BENDING METAL |
GETTING STARTED |
There seems to be two schools of thought on setting up for building, and both seem to give good results. This is what works for me.............I like a good, solid work table that I can climb on, kneel on, lean against, kick and swear at when things don't go right, bruise my aching bones on when I run into it, and generally give me a work area I can depend on to give me a flat solid place to build good components on. I started my table with 4 sheets of 1/2" plywood and half a yard full of 2x4's. Built a 2x4 frame on a flat floor, just under 4' x 16', split 1 sheet of plywood in 1/2 to make 2 - 4'x4' pieces. A full sheet went in the center of the frame, with a 1/2 sheet on each end. Then 2 full sheets end to end on top. A couple of fistfuls of sheetrock screws anchored the whole thing to the frame. Then hoisted it up onto saw horses to support it, while I figured a comfortable work height. For me, that was just under waist height. Eight ( 8 ) 2x4 legs went under it, then used pieces of cedar shims from Home Depot, along with lengthwise, and diagonal strings, and a bubble level to make sure the whole thing was flat, level, and square. Didn't want any twist built into my flying surfaces. When time for covering came along, I found that the construction grade plywood was real good at hooking threads out of the fabric. No, no, no, no ! ! ! So, I faced it with a 1/8" sheet of masonite. I realize many will disagree with me, and you're welcome to it, but I feel good about this, and it worked well for me. I also can't see the point of scrimping to save $10.00 on the area I'll use to build a $30,000.00 airplane. ( I never dreamed it would even come close to that, but.............) When finished, I'm going to hang my precious ass in that thing, and commit aviation, and I want it RIGHT ! ! ! YEAH ! ! ! |
Possibly I'm wrong here, too, but I wanted at least a moderate amount of precision, and the same for repeatability, so I built jigs on the table for each PAIR of components. ( Yeah, yeah, except for single items like the rudder.) By building jigged pairs simultaneously, I could cut 2 pieces at a time, and compare as I built. If I made a small mistake on one piece, I'd make the same mistake on the other, and at least they'd be balanced on the plane. 'Course, if I boo-booed, ( and I did - repeatedly ) then 2 pieces were bad, instead of 1. Usually those pieces could be used somewhere else. Then too, I eliminated any worry about the possibility of building 2 lefts or 2 rights. I'm told this happens surprisingly often. |
For cutting the tubing, never use a tubing cutter with a wheel. Leaves a strong burr on the inside that's hard to clean out. Also........NEVER.........NEVER.......mark aluminum with a pencil. Opinions vary as to just what exactly happens, from electrolysis to scratching, but believe me, it will damage the aluminum, and it will give you problems later. Regular ball point does fairly well, but an extra fine point felt tip is perfect, and easy to clean up. Lesson from Lar................don't use the pens on powder coating - it soaks in and is nearly impossible to remove. How do I know ?? ...........?? Sorry guys, I used a pencil on the powder coating, but Never on al. Cut the tubing with a 32 tpi hacksaw. Support it in a vice with soft jaws made from scrap aluminum, or left over al angle. Clean and square the end on your handy 24" bench mounted belt sander - I absolutely can't concieve of building anything without one, and they only cost $90.00 to $150.00. To clean the burr out of the inside of the tube, I used a large drill bit. Works fine, but recently, I was given a set of countersinks with a removeable wooden handle. What a joy ! ! ! Do I ever wish I had thought of them 4 years, and 30 million burrs ago. Weeeellll............almost. |
With care, you can make large radius bends by hand. For tighter radius bends, I used a 3 in 1 tool from A/C Spruce, ( p/n 368-FH ) and never regretted the price. Handy, rugged, and does a beautiful job. I quickly found that 6061T6 tube will bend quite well, though it's very hard. Once bent, it will NOT unbend. On a scrap piece, make a 90 deg. bend. Then try to straighten it back out. Uh Uh........it'll break. Same as compressing the ends of ribs where they'll rivet to the spars. Flatten them too much, and they'll crack. Then throw them away. |
I used my belt sander to smooth out the end of the jaws of an old pair of vice grips, to flatten the ends of the tubing. Then rivetted my ribs to the TOPS of the trailing edges of the control sufaces, and bitterly regretted it later, when it came time to cover them. What a miserable job, wrapping all those little bumps. I really recommend following the tip to bend the end of the ribs, so that they fit INside the trailing edge tube. Leaves a smooth edge that's much easier to cover. I think it looks better too. Oh well. |
I've found 3 major types of drill bits, and do they ever make a difference. The top picture shows a standard drill bit. Uh........cobalt drill bit...........very worth the extra price. The top bit is useful for most work, especially in steel, especially in 4130 steel. Hmmmm.......now, where have we seen that ?? For most work, the standard cobalt bit will do a fine job, and if you keep the heat down, will last a LONG time. This may cause a war again, but in my experience, keeping the speed down, and the pressure up, will really benefit the drill bit. An old machinist friend tells me that this keeps the bit cutting well in cool metal, which cools the bit. The bigger the bit, the more pressure you need. Ease off the pressure, or run up the speed, and the bit starts spinning more than cutting, and heat goes up. End of bit. Please keep in mind that this must be tempered with reason - if you really mash down on a small bit, you'll have problems - at the very least, gouging the metal. Likewise, going thru aluminum, and to a lesser extent, steel, heavy pressure will cause a huge burr on the exit side, that MUST be trimmed. With practise, you'll feel the bit cutting. |
Before drilling, you Should center punch the mark to assure an accurate location. Drill bits love to wander around and make interesting patterns in your tubing. I use a General Hardware #79 snap punch to start the mark. Bought mine at Home Depot for around $20.00. They also sell a sexy looking one with a red wooden knob for about the same price. Don't be fooled, they're junk - get the General. Once again.......how do I know ??...........Guess ! ! ! A snap punch mark is pretty small, which brings us to drill bit #2, the center one in the pic. This is a Black & Decker " Power Point." The small extension on the tip acts as a starter bit, and easily picks up the snap punch mark. If you're uneasy, or it's a critical part, use a center punch and hammer to enlarge the snap punch mark. Take it easy ! ! ! I have 3 hammers out there, and 95% of the time, the little 6 oz. ball peen is all I need. Once in a while, I'll use the 16 oz carpenter's hammer, and I don't recall ever using the 3 # single jack - on the airplane, at least. The power point bit is great in aluminum, and will last fairly well. It won't hold up for long at all in steel. Gets expensive. The bottom bit is an Irwin bit that I buy at an auto parts store. For want of a better name, I call them a "shrouded tip," because the cutting edges are almost down to the tip. These are so delicate, that for a while I thought the tip was diamond or something grafted on. After not too many holes, the tip will break off, and "skate," making a mess of things. For this reason, I only use them for 1 purpose.............they are perfect for such jobs as the holes for control surface hinges. For these, I drilled the hinges, then located them on the ailerons, elevators, etc. with jigs. The problem is, when drilling the hole in the tube under the hinge, where is the exact center of the hole in the hinge ?? If you're not right on the money, one or both holes will be ovalled, making for a poor grip with the rivet. The shrouded tip bit will locate itself in the existing hole, and make an accurate hole in the tube underneath. Works great, but they don't do well at all in steel. |
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