.
It's not much of a trick. But then, it's not much of an air brush. $4.99 from Harbor Freight. #6131. Little jobbie made in Taiwan, but not very well. Made, that is. Oh, it'll blow paint. Any airbrush will blow paint.
Air brush is a syphon-type spray gun. The paint is in a little screw-top jar that plugs into the gun. The gun is about the size of a ball-point pen. The jar has a hole in the lid so the thing is open to the atmosphere. The jar hangs under the nozzle of the gun. To make it blow you press a little button on the gun. Air blows across a tiny orifice positioned in the throat of a venturi. The orifice is actually a needle valve but we'll get to that in a minute. A suck-up tube runs from the orifice down into the jar of paint. When Mr. Bernoulli reduces the pressure on the venturi-end of the suck-up tube, atmospheric pressure pushes the paint up the tube and out the orifice, where the stream of air blowing past atomizes the paint and blows it out the end of the gun. So mebbe we should call it a push-up tube.
There's not much in the way of control. The paint comes out in a circular pattern, about the same as you'd get from a spray can. And while you can't control the shape of the pattern, you can control the size of the pattern. You can also control how much paint you deliver by adjusting the air pressure. Plus, you can thin down a thick paint, lay it on in thinner coats. Or leave it thick. Air brush don't care. Thick stuff just takes more air pressure. And comes out in bigger particles. Air brush will spray molasses if that's what you want to do.
So there you are with this itty-bitty spray gun. Jar only holds two ounces. If you're an artist, you buy a lot of jars, fill them with different colors of paint; Keep on Trucking and all that sort of thing. To spray a different color you unscrew one, screw on another, after flushing the suck-up tube in a jar of thinner in between. Just open up the needle valve to flush it out good.
Of course, two ounces isn't a very useful amount, not if you're building airplanes. But just as artists use different bottles, so can you. Larger ones.
I use gravy jars. Heinz. Usta have 57 Varieties. Gravy jar holds about six ounces. I tried Spanish olive jars for a while but they didn't have the right wrist action. Some buys use baby food jars but I've become a confirmed Gravy Jar Man. You can't use a really fat jar because the air hose screws on to the bottom of the gun and gets in the way. But you can use a tall skinny jar, which is what I did during my Spanish Olive period.
MAKING A BIGGER JAR
Got a 7mm deep-socket? Take the air brush jar apart. No, not the gun, the JAR. You'll have to pull the suck-up tube off the fitting. If it's stuck, heat it. Don't damage it, you'll need it later. Once the tube is out of the way use your 7mm deep-socket to loosen the nut holding the suction tube fitting to the lid. Take it apart and keep track of the washers.
Got a Unibit? A Unibit makes drilling holes in thin stock a breeze. Your new lid is thin stock. Drill a pilot hole for the Unibit then open it up to accept the air brush fitting. It's about 6mm in diameter, which is close to 1/4" so try that.
While you're drilling, put a #60 hole in the lid out near one edge. That's your vent, the thing that lets those fourteen point seven pee-ess-eyes push the paint up the suck-up tube.
Now put your new lid together. Transfer the hardware from the air brush lid to your Gravy Jar lid. Make sure the vent hole is at right angles to the outlet of the suck-up tube. If you don't, you'll end up spilling paint all over yourself. (At 90 degrees from the axis of the spray gun, the vent hole will always be near the apex of any tilt you put on the bottle. If you position the hole anywhere else, there will be some tilt-angles you can't use.)
Your bigger jar will need a longer suck-up tube so go punch a hole in a used spray paint can. Let the residual propellant escape then cut the bottom off the can. Inside you'll find a free marble (!) and a length of suck-up hose about 7" long. That's too long for your Gravy Jar but you can cut it down. Except it's also too big around - it won't fit on the suction fitting in the lid. Metric vs whatever and all that. So go find the original air brush suction tube. Snip off about half an inch and slide it onto the suction fitting. Now slide the spray can tube over the smaller air brush tube. It won't want to go but it will, if you heat the larger tube and put a little muscle into it when you slide it on.
