “All Aluminum Alloys —Turning 600/500 sfpm.” To convert that number to rpm we could either calculate it or just go to Table 12a: “RPM for Various Cutting Speeds and Diam-

Start the taper and get a nicely curled chip.

Photos: Bob Fritz

Right- and left-cutting tools are in the same holder. We’re holding the protractor against the compound-slide so as to measure its angle relative to the cross-slide. The angle of the tool doesn’t matter...yet.

eters.” Looking across the top to 550 sfpm and then down the chart to 1 inch, we find 2100 rpm. Configure your lathe for that rpm and let’s set up the cutting tooling. Selecting a cutting tool may seem a

bit mysterious at first, but it’s not nearly as tough as figuring out if the killer was Colonel Mustard or Professor Plum. Sure, if you’re going for the ultimate in finish and speed, it becomes a science unto itself. But for our purposes, a

Finishing the taper will take several cuts. No rush, just educate your hands as to what a clean cut feels like.

Center drilling removes any vestige of a high spot. This makes the subsequent drill bit find exact center.

KITPLANES August 2007

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Home Machinist, Part 5 continued couple of general purpose cutting tools will suffice. All you have to do is look closely at the tool to see which way it slopes. If, with the shank of the tool towards you, the high edge is on the left, it’s for cutting when moving to the left. Just look at the tool and you’ll quickly figure it out. If it has no slope it’s for cutting left or right, but won’t give as pretty a finish as a specialized tool.

You’ll see chips like this to a depth of about three times the diameter of the drill bit.

Facing Off Our first operation will be to face off the end. Doing so will take the tool across the material from edge to center, which is also a left-to-right motion, so a rightcutting tool is required. Mount the tool snugly with at least two of the set screws in the tool holder. I like to use just two, because that way I can put another tool facing out the other end of the tool holder. That probably doesn’t make a whole lot of sense yet, but it will later. Just remember that when you tighten something, make sure it’s tight. Now we have to get the cutting edge

The boring tool sets up a bit differently than the other cutting tools. You have to first rotate the tool in the holder to get the cutting angle similar to that of the other tools before you set the height. Then check the clearance under the tool to make sure that the only part touching the material is the cutting edge.

Go more than five times the diameter of the drill bit and the chips usually start to pack in the flutes. Back out, clear them away and go back in. Repeating too much takes less time than digging out broken drill bits.

The knurl tool is simply two patterned wheels that push a pattern into the aluminum as if it were clay. Positioning the tool perpendicular to the aluminum will create a poor pattern.

Another quickie chamfer, this time internal. The author simply put a 1-inch deburring tool into a wood handle. A quick touch, and it’s done.

Although you could cut the chamfer, a file does a dandy job. Note that the author is in short sleeves and is working without going over the rotating chuck.

to be on the centerline of the material. With the tool in the holder and the set screws set, you can loosen the big nut on the top of the toolpost and spin the tool and holder around to get the cut56

KITPLANES August 2007

ting point to face the circumference of the material. Lightly tighten the big nut and then very lightly trap a 6-inch scale between the cutting edge of the tool and the stock. If the scale leans toward you,

the tool is too low. Back off and adjust the tool up a bit and try again. When the scale is vertical, you’re on target. What I like about the quick-change tooling is that once the height is set and locked, you can pull that tool off and put another one on with the flip of a simple hand lever (the big red knob in the photo). Get them all set and you can really keep on trucking. Now spin the toolpost around so that www.kitplanes.com

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the tool is in a position to cut across the face, and tighten the big nut. Your spouse probably thinks there’s a big nut loose on both ends of the wrench, but we’ll let that calumny pass for now. The moment has arrived; we’re going to make chips. Take a light cut of about 0.005 inch across the face of the material. For the first cuts you can either crank directly back or move to the right and then back. Reversing direction usually leaves a mark on the face, so going to the right to clear the material before backing off will prevent that and is good for making the final cut. Repeat this until all the saw marks are gone. We’re not a production shop, so take your time and learn the feel of the machine. This article is ground school and you’re going to solo, so just take it easy and don’t try aerobatics yet. Shut things off and take a close look at the end. If there’s a tiny bump remaining you’ll need to adjust your tool up or down half the diameter of that bump. Take another cut and now there’s no bump, so tighten the lock nut on the tool holder and call it good. Let’s take a very light cut on the outside diameter to begin with. You’re wearing the safety glasses, right? Set up a tool to make a left cut just as you did to make that face-off cut. I like to make the first cut by hand and very shallow, about 0.005 inch, to get the physical feel of the material and to ensure I’ve got the setup correct. Once it looks good, you can take a second cut about double the depth and maybe try out the longitudinal feed. Just remember to test the feed lever for direction and feel. You don’t want to be surprised to find it doesn’t disengage easily. As a precaution and as a practice, you might set the automatic shut-off. This is best done by cranking the cross-slide and the chuck well away from the material, then cranking the tool all the way to the left to where you want the cut to stop. Now, with the machine off, move the lever left/neutral/right and look for a corresponding motion of a long threaded bar just below the carriage hand wheels; that’s your auto-feed. On that bar there are two large threaded

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Home Machinist, Part 5 continued cylinders, one to the left of the carriage and one to the right. When the carriage touches those cylinders it will disengage the auto-feed. Set the one on the left to stop the carriage where you want, and move the one on the right out of the way for now. Then try it out while keeping a hand on the lever. Once it works like you expect, make another light cut. I like to mark my stopping points directly on the material with a felt-tip pen whenever possible. Just remember that for this part, the dimensions on the outside diameters are only approximates; we’re whittling for now. You don’t need to cut the area of the knurl at all. That process will cause the OD to increase, and the surface finish you start with will be destroyed in the process, so leave it alone. The next step is to drill the center out. Start with a center drill. You’ll find a lot of uses for a center drill because it’s so stout. That strength is specifically to allow you to put a starting hole exactly on center. Imagine trying to start the hole using a 12-inch #40 drill; it’d wobble around worse than my dog did when my brother and I fed him some of my father’s scotch. A short, stout drill is the just the ticket here. Follow that with a drill to go full length. This hole is rather deep; in fact, the ideal hole has a depth only two to three times its diameter. One reason for this ratio will become apparent as you get more than an inch or so into the aluminum. When you start the hole you’ll have two curled, wire-like chips

Cutting the taper this way makes it easier to cut the step.

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KITPLANES August 2007

This is the finished first half of the tool with part of the cowl fastener sitting on it.

coming off. But as you get deeper you might not see anything. It’s still cutting, but now the chips are packing the drill flutes. Back out and clean out the chips or you’ll break the drill. For a hole this deep, you may have to do this five or six times. Our last cut on the inside will be to bore out the 0.480 x 0.75-inch hole. Of course you could use a 31/64 -inch drill in this case, if you have one, but an inexpensive set of boring tools is a lot more fun and will always give you the size you want. The setup is the same as with the OD cutting tools. Just use a boring tool small enough to fit within the existing hole and put it on-center using the same 6-inch ruler technique as before. You’re beginning to see how these techniques build upon one another, so

The other half of the cowl-fastener tool is a simple part, but it’s useful for learning how to work in steel.

This is a parting tool. Its a bit tricky to select, set up and use. We’ll discuss it later. For now, simply saw off the almostfinished piece.

that what you learned in one technique is applicable to the next operation. That’s an indirect way of saying I’m not going to repeat myself for the next part. The inside diameter is important, so try to hit it within a couple of thousandths of an inch. The depth on the push tool is clearance, so go to the num-

Place the large half of the tool onto the taper, push the steel ring down the taper, and snap it on to the receiver.

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ber and a bit beyond. You’ll see how this all fits together at the end and it will make more sense than the opening paragraph, I hope. Now let’s cut that taper. The angle and outside diameter aren’t really important; close enough is good enough. Just set up a left cutting tool on-center as you did before. You can use that same tool holder that is holding the right-cutting tool, just put the LC tool in the unused half of the holder and then swivel things around until it sets up correctly. Now you have a fast way of switching tools. A pair of locking nuts are just above the cross slide, which will allow you to spin the compound slide around to achieve the 2° angle. As I said, the angle is not critical; it’s just visual clearance. All that remains is to check clearance and make sure you have enough travel on the compound slide to go the full length of the cut. If you do, have at it. This is getting easy, right?

On to the Knurl This is simpler than you might think. There are two tricks to the operation, though. The first is to get the tool to the right height. With the rpm turned down to as slow as possible, bring the two wheels up to the material so that they barely touch. One of them will turn, and the other will not. Raise or lower the tool as needed to get them both to turn at the same time without leaving a mark on the aluminum. The second trick is to rotate the tooling clockwise about 0.5°, i.e., just a smidge. If it’s square to the work you’ll get a lousy pattern. The nice thing about knurling is that if it’s not right on the first pass you can adjust the tool and take another; this is squashing the aluminum as if it were clay and in so doing, removes the previous pattern. Simply advance into the aluminum to give a light pattern and engage the feed to drive the tooling to the right. Back out, go to the beginning and repeat until you have a good, clean pattern. How deep is up to you. Go too deep, though, and you can create points that are hard to hold on to. I then like to take one last pass with the left-cutting tool to clean

up the interface between the OD and knurl, then a light pass over the knurl to make the pattern look really clean. Although we could use the parting tool, I don’t really like to as it’s tricky to set up; so for the moment, we’ll avoid it and simply saw off the part with about 1/ inch to spare. Clamp it back in the 8 three-jaw chuck, face it off, and add a chamfer to make it look good. Grin and give yourself an attaboy. The second part of this tool is much like the first. The big difference is that it’s made from steel, so you’ll need to go into the handbook for feed/speed and sfpm again. These numbers should be about one-quarter that of aluminum, and the part might benefit from the use of some cutting oil to keep the heat down. Just drip a bit onto the cutting zone as you go. Also note that this part is easier to make with its taper facing the other way. Try it both ways to see what I mean. It’ll be obvious once you attempt to cut the small diameter along with the maximum diameter of the taper. Oh, and that maximum diameter of 0.470-inch is really the only critical dimension. Make it too small, and the snap ring won’t expand enough to go over the mating part. Go more than, say, 0.480 and you’re doing more work than is needed when using the tool. Surface finish on the expander is also important. The snap ring will hang up on grooves or roughness. Wet or Dry sandpaper works well to get a good finish, and it’s better used wet than dry. I like to use chainsaw oil because it won’t fly off so easily. Even if you aren’t using these cowl fasteners, the operations we’ve shown are essential to almost anything you might want to make, so go make chips! Oh, and that starter paragraph about filling a much needed gap? It was in a movie review. Kind of twisted my eyes around until I figured out what it meant versus what it said. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

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KITPLANES August 2007

59

Tuning up the equipment.

BY BOB FRITZ

“G

ood tools aren’t cheap, and cheap tools aren’t good.”— Ron Neumueller. There’s an old adage that it’s the poor craftsman who blames the tools. While correct to a point, if you’ve started to cut metal, you’ve discovered the truth of KITPLANES® reader Neumueller’s mantra. The mill/lathe system is only as good as the weakest link, just as putting cheap tires on an Aston Martin is guaranteed to lose points on the “cool” meter—and may even put you off the road for your parsimony. I point this out because you’ve undoubtedly thought, “Phew, this is a bundle to spend, a lot of the tooling is included, and I want to get started.” As you got into it, though, you may have found yourself thinking, “Darn (or something more colorful), I wish I got better results.” While I agree that one problem may be that there’s a nut loose on the controls, there’s really no point in making the job harder by having to overcome tooling deficiencies. I say this not to repeat a previous column on the subject so much as to remind you that if

you’re frustrated by your results, make sure that the most easily fi xed cause has been identified and corrected.

Clear the Vicinity With that in mind, let’s look around the machine and see if we can tune it up a bit. First of all, before you do anything else, make sure you can get to all sides of the machine. When I first bought mine I was working in a one-car garage, so I put it tight up to the wall. It looked great, but after a few days I found that the starter-circuit points in both electric

A gooseneck lamp is essential to seeing what you’re doing. Don’t skimp here.

Use the screws on the ends at the bottom of the machine to get level in one axis.

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motors had welded and would not open as the motor spun up. It made a horrible noise and, if left that way, the motor(s) would have self destructed. I had to remove the motors and tear them down. You can guess which side of the machine I needed to get to. Once in position, take a look at the surroundings—I mean really look. Can you see what you’re doing? Is the lighting adequate or just barely so? You don’t need to rewire the shop; in fact, that might not help. The milling head is positioned above the work, so you need lighting that comes from the 10 and 2 o’clock positions. The easiest way to do that is to buy a clamp-on gooseneck lamp. Are you standing on concrete? While easy to sweep, it can lead to fatigue. Buy

a rubber mat or two, and place them in front of the machine and in front of the workbench. You’ll be surprised how much it improves your frame of mind. The type of mat with interlocks is good if you want a bigger area, but when you’ve decided how big you want it to be, cut off the interlocks around the perimeter; they trap chips, making cleanup a nuisance. Yes, I know, you want to get to the interesting stuff. Trust me, though. This process is like adjusting the seat properly before you fly; if you don’t, nothing seems to go right.

The Lathe, Levers and Levels With the working environment taken care of, let’s look at the lathe. Start by placing a level on the ways, first in the

XY direction, then across the ways. If it’s not spot-on, you need to get it there by using the adjusters down on the floor. Next, take a look at the various handwheels and levers. Are they tight on their shafts? Set-screws can come loose in shipping, or maybe they weren’t even installed when you opened the box. Get a wrench or screwdriver on every bolt, nut and screw you can to make sure they are secure. My machine was a mess when it arrived, and I had to spend a lot of time tuning it up. It’s annoying but necessary. Take a look at the oil level. Most machines have a sight glass somewhere. The upper level of lubricant should be visible. If it’s not, drain it and refill it with the recommended material. In fact, even if it’s full, drain it and refill to the mark—if it’s a new machine, you’ll want to know what kind of lube is in there. If it’s a used machine, you may not know the last time it was changed. Take a look at what comes out, too.

The Brakes

The spiral that drives the three jaws may have a lot of manufacturing trash. Cleaning it out makes spiral-made pieces nicer.

Clean the oil, and keep it at the optimum level.

I’ll bet it hadn’t occurred to you that these machines have brakes. They do, and they are easily adjusted. Let’s say you have the lathe head spinning at a couple of thousand rpm, and you hit the stop button. Imagine how long it would take to come to a halt if there were no brakes. Your machine is likely different from mine, but I would suppose they are similar in that something stationary is pushed against a spinning wheel. How hard it pushes is controlled by a setscrew. You’ll figure it out.

Lubricating the Gears My machine has an elaborate set of gears that are not submerged in the oil bath. As such, they make a racket. Go to the local motorcycle shop and buy a small can of chain lube. This stuff is great because it goes on as a low-viscosity foam that soaks into every crevice via capillary action. Turn on the machine to the lowest possible speed, and spray it into the point where the gear teeth engage. Then turn the level 90° and adjust for level in the other direction.

Photos: Bob Fritz

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Home Machinist, Part 6 continued Be careful not to get the nozzle stuck in the gears. It won’t hurt anything, at least it didn’t when I got too close, but if that had been my finger! In just a few minutes the lube becomes an extremely sticky grease that won’t fling off. LPS, ACF-50 and other spray lubes, while fine in many applications, just aren’t designed for centrifugal force. Chain lube is waterproof, too, and it works wonders on squeaky garage door mechanisms. Just don’t use it someplace where you’ll have to get it off later— and if you do, kerosene works wonders to remove it, or so says our motorcyclefanatic Editor in Chief. Carefully using chain lube is especially important if your machine is like mine and has belts in proximity to the gears. You don’t want to have lubricant on the belts. Speaking of which, take a look at the belts and pulleys. They should be aligned; if they are not, you’ll have to get them that way. I leave it to you to figure out how simply because this is not something that is typically adjustable. Over-tension, and sometimes lousy design, can trash a belt. If a belt doesn’t track correctly, fi x it or resign yourself to regularly replacing it.

Handy Gibs In the first column in this series I wrote about keeping things that should move, moving smoothly. So far we’ve looked at the generic issues. Now let’s go after those items that are unique to lathes. The gibs (pronounced as in glib, minus the l) are there to accommodate manufacturing variance and tolerance stack-up during manufacture. What’s tolerance stack-up? Imagine that you work on an assembly line, and you put the last part on the widget. You find that it won’t fit. You call QC, they come out with the print and measure your parts, finding that they are within tolerance. So they take the whatzit apart and start measuring all the other parts, only to find that they are all within tolerance. What’s going on here? The answer is simply that this device was assembled with parts all at the extreme end of their 56

KITPLANES September 2007

Use motorcycle chain lube only. Anything else will flip off, coating belts and making a mess. Just make sure to give the lube 10 to 15 minutes to congeal.

When the lever is moved, the ramp hits the set-screw and pushes the brake-plate against the rotating wheel. In this photo, the brakes are “off.”

And in this photo, the brakes are “on.” Properly adjusted, the system comes to a halt quickly and smoothly. It also cuts down on the motor’s start/stop cycles.

tolerance. The tolerances added up until your part, the last to be installed, would not fit on the gadget. You could take it apart, throw all the parts back in the bins, mix them around and not see the problem again. A lot of energy was expended on calculating stack-up and adjusting tolerances to looser or tighter values. About 30 years ago one of the European car manufacturers bragged that its inspectors outnumbered its assemblers. That not only didn’t say much to the good for the assemblers, it didn’t catch all the goofs and only increased manufacturing costs. The proper solution is to simply make every part exactly the same. I won’t go into this at length, but greater precision is the result of a series of process

changes, not simply tighter tolerances and throwing away parts that don’t meet them. That’s what we’re trying to do here. I must also point out that extreme use will cause wear, and the gibs will compensate for that wear to some degree. However, we’re not in that category of use.

Moving Along Now that you know what the gibs do and why they are there, let’s adjust them. The first step is to make sure the mating parts are clean with no burrs or rough spots. Start by loosening the lock nuts and backing out the screws. These screws are of the set-screw species, that is, they are pointed on the end and can only push. That means you don’t have to remove them, just get them retracted to www.kitplanes.com

The gibs are backed off enough to retract their points. Don’t forget to also retract the locking lever. The cross slide is moved to contact the point of the dial indicator. Note that the mount of the dial indicator is magnetic—handy.

There are three sets of gibs here, one for each locking lever.

allow the long bar to be pushed out. Tape a sheet of 320 wet-or-dry sandpaper onto a flat surface and add a few drops of oil. Any oil is fine, even 30 weight from the car or WD-40. Now just stroke the long bar around on the paper until you get a pattern for the whole length of the bar. Wipe it clean and slide it back into place. Turn the setscrews in until they stop, and then back off about 1/16 of a turn. Hold that position with an allen wrench or screwdriver and snug down the lock nut. If the component won’t move smoothly, you might have the set-screw too tight. Keep at it until it’s nice and clean in its motion. Don’t fool yourself by loosening them too much; you’re trying to adjust these to eliminate all movement except in the intended direction. Use a magnetic base and a dial indicator to check for movement in the wrong directions. Just touch the indicator probe to the component, set the dial to zero, and then grab and push-pull in the direction it should not move. You’ll find a place where the dial moves very little, perhaps only a couple of thousandths of an inch, but the entire assembly will move smoothly. This is a narrow window and might take quite a few tries, but it’s necessary if you’re going to eliminate the variables. If this doesn’t result in smooth motion of the compoAdjusting the gibs is fairly easy, and it has to be done to reduce the variables.

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Home Machinist, Part 6 continued

After a bit of smoothing on wet-or-dry, we have a nice, even finish. You only need to do this to the side that comes into contact with the ways.

nent, you may have a burr on the ways. Look for rough spots and loose debris; some of the machines I’ve seen were not cleaned well prior to assembly. Also try this in a couple of positions; it’s possible that the ways are not perfectly parallel. Once you’ve done that for the leftright motions, do it again on all of the other gibs. The procedure is the same; be patient and recognize that you’ll have a lot more fun later when what you wanted to do is what actually happens. A digression: Buy a surface plate. It’s a slab of granite that’s been ground to a very flat surface. They are amazingly inexpensive at about $15 for a 9x12 from Enco. If your lead screw is not protected by a cover, you should clean the threads frequently. But be careful that you don’t wrap the string around your fingers.

Routine Maintenance When all of this is done, you will likely find that everything seems to move pretty nicely. To keep it that way you have to keep the ways clean, and there is no more destructive environment for precision fits than one with scattered metal shavings all over the place. Therefore, wipe the ways down and clean up the loose debris at the end of each work session. Notice that I did not say to oil the ways; that will only attract more of the really fine bits. A spray of WD-40 followed by a thorough wiping will be sufficient. If you can get to the lead screw (it’s the long one that goes left-right, located just below the ways), take a piece of twine and wrap a half-turn on the lead screw. Turn the machine on to extremely low speed and then let the twine clean the threads. Be extremely careful here. Don’t take multiple wraps and don’t wrap the string around your finger. If the string catches, it could wind your hand into the screw.

The three-jaw chuck has a large spiral screw that can get filled with junk or just wasn’t really clean to begin with. It will come apart by simply rotating the T handle to loosen the jaws until they release from the main body. Use a felttip pen to mark which groove each jaw came from, as you’ll have to put them back in the same slots and then pick up the thread in the proper order. If you don’t, you’ll find that the jaws don’t all arrive at the center of rotation at the same time. It’s not a disaster, just an easily fi xed annoyance. Tuning up the rest of the machine is pretty much a variation on these procedures. For instance, the milling head has to have the tapers clean, the sliding surfaces smooth and free without unneeded slack, and the various belts aligned. It’s

Maintaining your machine will not only make your work safer and more enjoyable, but it will also improve the quality of the pieces you churn out.

not hard; in fact it’s mostly a case of looking closely, being careful, understanding what each part does and then putting it back like you had it, but better. Enjoy, and next month we’ll make a small project with the milling head. If you have some sort of process or project you’d like to see, let us know. No guarantees, but we’ll sure try to find the answer. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

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We complete a milling project. BY BOB FRITZ

L

ast month we did an introductory lathe project. This month we’ll show you around the milling machine in a similar fashion. OK, it’s not something everyone can use, but it’s something you can’t buy and if, like me, you use a PDA as a GPS display this will save your plug. Even if you don’t need it, the operations are a great way to get the feel of the mill. Besides, you may know someone who needs this.

Here’s the problem: My wife has an iPaq on the yoke of her airplane. It has a cord that plugs into the bottom edge. Said cord is easily knocked sideways and, at best, simply unplugged. If you’re lucky, you only have to plug it back in. If you’re unlucky, as was I, you’ll trash the plug. Do it repeatedly and I guarantee you’ll be unlucky. That means a new plug and the nuisance of micro-soldering. I don’t want to even think about the hassle, complexity and cost of fi xing the

socket end of the system should that bite the dust. The solution is to have a plug protector/strain relief so that the plug comes out only with a straight pull, not sideways. Or, more accurately, you remove the iPaq from the plug instead of the plug from the iPaq. That probably makes about as much sense as telling someone that the zero button on our airport gate keypad was installed upside down. I get a “His bungee was about 6 inches too long the last time he went jumping” look when I say this, until the next time they use it. (Look at your phone to see what I mean.) Conveniently, all you need, other than a milling machine, is a block of aluminum about 2.5 x 1.5 x 1.5 inches, an end mill in the range of 0.375 to 0.500, a 0.125 end mill and a fly-cutter if you want to get fancy. What’s a fly-cutter? It’s a cutting tool that spins a lathe bit. It’s great for making broad, but shallow cuts that stand above all other adjacent surfaces. This

The solution. We’ll glue this to bottom of the iPaq sleeve.

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KITPLANES October 2007

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Home Machinist, Part 7 continued will become obvious as we get into it. You can buy a nice set of three for about $25, so it’s one of those tools that’s affordable even if it only gets used a couple of times. Once you see how it works it’ll become a birthday-list item real quickly. My favorite source for this sort of tooling is Enco. While writing this, I checked the price: $21.40; on sale for $7.29 at www.useenco.com. Dimensions on this project are not critical, within 0.020 inch is more than sufficient. Now I’m not saying be sloppy, just don’t be more accurate than needed. Keep in mind that “quality” is not measured by the precision of the part, only by its success in meeting the customer’s requirement. Don’t believe that? Well, if I made, say, a shovel to within 0.0001 inch, is it a better shovel? It’s certainly a more expensive shovel. More significantly, it’s unlikely that anyone will pay me for that increased cost just because it’s a “highquality” shovel. On the other hand, you’re the customer, so if you will get satisfaction from making the part to tighter tolerances, go right ahead. Me? I’d rather get on with a second project. That said, we want the block to be held in some known position so that whatever level of tolerance we adopt, we

The material is 1.5 inches across. A flycutter makes a finish cut in a single pass and results in a nice finish. A 0.500 end mill would need four passes with a bit of overlap.

That scribe-line goes all the way across. Without the contrast it just disappears.

The finished part. Deburr it with a small file, wash off the Dykem with acetone, and give yourself a pat on the back.

do so intentionally. That concept means that the setting-up portion will take the majority of the effort. Think of it as a preflight drill; skip it and you may get to your destination, but you’ll have unnecessarily employed a lot of luck. Your mother taught you to clean up your bedroom and this is the same. Start with cleaning the mill. No, you don’t have to wax the paint; just get the chips out of the T-slots and wipe down the mating surfaces. If the T bolt is in place, try to get the chips out by dragging the

bolt. However you do it, the slot has to be clean at the start of every job. Clean the bottom of the vise and especially the jaws. Don’t get into the habit of using the air hose. You’ll blow those sharp chips all over. Safety glasses on? Better to use a brush dedicated to the task.

Be Square Next let’s square the fi xed face of the vise. This is an easily overlooked step, but I think you’ll see that it’s vital if you

You’ll note the absence of parallels under the part. That’s because clamping with less than the best vise will lift the material just enough that the parallels slide out. KITPLANES October 2007

53

Home Machinist, Part 7 continued want your part to come out square. My setup is fairly typical: I mounted a dial indicator on a piece of 3/8-inch round stock and clamped it into the mill head. One of the parallels clamped in the vise produces a surface that is, well, parallel to the jaws. Now move one end of the vise-parallel over to the dial indicator such that the point of the indicator touches the end of the parallel, and then go one more revolution of the pointer. You can zero it either by cranking on the X-axis handle, or just turn the dial of the indicator and zero it. You can see

what’s coming next, right? Move the vise on the Y axis and you’ll see by the motion of the dial indicator that the jaws of the chuck are not parallel to the axis of motion of the table. Loosen the bolts holding the vise to the table and gently tap the vise into position. Crank, zero, tap, crank, zero, tap until it’s acceptable. It’s not difficult to get it to within 0.001 inch over 4 inches of travel, so get it where you like it, tighten the vise to the table, and take one last check. Now we can break this setup and put either your fly-cutter or the 0.500inch end mill into the proper collet and mount it in the mill head. We’re going to take a cut on one side of the block and, inasmuch as four sides are already pretty close to square, we’ll trim off one of the saw-cut ends. The jaws of the vise define one axis of rotation of the block; you need to align the other. Here’s where you need an accurate square. That

24-inch carpenter’s square is not going to cut it, but the Mark I eyeball you were issued a few years back will work if you have a decent reference. I typically take the blade out of the adjustable square I’ve used for years and set it in the vise. Tighten the vise, and set your speed and feed. Now comes the math. Just diving in will frequently produce one of several scenarios: Too slow and the tool rubs, dulling it; too fast and surface finish stinks or things go ka-boom.

Don’t Panic! Remember that little book I mentioned previously? No, not The Hitchhiker’s Guide to the Galaxy. It was Machinery’s Handbook Pocket Companion. Going to Page 117, we see that aluminum is best cut at 500 to 600 surface feet per minute. Now I want to use that fly-cutter with a lathe bit that swings a 2-inch diameter circle. The formula is rpm = (cutting speed x 4)/fly-cutter diameter.

You’ll probably have to go to the local machine-tool supply shop to buy this. It’s great for tapping, too. Ask me how I know.

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First, cut the pocket. Then turn over the part and cut the base.

To adjust the block to perpendicular, it is held against the square and the square against the base of the jaws.

This was cut in several passes of about 0.050 inch per cut.

The calipers are sharp and hard and make a dandy tool for doing the layout. It takes a light pressure on the aluminum as you drag them to make a perfect line.

All three of these dials refer to depth, but how much is not obvious.

So, rpm = (500 x 4)/2 for 1000 rpm. That sounds about right, but what about the feed rate? Another formula applies: IPM = FPT x N x rpm. That’s inches per minute = (feed/ tooth) times the number of teeth times rpm. FPT controls the thickness of the chip and is, therefore, a function of the material we’re cutting. It comes out of Page 121 at 0.002 so: The feed rate is 0.002 x 1 x 1000 = 2 inches per minute. That will put one mark every 0.002 inches, but I want a nicer finish, so I’ll slow down to half that. Don’t extend this slow-it-down practice ad infinitum, though, or you’ll simply rub the material and create a dull tool. As you can see, the window of speeds and feeds that yield a good result is not tiny; with experience you’ll be able to set it up by eye. In fact, checking a halfdozen sources revealed suggested rotational speeds as high as 8000 rpm and as low as 3600 rpm for a 0.250 end mill. The variance is due to the sharpness of the tool, how long the tool must last, coolant used, etc. While we’re at it, let’s check those values for the 0.250 end mill. The result is 8000 rpm! My machine won’t even go that fast, so I’ll slow it down to about 1500 rpm. Yes, I know that I’m multiplying feet and inches. In this case using a correction factor of four removes the need to convert one to the other, and also eliminates having to use pi to calculate circumference. I’m just trying to make this painless. Doing it the long way results in 7640 rpm, which is still beyond my machine. Setting the feed rate with the same method, I get the FPT out of the book at 0.002. 0.002 x 2 x 1500 = 6 inches per minute.

That happens to be 1 inch per 10 seconds. My machine moves 0.100 inch per revolution of the handwheel, so I need to crank about one revolution per second. Those higher speeds work fine for huge NC machines that are flooded with coolant, so in addition to slowing down a bit, I’ll use a lubricant called Tap Magic. Neat stuff…you’ll smell like a machine shop and everyone will think you’re a real pro. Oh, and it helps make a good surface finish as well. One last thing to do before we start cutting is to check your dials. Make sure you know what each wheel does, that is, how far it goes in one revolution and what each mark represents. It should also be emphasized that, though you can turn the handles in both directions, if you overshoot the setting you want, back up one full, and then come back to the desired number. This is necessary to compensate for slack in the system. Now all you have to do is get the safety glasses on, review all the settings, make sure that the things that should be

The iPaq is held in place by a wraparound sleeve that is all but indestructible. The plug, however, has two microscopic hooks that can be destroyed with a dirty look. A dangling cable is its death. The aluminum cord-capture at the bottom is its salvation.

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Home Machinist, Part 7 continued

Keeping the T-slots cleaned out is made a little easier by simply sliding the T-bolts out. The slot can first be brushed, and then blown clear with low-pressure air.

Clean the vise jaws every time you remove the part. This is critical to having the part secure as well as square to the planes of motion. I like to brush out, and then wipe down the vise every time I open it.

Notice that the dial indicator is at zero. You can get there by either turning the black outer ring to move the markers or cranking the X axis. There are several types of dial indicators; I bought this one at a flea market for $5.

When buying a set of fly-cutters, don’t forget to get the lathe bits that go with it.

Generically known as layout fluid, Dykem is a favorite. The spray can is good for sheet metal, and the fluid washes off easily with acetone.

tight are tight, nothing is inhibiting the desired motions, and, with the power off, bring the cutting tool down to the highest point on the block. Move off to the side, power on, and go down about 0.010 inch to smoothly crank into that first cut. It looks good, so do this again to remove all the saw marks. The one thing we haven’t really discussed is the depth of the cut. An end mill can easily cut a slot an inch deep at the Skunk Works. For us, though, let’s keep it to about 0.050 until you get the feel. A fly-cutter, however, is a finishing tool; keep it to about 0.005 inch. Shut everything off, pull the block out, clean the vise, reset the block with the other end up, and trim that end to square. This is getting easier isn’t it? Like so many things, it’s all in the preparation; the doing is the easy part. Now is when I like to use a layout fluid such as Dykem so that I can literally draw the finished shape onto the block. I’ll do it several times during the build simply because I’m cutting material away and it helps me keep track of which side is which. From here on it’s a matter of cutting the pocket and slot. You should check the tool every so often for chip buildup. If it starts to clog the flutes, you’ll have to pick it out with an awl. If it clogs consistently, try putting a little Tap Magic on the tool and on the surface you’re machining. Wear a shop coat, though, and don’t drown the part; a little is suf-

ficient. Kerosene also works well, but its flammability and inconvenience make a dedicated cutting fluid a far better choice. The only remotely clever bit here is to cut the pocket first, leaving a thick base. That gives you something on which to clamp the vise. When the top is done, flip it over and you still have a lot of material for clamping. Now cut the base to the desired thickness. If you have not tried the fly-cutter yet, this is a perfect surface for it. The corners? I cheated by rounding them off on the Scotch-Brite wheel. Once the part is finished all that’s needed is to glue it to the back of the iPaq sleeve. Don’t have an iPaq? Design a different one to hold the cable on your setup, build it and send in a photo. I’d like to see it. I hope you realize that though this may seem a trivial component, general aviation has, until recently, been only slightly ahead of the Amish in adopting new technology. The force of homebuilders has been a key agent in blasting them off dead center. By taking up your own machining on your homebuilt airplane, you’re part of that pressure. Congratulations on joining the revolution. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

Once it’s on zero, move the vise in the Y axis. If the indicator moves, the jaws are not parallel to the axis of motion. 56

KITPLANES October 2007

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Part 8: A primer on threading. BY BOB FRITZ

W

e’ve looked at the machine and done a couple of projects; now let’s get into the nuts and bolts of it. Literally. For instance, how do you select the right drill if you want to tap a hole? Well, first let’s take a look at the nature of the threads. On first analysis, a thread is nothing more than an inclined plane wrapped around a cylinder. But it’s that wrap that makes it more than a simple wedge. Envision it as the circular ramp at a multi-level parking garage; it has a roof that limits the height of the vehicle. If that roof were variable in height and you had a tall vehicle, you might have a problem. But in our garage there’s a sign by the entrance that says the ramp is Class 3, so we feel pretty confident that it’s going to be consistent.

A Little Class That’s exactly what is done with threads, be they on the bolt or in the hole. Class 1 is a loose fit and will go together even if it is dirty. Now, that doesn’t mean this thread is poorly made; that’s an issue of quality control. Class 2 is common. It’s what you usually buy at the hardware store and is what you get with the

The rolled thread on the left has the grains of the material pushed into it. On the right, the grains are cut, resulting in open electron bonds, a fuzzy surface and microscopic stress risers.

majority of AN type hardware. I always thought it humorous that we pilots are fi xated on using Army Navy nuts and bolts. Class 3 designates precision fit. These are typically formed by rolling, not cutting. In addition to a precise fit, they’ve another advantage: They resist seizing. I’ll digress for a moment here to discuss seizing. The action of cutting any material is to simply pull apart the molecules and atoms that are either mechanically locked together or bound by shared electrons. Cut yourself a slice of cake and look at the rough surface. When you cut a metal you’re getting that same rough finish, but on a microscopic level. The surface is, in essence, fuzzy. When you tighten a bolt you’re forcing two surfaces together in a sliding motion that is flattening out the fuzz. You’re also pushing extremely small surfaces, the individ-

ual fuzz bits on the bolt, into close contact with the fuzz on the surface of the nut threads. When you reverse direction, that flat fuzz lifts up like the hair on a dog when it’s rubbed the wrong way. And, like the dog, it bites you. This lifting increases the force between the surfaces and literally welds the bolt and nut together. The result is a new string of words for the Oxford English Dictionary.

A board with accurately threaded holes is great for sorting out that coffee can full of bolts. But the screw pitch gauge is still needed for nuts.

Photos: Bob Fritz and Courtesy the Manufacturers

KITPLANES November 2007

55

The Home Machinist, Part 8 continued How to avoid it is fairly straightforward: Use a bolt with smooth threads. The ultimate way to achieve that is to eliminate the fuzz by rolling the thread. You’ve used a threading die and seen how it cuts the metal. A rolling die, on the other hand, does not remove the metal; it squeezes it in three rollers to push the metal into shape just as you would with clay. Not only does this minimize the fuzz, it increases the strength by plastically moving the grains of the metal instead of cutting them.

Designations The problem of seizing is exacerbated by the bolt/nut material. For instance, stainless-steel bolts on stainless-steel nuts are prone to this, so though they are great for corrosion resistance, they tend to become a permanent pair. A company I used to work for even resorted to silver plating all the stainless-steel bolts as a way of lubricating the threads. It didn’t do a lot of good, but it sounded like a zinger of an idea. One more designator: A is for external thread (a bolt). B is for internal thread (a nut or tapped hole). So a quarter-inch 28 2A designation tells us that we have a quarter-inch, 28 threads per inch, Class 2 bolt. Keep in mind that class refers to the geometry of the bolt. Grade describes the strength. Even more confusing is if we were to go into the hundred or so other thread forms including pipe, ACME, BAE, metric and Whitworth, so I won’t. Just be grateful that many of these thread forms are no longer used. If you’re like me, you have a bucket of mixed nuts and bolts with no idea of their size. While a screw-pitch gauge is handy, a plate with tapped holes in it is even handier. Remember that the screw will fit smoothly only if you have clean threads and the correct hole in the gauge.

Drilling That brings us back to the issue of drilling the hole. To get the maximum height 56

KITPLANES November 2007

The front side of the chart gives us the dimension of the fasteners, hole sizes for roll pins and even a bit of threading history.

Pipe thread size, bend radii, wire gauge, fraction to metric and clearances for wrenches are on the back side of the chart.

A close look at the bolt size section shows, in this case, all the dimensions of a 1/4-inch bolt, and drill sizes for UNF and UNC type threads.

of the thread, you’ll have to drill a hole that removes enough material for the tap to get in there, but leaves enough material for the finished thread. That, in turn, means that you’ll have to use drills that don’t always fall into neat increments of 1/ inch. Now, 1/ doesn’t sound like 64 64 much; it’s only 0.0156 inch or about the thickness of four sheets of paper. But

that’s about 70% of the thread height of a quarter-inch 28 thread. One way to achieve this is to have a full set of fractional drills (32 of them between 1/16 and 1/2), another set of numbered drills (0-80) and a third set of lettered drills (A-Z). That’s 138 drill bits! You won’t need all of those; after all, you’re unlikely to need to make www.kitplanes.com

Before you tap a hole, you have to drill it to the correct size. But a 3/8 -16 thread needs a 5/16 hole, a 6-32 thread wants a #36 hole, and a 5/16 -18 demands an F drill.

0-80 threads often. But even if you have all the drills, how do you select the correct one? Three ways: 1. Guess. This is not recommended, as you’re likely to either create a hole too large (which results in incomplete threads) or drill too small (which leads to breaking the tap); 2. Do a quick calculation as follows: Tap drill size = basic diameter of the screw - (1/number of threads) Say you want a quarter-inch 28 thread. Plug that in to get tap drill size = .250 - (1/28) That equals 0.250 - 0.0357 and comes to 0.214, which just happens to be only 0.001 larger than a #3 drill.

Eyeing the Chart While that sort of expertise is a neat way to show your mastery of the subject, there’s a better way to find the right size: 3. Use a tap-drill chart and read the drill size. The sine qua non of completeness is the plastic gauge from TAD. How much clearance is needed for a socket wrench? What’s the relationship between sheet metal gauge and decimal thickness? How big a hole do you need to get a roll pin to stay in place? And does a quarter-

inch 28 thread require a different drill than a quarter-inch 20 thread? Answer: Yes. The 28 thread requires a #7 drill, while the 20 uses a #3 drill. There are several versions of this on the market. Google it under “screw slide chart selector.” Still, that’s not exactly painless…you still need a lot of drills. Wouldn’t it be convenient to have a set of the most common taps with their matching drill bits all in one box? Well, such a set exists, and with Christmas coming up this is a gotta-have. Of course there are times when you need a hole to be just a little bit larger, but not too much larger. For that you will still want a good set of drills, and while the entire 170 pieces is a bit too much, a reasonable configuration is an all-in-one box holding 115 of them. This is much better than a drawer full of bits, because not only can you find what you want, you can easily spot the one that’s missing. Knowing that you’ll have to move the workbench to get it may be of small consolation.

The Perfect Combo Although a decent shop will have all 115 drill sizes, my favorite combination is to have the matched set of taps and drills paired with the Bullet-brand drills from Black & Decker. These bits are unusual

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57

The Home Machinist, Part 8 continued in that the ends of them are ground to smaller drill bits, so you get the no-wobble advantage of the combined drill/ countersink and can then continue the drilling. They also have the cutting edge ground so that the outermost diameter cuts first. Without that tiny drill on the end they would not have the self-centering effect of standard drills. But with the outer edge doing the cutting, you get a cleaner, minimum-burr exit when drilling through. I’ve also found that they resist grabbing when cutting fiberglass, so they’re my first choice in almost all situations. Burrs do happen though, and sometimes you need a countersink to accommodate a countersunk screw. Look closely at these countersinks, and you’ll see that not all cutting edges are alike. That small one with a hole drilled through it is dandy on aluminum, while the multi-flute versions work well in fiberglass. The straight, single-edge tools are good, general-purpose types. I have all three types because they are inexpensive, and if one is not working well for a given material and thickness, I try another. Be aware that they come in different angles of 60, 82 and 90°. Most screw heads are either 60 or 82°, so buy both and know which one you need when you grab it.

Black & Decker has come up with an unusual drill bit. The center makes it easy to start the hole, while the cutting is done at the outer edge so there is less of a burr.

Read Up With your appetite whetted you want more, right? Where can you find it? You may have shopped around and seen such tomes as Machinery’s Handbook and been put off by the price of $110, not to mention the 2618 pages. It’s overkill for the beginner, anyway. But there is a nice little book out there titled The Starrett Book for Student Machinists that can be had for $8 from www.useenco.com. It’s about 150 pages and only 4 x 6 inches in size, but has a lot of good information for beginners and not-so beginners. It has weights of materials, how to set up for knurling, sharpening a tool bit, figuring out what the material is by what sort of sparks it gives off when grinding, how to select hacksaw blades and a lot more. It’s in need of an update for those wanting to become professionals in that it barely acknowledges computer-controlled machines and makes no mention of computer-aided drafting, but for the beginner/home machinist type it’s quite good. Its other failing is that it has the tap/ drill chart buried in the middle of the book. That’s not too big of a problem, though. A visit to the local machine shop supply will usually get you a free poster or a pocket-size plastic one that includes metric sizes and a lot more. For the moment, here’s one showing the most common sizes.

Holding a wealth of information, this is a great beginning resource for the home machinist.

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KITPLANES November 2007

Four ways to countersink or deburr that hole. Each has its own best application; with several on hand, you’ll find the right way.

Threaded hole 4-40 6-32 8-32 10-24 10-32 1/ -20 4 1/ -28 4 5/ -18 16 5/ -24 16 3/ -16 8 3/ -24 8 7/ -14 16 7/ -20 16 1/ -13 2

Required drill

43 36 29 25 21 7 3 F I 5/ 16 Q U W 27/64

Trust me, this is not the entire story about threading. If it all seems a bit complex, consider that up until the 1970s bicycle manufacturers had their own thread forms. To buy a bolt for your bike you had to go to that dealer. No, I don’t mean 1870s. This particular insanity finally died a quiet death, but the trend toward standardization stalled when the issue became the demise of all but metric. So when you get that book, be glad that even though you’ll see references to dozens of thread forms, there are not nearly as many as there used to be. Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line.  www.kitplanes.com

Part 9: In our second lathe project, we fine-tune the lathe and use the calipers. BY BOB FRITZ

“H

ammer to shape, file to fit, paint to hide.” You could reasonably conclude that this is the factory motto if all you read was the instructions for fitting the nosewheel on my current project aircraft. The spacer is, I assume, intentionally too long, though why it should be is a mystery. However, the factory, quite correctly, points out that this will result in inappropriate side loading of the bearings and diminished life. The factory’s solution? “Grind it off.” And to emphasize what the company means, the manual shows the use of a heavy-duty, industrial grade, 90° grinder! It hearkens back to that hoary old definition of a professional mechanic versus amateur: The former has a greater selection of hammers. I suppose if you didn’t have any other method available this would have to do. Obviously, it works. But we, the home machinist types, do have an alternative: the lathe. First, let’s carefully examine what

Although this is exaggerated, it’s apparent that this is not the shortest distance between the two surfaces. The problem is that the base, resting on the upper block, is very small.

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KITPLANES December 2007

As supplied by the factory, the outer spacer, which bears on the inner bearing race, needs to be shortened to match the inner spacer, which extends completely through the wheel and bearing assembly.

After some quite easy lathe work, the spacer is the right length. It looks so much nicer than if it had been done by a grinder.

Here you see the rod end being used properly. However, this part allows us another option.

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we want to accomplish. The builder’s manual says that the spacers should not extend beyond the wheel hub. So I placed the hub on a small, flat steel block and gently tapped everything down. I say gently, because we’re dealing with bearings; they can carry quite high rolling loads, but a hammer is a load spike that can brinell a bearing faster than a seal going after a slice of fish. If you don’t believe it, push a hammer onto your thumb; now take a very light swing at your thumb. Like Oscar Wilde said, “The things that are really worth learning can’t be taught.” I hear someone out there saying, “Baloney! [Or something more flavorful, I suspect.] If that were true I’d never be able to drive my car through a pothole.” My response to that is to invite you to remove the rubber tires from the steel rims and change out the springs and shock absorbers for a set of lowrider hydraulics. With all that shock absorbency removed, go see how long the bearings last. Conversely, if you want to offer up an equivalent cushion, put your thumb on the bearing and then start hammering away; the bearing will survive quite nicely. Back to the spacer: How much do we need to take off? You sure can’t measure over the wheel to the other side very easily, but with an inexpensive, generalpurpose digital caliper you can directly measure the material to be removed. The trick to using one is to keep it perpendicular to the surface.

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Using the Caliper There are two ways to measure the offset using a caliper. The first, and most common technique is to use the extending rod at the end of tool. As you open the gap between the jaws, the rod extends in perfect synchronicity. While a dedicated depth micrometer is the ideal tool for measuring the depth of a hole, a good caliper will do an acceptable job of it. The advantage of the dedicated depth micrometer is that its broad base gives you a better shot at achieving perpendicularity. The problem, for those of us on a budget, is that they have a 1 inch range. You therefore need a kit comprisPhotos: Bob Fritz

KITPLANES December 2007

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Home Machinist, Part 9 continued ing a base and six rods to do what the caliper can do; the micrometer will only measure depth. If clearances allow it, a second method that comes closer to that perpendicularity goal is possible. Where in the previous method you could swing the tip of the rod in a circular orbit without knowing it, the caliper has a function that employs a larger base, minimizing that orbital movement. Why? Quicker, better results. We see that we need to take 0.032 inch off of the material. While we’re at it, get into the habit of putting a zero out there as the leading figure. It makes for less confusion when you have a dimension with a leading zero. OK, back to the project. We need to take off 0.032 inch from the end, so we set the part in the three-jaw chuck of the lathe and, because we’re going to cut across the face from the outside to the center, we select a right-cutting tool. We are going to cut across the end of the material, so we need to set up the tool so that it cuts through the centerline of the material. How to do this was described in an earlier article, but it’s such an easy and yet essential part of using the lathe that we’ll go through it again. Position the tool so that the cutting point is not quite touching the material

diameter and lightly lock it down. Now put a 6-inch steel ruler between the tool and the part, and crank in the tool just enough to hold the ruler against the part. Don’t overdo this; you don’t need any more force than the minimum needed to capture the ruler. Is the ruler vertical? No? If the top of the ruler is leaning towards you, the cutting tool is below the center of the part; leaning away, it’s above center. All you need do is back away from the material, adjust the cutting tool up or down to get the ruler vertical, and try again. The vertical positioning can be done by using shims under the tool, or better still, Here’s a better way to measure the height. When fully assuming your equipment closed, the OD jaws, ID points and rod are all flush to has this feature, by turning their adjacent surfaces. But so are the extreme left (when holding it horizontal) ends of the tool. That a knob that positions the means when you move the jaws, you displace the two tool holder in the Z axis. If largest surfaces. it’s not on center you won’t get a good surface finish and, when you Now we have to position the tool to cut across the end of the material, you’ll cut the face, so pivot the tool assembly leave a nubbin of material that looks around so that the tool point is about to ugly. There are times when you want to touch the end of the part and the cuthave the tool about 0.005 inch below ting edge is facing to the right. Finally, center, but that’s a little too advanced remember to tighten the tool down. If for us right now. it’s not secure, you could get a nasty surprise. Also get into the habit of removing the chuck key from the three-jaw chuck. Either your hand is on the chuck key or it’s out of the chuck. Neglect this and, if you’re lucky, the key will be thrown across the shop when you hit the start button; unlucky and it’ll whack into the lathe bed ways making all manner of expensive noise; really unlucky and you’ll get an even more expensive visit to the dentist when you wind up eating it for lunch. This is aluminum, and a pretty small part, but we’ll still check for feed and Here you can see that the high edge, the cutting edge, is set up to move from left to right; hence, it’s a right-cutting tool.

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KITPLANES December 2007

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This is what the ruler should look like when the tool is at the right height. The only way of creating this situation is to have the tool point at the same height as the central axis of the material.

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This view is from the end with you, the operator, standing to the left. If the ruler tilts away from you, the cutting tool is too high. If we were to take a cut across the end of the material, it would leave a bump of uncut material.

speed. Use any of the reference books you like, but at the moment I am looking at Machinery’s Handbook – Pocket Companion. It tells me that a turning operation for aluminum should be done at 500 surface feet per minute. Another chart within the book converts that to 1910 rpm for a 1-inch diameter bar. Having set that speed, we need to take a measurement from some fi xed reference point. Conveniently, we can

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KITPLANES December 2007

use that step function on the caliper and measure the change of extension as we cut. Simply set the calipers’ steps with one on the end of the material and the other on the jaws of the chuck; push the button on the caliper to set it to zero. Now, let’s get a bit clever. Move the jaws of the caliper together until they read 0.039 inch, and push the zero button one more time. Now all you have to do is cut off material and measure. When the caliper reads zero, you’re there. Let’s start with a minimum cut— just a few thousandths will do to make sure that everything is tightened down. Next, stop everything without turning either the X or Y axis handwheels, and then set the handwheel dials to zero. You can now move right (+X) and back out (-Y), restart the jaws turning, and then run the handwheels back to zero. You’re back where you started, and you know it because the dials say so. Just remember to always go past zero at least half a revolution before you come back to your mark. This is necessary to take the slack out of the gearing on the

handwheels. Neglecting to do so is the most common source of errors when doing any machining, so burn this procedure into your mind. Here comes the fun part. Move to the left (-X) until the dial reads 0.010 inch and take a cut; stop and measure it with the caliper. You’ll remember that we set up the caliper so that it would read zero when we got to the right length. We started with 0.039, and assuming we took 0.004 inch off on the first cut and 0.010 inch off on the second, our caliper should now read 0.025 inch. In fact, you could work it backwards as well. It started off at 0.039 inch too long, and we know that the second cut took off 0.010 inch; in fact, the Y axis dial reads 0.010 inch. The caliper tells us we have to cut off another 0.025 inch, so that first cut had to be 0.004 inch. That’s the fun of this little trick: you only have to do the math once, and then you just count down to zero. I’m cautious, though, so I would take another 0.015 inch and then 0.010 inch so as to get a better finish. www.kitplanes.com

Familiar with the Machine Although we’re not using the function here, I want to point out something that can really bite you if you’re not aware of it. The dials that indicate X and Z axis travel, that is to say left-right and updown, are direct-reading. If you move the dial 0.030 inch, the tool will move 0.030 inch. However, the Y axis, in-out, is not the same on all machines. On my machine, if I move it 0.030 inch, the tool moves 0.030 inch. Seems reasonable. If I’m taking a cut on the diameter of the material I’ll have a part that is 0.060 inch smaller on the outside diameter. That’s because I’m cutting the radius, but measuring the diameter. Being aware of it means that if I want to reduce the OD 0.030 inch, I have to move the dial 0.015 inch. For that reason, some machines are set up to move the tool half of what the dial indicates. Whenever you work with a new machine, test this to find out which system is built in. Finish off with a touch of a file to the outer edge, and then put a small chamfer on the inner edge. Why? Sharp corners are easily mashed over to create burrs and undersize holes. The inside chamfer is easy to do if you fit a large conical deburring tool into a file handle, and then just lightly touch the inside. Well, that’s it. Our first lathe project was substantially more complicated, but this one helped develop some sophisticated skills. In future articles we’ll detail the use of the boring head and describe work being done between centers. We’ll show the use of a moving rest that will allow you to reduce the diameter of long, skinny parts that, without a moving rest, would simply flex away from the tool. We’ll also show how to chuck up a non-symmetric part and then bore a hole in it off center. For now, sweep up the chips and wipe down the entire machine. It’ll pay back by making the parts easy to build, and the machine will last a long time.

INC.

Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line.  KITPLANES December 2007

33

Part 10: Deciphering technical drawings.

W

hich way is up? Is that the front or the back? Stupid drawings! If you’ve been bewildered by some of the drawings you got with your kit, you’re not alone. Some of the designers appear to have been intimidated by the more esoteric presentations and, for that matter, even made some very basic goofs. We won’t go into a full-blown explanation of the entire subject of drafting standards here—that requires several semesters of college-level courses and it is, even now, undergoing major changes on how dimensioning is done. What

In third angle projection you should imagine yourself standing inside not only the glass box, but inside the object as well. You could face the 12 o’clock position and you’d see the wall of the object. That view is the one projected onto the 12 o’clock wall and when that wall is laid out flat by hinging it up you would have the view you see.

Photos: Bob Fritz and Courtesy the Manufacturers

BY BOB FRITZ

we will do, however, is offer a couple of basics that should give you a shot at understanding even those drawings that bear an embarrassing resemblance to the runes carved on a Viking headstone. Isometric versus orthographic? You’ve heard the terms but probably can’t remember which is which. There’s an easy way: “Iso” and “graphic” translate to single view. And that, in turn, can be interpreted to mean one view shows almost everything. Having knocked off that definition, we’re left with orthographic. That breaks down to “ortho” and “graphic,” which translates to upright view. Simple, no?

In the upper left corner we see a single isometric representation; a single view shows all. The group of six views is all orthographic; each view is upright.

Well, no. There are types of each projection within those categories, so that’s a gross simplification. But for the moment we’ll leave it at that because these styles of ortho and isographic cover almost everything you’ll see.

The View The question then arises: If, in an orthographic drawing you can have several views, how do you know what their relationship is to one another? Are you looking at the right or left side of the thing? Can’t you just slap them anywhere on the paper? The answer is no. There are two principal methods for

This graphic is rotated 45° counter-clockwise so you can see the bowl and all the positions. That means that the 12 o’clock position is in the upper-left corner. To get a handle on the pictorials and positioning of a group of third projection orthographic views imagine the part sitting in the bottom of bowl. Sliding the part up the wall of the bowl lets us see the other sides. And if we slide it up the left side, we need to place that view to the left of the plan view. KITPLANES January 2008

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The Home Machinist, Part 10 continued

The lower view is the face of an RV-6 panel I designed a few years ago. The view just above it is the top view. Visualize the bowl, and you’ll see that this orientation is a third angle orthographic. But you’ll note that the altimeter, airspeed and artificial horizon hide everything on the switch panel below them.

In this sectional view we’ve sliced off the upper half of the panel and can now see the switchboard at the bottom of the panel. The slice-line is identified on the first view by a dashed line, two arrows and “D” at each end. That’s telling you three things: The horizontal line says where we cut the part; the arrows indicate the direction we’re looking; the “D” identifies this particular section. There could be several sections, so each is identified as “A” or “B” or whatever letter you like, and the section identifier is listed underneath.

placing the figures, and they result in confusingly similar but different layouts. They’re called first angle projections and third angle projections. The basic idea behind both is to float the object in a six-sided box, project the six faces of the object onto the walls of the box, and

then open the box to flatten it. The difference comes in the projection: First angle projection assumes that the side you see is projected onto the wall behind it. Third angle projection has a light bulb inside the object casting shadows of the object onto the wall nearest that side. Third angle projection is the standard for North America, so until the recent influx of kits from Europe, where first angle projection is the norm, things were not too confusing. The version used, first or third angle, is denoted by a symbol you’ll sometimes see on the drawing that probably left you wondering, “Huh?” Now before you go completely blurry over this, there’s another, and probably easier way to visualize the North American format, i.e., third angle projection. I call it the bowl method.

The Bowl Method Put the part in a bowl and look straight down at it. That’s the plan view. Now, keeping the part in contact with the bowl, slide it up the right side. That’s the right side view. Slide left, left view; slide to the upper side, top view. If the bowl were a clear glass sphere, you could keep

We can go further with this technology and quite easily get an enlargement of a specific area. That could result in too large a drawing, so we can select an area and generate a Detail View. In this case you see that the uppermost view, the sectional, has a dashed circle with an E. The degree of magnification is a simple push of a button, and now we can see the detail of the placement of the switches. Unlike the other view, section view placement is entirely arbitrary, though having it close to the source makes it easier to find.

coming around to the top of the sphere and you’d be looking at the bottom of the part. Much easier. The only wrinkle here is that if you’ve gone all the way over 180°, you should place that view on the paper just beyond the view it passed through. So let’s try that again. You want to see the bottom?

Sectional and/or detail cut-lines don’t have to be quite as tidy in their positioning as the instrument panel example; they can pass right through a “solid” part. This is handy to show a feature such as that curved interior that might otherwise never be suspected.

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On the left is a first angle projection; on the right is a third angle projection. Don’t try to understand the concepts by those names; there’s a logic to it, but it’s not important here. Just remember that Europeans use the bowl upside down and take it from there.

Slide to the right, get a right view and place it to the right of the first view. Now keep sliding in the same direction until it’s upside down. That’s the bottom view. You’ve been sliding to the right and putting the view to the right, so place this view even further to the right. What makes this last view a bit tricky is that for a part that is not symmetrical, you’ll get a different view if you go in a different direction. That’s why it’s important that you put the view in the correct position. Look at the drawing of the bowl and form a picture in

Viewed straight down that view of the part that’s centered on the bowls is identical. And when the part slides down the right side of the gray bowl (first angle) we see the figure 8. But when we slide the part up the inside of the blue bowl (third angle) we see the other side of the part, the side with the squared-off C. Take away both bowls and you have the same “front” view but a different “right” view.

A simple way of determining if it’s a third or first angle projection is to again use the bowl; if the bowl doesn’t work, then it’s probably first angle or mis-drawn.

Mis-drawn. I can only imagine your screams of confusion. But, and this is most likely, especially if the drawing came from Europe, it’s a first angle projection. How can you tell? Easy. Let’s try the third angle bowl one more time. In a third angle projection the bowl was sitting on the counter in its ordinary open-side-up fashion, and the part was resting nicely down in the bottom of the bowl. Look straight down on it; that’s the front view, and we drew it on paper. Then we slid the part up the right side of the bowl and that gave us the right view, which we drew to the right of the front view. Simple. To get a first angle projection we start by turning the bowl upside down, and the part just fell on the floor. Now place the part on the bowl in the same orientation as before. You look straight down at the part, you get the same picture as

The symbols to tell you which of the drawing conventions is used.

your mind of that representation at 12 o’clock continuing on around to the top of the bowl; the thin section is in the 6 o’clock position. Now take the view shown at the 3 o’clock position and slide it up to the top of the bowl; the thin section now points back at 12 o’clock, just the opposite of the first attempt. Go try it to see the effect. Get a salad bowl and a small asymmetric component and slide it up the wall; you’ll see how the views naturally fall into place and how it’s important to place that top-of-the-bowl view in the correct position.

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The Home Machinist, Part 10 continued before and you draw it on the paper. But now when you slide the part to the right, it goes down the outside of the bowl and shows you a different side of the part. The same practices apply for placing each of the views on the paper, and you’ll get that same reversal of some elements when tracking the final view from two directions 90° apart.

The Reasoning Behind It These conventions have been defined for only a century or so. Prior to that it was a free-for-all, or something that required a very good artist to draw accurately. In the past few years, though, engineers have been able to draw the object on a computer and then literally turn the item around as if it were a real object. That led to the possibility of being able to position several of the parts into a realistic-looking assembly. The advantage of this is the ability to check clear-

An iso/ortho drawing is useful for giving the viewer a fast idea of what we’re talking about and the details of size. But note that the “bowl” analogy applies to the orthographic drawings, making this a third angle projection.

A top-level CAD program will allow you to create the individual parts, assemble them and then, as in this drawing, even show it with a perspective view. Note that it’s smaller at the higher, right end, giving the impression of depth even though it is in actuality just pixels on a flat screen.

ances accurately and, consequently, increase the density of the part placement without worrying about needing a fudge factor. An even more immediate benefit is that libraries of everything from bolts to bearings are available with CAD programs, and the manufacturers are supplying CAD drawings of their products in an effort to get them easily specified into the next assembly. This means the designer can insert one ¼-20 bolt or a commercially available hinge, and then 56

KITPLANES January 2008

Creating all the parts, even the switches and the diodes on that green circuit board, allows the designer to feel confident that it really is a what-you-see-iswhat-you-get design.

use it throughout the drawing with the assurance that there is room for a wrench and the hinge really works. Because the parts can be moved, rather than just popped into position, the bolt can be extracted to check for clearance. You might remember pre-CAD automobiles that required the removal of a fender to get one of the spark plugs out. While there is no guarantee of that not happening now, the potential is enormously reduced. One of the most useful features is the ability to slice open the assembly and see how several parts interface. Back in the bad old days of 2H pencils and vellum this used to be an expensive and timewww.kitplanes.com

THE WORLD’S BEST TUBE BEADER! consuming procedure of hand drawing. With CAD it’s a matter of pushing a few buttons and a couple of mouse clicks. By the way, CAD is an acronym for computer-assisted drafting; ACAD and AutoCAD are CAD products made by one of the industry leaders. Now that the iso/ortho drawings have given us the big picture, we’ll use another type of drawing to get some details. It’s the sectional view, and it’s a favorite of designers. It has two uses: You can, in essence, get around the parts that are blocking your view, or you can slice right through a component to see a cross section.

Drawing the Line Finally, let’s look at the issue of line styles. If every line were the same we’d have a very confusing situation, so there’s a universal consensus on at least a few of the basic ones. They are: • Solid lines indicate a visible feature. • Dashed lines indicate a hidden feature. • Dash-dot is used for the centerlines of holes or other features. After that it goes into line weight, meaning line width, and a plethora of cross-hatchings to indicate everything from aluminum to zinc. Fortunately, that esoterica is not prevalent outside the confines of mega-tech companies like Boeing or Bell Helicopter. As was noted at the outset, mastery of this is not intuitive. It is a specialty so much so that when I was a design engineer, we would whip out a component and then send it to a group of specialists to clean up our digital gibberish and make it conform to the company standards. But the one rule upon which I’ve always relied is that clarity is more important than any rule. If showing it in a non-standard way is the only way to get the idea across, do it. Just be sure you’ve exhausted the standard ways first.

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Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line.  KITPLANES January 2008

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Part 11: The boring head and the traveling rest. BY BOB FRITZ

T

he boring head. No, that’s not a poorly decorated toilet on a yacht; it’s a neat little tool for making big holes, internal grooves and odd sizes of holes with the milling machine when a drill bit is not available. What? You don’t have a 1 1/32-inch drill bit? If you’ve been a regular reader of this series, you’re thinking that there’s something familiar about this tool, and you’re right. It was mentioned way back in Part 4 (July 2007, KITPLANES®, Page 54). At that time I mentioned that it was a favorite tool of mine, but I didn’t demonstrate or expand on that statement. Now let’s take a closer look. The boring head is simple enough. It holds a sharp cutting tool in a way that allows you to install it in a milling head and then spin the cutting edge in circles. This is not the same thing as what’s commonly known as a circle-cutter. The circle-cutter has a drill bit in the center with a lathe bit mounted parallel to the drill bit, offset whatever distance you choose. The technical name for this is trepanning, because it removes the core material in one piece. It’s a great tool for knocking out 3-inch-diameter holes in a thin instrument panel, but it won’t do a counterbore, and it’s limited to about a 1-inch minimum hole. Although the lower limit for a boring head is the size of the cutting tool, the realistic minimum is on the order of one-half inch. Take a close look at the head and its Photos: Bob Fritz and Courtesy the Manufacturers

From the left we have a counterbore, a countersink, a trepan and a spot face. You can see that the core of the trepan would simply fall out now that it’s been cut through. You’d use a boring head, a counterbore tool, a trepanning tool and an endmill to cut these.

That tapered shank at the right fits in the mill. The head holds the tool; the fat screw at the 5:30 position fine-tunes the diameter of the cut.

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Home Machinist, Part 11 continued operation is pretty obvious. What’s not so obvious is that you have to work your way out to your size, first drilling a starter hole and then cutting larger and larger circles. Even less obvious is that this benign little tool has to be kept on a short leash. As your circle gets larger, you have to slow it down—a lot. You’ll remember from earlier articles that the measure of cutting speed is surface feet per minute not rpm; SFPM is the speed of the tool over the material. To keep the SFPM to a reasonable level, you have to slow down as the hole gets larger. If the diameter of a circle doubles, the distance around the circle doubles. (Don’t confuse that with the area of circle, which is 3.14 times the radius squared. That goes up a lot faster with an increase in diameter.) As an example, let’s say you drilled a starting hole at 0.375 inch and want to enlarge it to 1.5 inch. That’s four times the diameter, so it’s four times the circumference. A check in the books (it’s quicker than doing the math) says that

Want a really big hole? Put the cutting tool in this way, clamp down the set screw, finetune the diameter, crank the rpm way down, and have at it.

Here’s the tool retracted for a nice small hole. That hole on-center can be used for even smaller diameter cuts. Your only limit is the size of the boring bar.

You can test a setting by cutting on a bit of PVC.

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5000 rpm is appropriate for 500 SFPM (appropriate for aluminum) on a 0.375inch hole. OK, time to apply some good sense. That might work for drilling a 0.375inch hole under ideal conditions, but not for us. For this tool in aluminum, 250 rpm is a good starting point because of all the extension and the unbalanced mass. You’d have to cut it back to about a quarter of that, i.e., 75 rpm, by the time you got to your final 1.5-inch size to maintain your SFPM. However, we cut it way down to begin with because of the mass and balance factors, so you can probably leave the speed a bit higher.

Additionally, you must recognize that the cutting edge is out on a long, slim support; it’ll chatter or even break the tool if you go too fast. Just to confuse the issue, I should point out that one of the recommended cures for a poor surface finish is to speed up the rpm. Obviously, this is a skilled and experience-intensive hobby. Getting the size you want is fairly straightforward in that the boring head has a calibrated dial on the side. Measure the hole you just cut, and dial in the amount of increase in 0.001-inch increments. Tighten up the setscrews and have another go. Again, there’s a lot of www.kitplanes.com

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The traveling rest gets its name because it travels in the X direction with the cutting tool, and supplies a “rest” to resist any motion of the material in the Y and Z directions.

extension here, so don’t try to take quarter-inch-deep cuts; 0.010 inch at a time is usually safe. It’s for these reasons that I recommend that you practice a bit with this tool by cutting a few circles in something soft such as PVC. Wood usually leaves too many splinters, so plastics are better. Lest you feel that this is a wimp’s way, commercial shops frequently use stabilized plastics to test tool paths, feeds, speeds and the sequence of the operations before cutting into expensive materials.

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The Traveling Rest The traveling rest is not a self-contradiction; it’s a can’t-do-it-without-it accessory that lets you turn a long, skinny rod into a skinnier one of a consistent diameter. First off, steel bends. To cut steel on a lathe, or any other material for that matter, you have to shove a sharp edge against the surface of a spinning material. If the material you’re cutting has a lot of cross-section to resist the shove, you’re OK. But if it’s relatively skinny, it’s going to move away from the tool. As the point of contact moves farther from the supported end of the material, the material will move even farther out of KITPLANES February 2008

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Home Machinist, Part 11 continued its relaxed position. What we have to do is support the material so that it doesn’t go where it wants to. “Oh come now,” you’re saying. “Steel won’t flex that much.” To illustrate my assertion, I set up a ¾-inch steel rod in the lathe, extended it about 5 inches beyond the jaws, and took a cut 0.005 inch deep. The song of the harmonic was not quite as loud as my neighbor’s oversped Bonanza on takeoff, and the surface finish was, well, interesting. Then I set up the traveling rest and voila: silence and chips that could be used on a Heavy Metal Shirley Temple doll. Obviously, cutting takes a lot of force to bend that length/diameter of steel. So what’s going on? A moment’s cogitation will reveal that your cutting tool

To illustrate the use of the traveling rest, I made a cut without it. Only 0.005 inch into the material was enough to generate a harmonic chatter on a ¾-inch steel rod.

is being pushed horizontally into the material, and, because the material is rotating, it wants to climb up onto the

Without the traveling rest, these nice, continuous chips are not possible. They’re draped over the toolpost just for illustration purposes.

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tool. As a result, we need something to brace the material in two directions. The traveling rest, with its two bronze points, is just the ticket. Mounting it is simple enough: Loosen the locks, back out the two points, position it as close as possible to being opposite the cutting tool, and then clamp it onto the cross-slide. Now screw the two points in until they lightly touch the material. I say “lightly” because we don’t want to shove the material toward us, just prevent it from moving away from the tool. “Points” is not a very accurate description. The tips are cylindrical for obvious reasons, but cylindricaladjustable-load-bearing-surfaces is a bit unwieldy, so I’ll stick with points. While it’s as obvious as dawn trying

It can be seen here that the traveling rest is positioned right against the material and moves in the X direction with the cutting tool.

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With the traveling rest attached to the cross-slide, you obviously cannot use the cross-slide (the wheel below my wrist) for repositioning of the cutting tool.

to sneak past a rooster, I’ll point out that metal-on-metal needs lubrication. A finger-dab of axle grease works just fine. Just don’t use too much or you’ll wear it when you turn on the lathe. And resist the temptation to reapply the old grease—it can get hot. Prior to using a steady rest, you’ve probably used the cross-slide for adjusting the depth of the cut. What’s not so obvious is that it won’t work here; you’ll move the cutting tool in at the same time you back away with the points. The solution is simple: Turn the compound slide around so that it goes straight into the material, and take your readings from its dial. The other “Oh, yeah, now I see how it works” revelation is that with every cut you have to add a bit of grease and readjust the points. On my machine I’m not able to position the points directly opposite the cutting tool; they lead the tool by about half an inch. This means that the points are not supporting the material for the last of the cut, thereby allowing diameter control to go to garbage. In this instance, though, I wanted to cut off the material to a 4-inch length and then turn down the end so it could be threaded, so it was no problem. Just plan ahead. Other ways of stabilizing material that extends well KITPLANES February 2008

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Home Machinist, Part 11 continued beyond the chuck include the steady rest, live centers and dead centers. We’ll tackle those next month.

FAQs In closing, I’d like to address a couple of issues brought up by readers. Several of you have written asking why I seem to love three-in-one machines. I don’t. When I bought mine it was the best option for the available space. I was building in a two-car garage that had even less wall space than a singlecar garage, because I shared it with one car, three “person” doors and one garage door. Would I buy it again now that I have more space? No. I’d get a good desktop milling machine and a nice lathe. Why? It’s easier to jump from one machine to the other or leave a machine set up for additional work. Secondly, I was taken to task for suggesting that cutting tools could be disposed of rather than resharpened. The writer was rather vehement in extolling the use of a greenstone wheel, a sort of precision grinding wheel that works on extremely hard material. Although a greenstone wheel is a very good way to touch up a dull tool, you have to have a lot of dull tools to make it cost effective. And even though it doesn’t require a lot of space, it does require a bit of skill. Further, as I said at the top of this piece, this is a beginner’s class, and we have to take our time. As the physicist John Archibald Wheeler noted, “Time is what prevents everything from happening at once.”

Just a little wheel-bearing grease works well to minimize wear.

Editor’s note: If you have specific questions for author Bob Fritz, or if you have certain projects you’ d like us to cover, email us at [email protected] with “Home Machinist” in the subject line. 

Look at the circumferential line that the arrows are indicating. During the cut I backed off the horizontal bronze point. That let this 0.75-inch steel bar move laterally, and the diameter of the cut changed. A lot of force is involved.

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