Why the tube out of a spray can? Because you need tubing that will withstand MEK and toluene and lacquer thinner and whatever else you might use. You can buy such tubing but the minimum quantity is about five feet and it costs the earth. And there you are, with half a dozen useful lengths of the stuff inside old spray cans. Plus, you get a free marble.
So how long does it have to be? It should reach the bottom of your Gravy Jar. Not smack up against it, but pretty near. You'll also need several extra jars plus one extra lid. (Why an extra lid? Because you've just converted one of them to your sprayer-lid.)
That takes care of making your new lid, which is 90% of the job. But like everything in homebuilding, the remaining 10% of the job will take 90% of the time.
MAKING IT USEFUL
See that crappy little black plastic air hose that came with the air brush kit? It's going to pull off its fittings about ten minutes after you start using the thing. So go find some fine stainless steel safety wire, put a couple of warps around the fittings and twist them tight. Po' Boy hose clamp. Works, too. Snip off the twist and tuck the end flat. A bit of tape over the safety wire will keep you from cutting yourself. (And yes, that does happen to be a Band-Aid on my airbrush hose. No, I don't want to talk about it.)
The air brush kit comes with a fitting that connects to cans of compressed air (!) Seriously. They sell canned air at hobby shops and the like. They don't hold much air but if you're painting toy trains or model airplanes, you don't need much. For painting real airplanes, on the other hand, you need a buncha air. Mebbe two bunches, before you get it all done.
To provide air to the spray gun you need to buy an adapter that will mate with the fitting on the hose in the kit. Harbor Freight sells one, #P-1655. It's got a male thread on one end to match the fittings on the air brush, and a female 1/4" NPT on the other. To make it match my air line I added a quick connect. Harbor Freight sells those too but I don't know the number.
The 1/4" airline adapter (P-1655) allows you to use your air compressor. Or any other source of compressed air that has a 1/4" NPT fitting hanging off the end. Such as a big tank of air for refilling a tire. Which will blow more paint than one of those itty bitty cans from the hobby shop.
The air brush is sensitive to air pressure. If using canned air, the lid has an adjuster built in. But when using an air compressor, air tank or whatever, you'll need to get yourself some form of pressure control in the line. Most of the time you'll only need five or ten pounds but with thick stuff you will need as much as 90 psi. Because the gun is easy to adjust you can get by with a very simple restriction-type ‘regulator.' (It doesn't do much regulating but it does cut down the pressure.)
IS THIS REALLY PRACTICAL?
That depends on your financial situation. Sixteen ounce rattle can of ZC primer only has about seven ounces of paint. That makes it pretty expensive. Plus, the nozzle is always clogging up and every time you want to use yellow all you got is green or visa versa.
Quart of primer contains a quart of primer. Cut it 1:1 with reducer, you got two quarts. That's sixty-four fluid ounces and that works out to about one eighth the cost of using rattle cans.
And then there is other stuff to paint, such as steel parts, which get a baked coat of primer then a baked coat of gloss black or whatever. Having a little spray gun that's easy to set up and simple to clean makes blowing a little paint quick and inexpensive. It takes about a minute per rib to give them a coat of ZC with the air brush.
SPARE PARTS
At five bucks a copy you can be pretty sure your airbrush won't outlast the Pyramids. And it is going to accumulate some wear. It's got a couple of teenie tiny O-rings that probably won't cost more than ten dollars each, plus the hernia you'll get from digging through the McMaster-Carr catalog trying to find them.
So buy two kits. The second is to provide spares for the first. At five bucks a pop it's the logical way to go.
USE, STORAGE & CLEANING
Get yourself a box about a foot on a side. Cardboard is okay. Give it a coat of paint; mebbe stiffen it up with some stringers. Use it to store your Air Brush Kit. Keep the thinner and spare jars and spare parts and stuff like that in the box, along with your pipe cleaners.
One of your jars should be filled with thinner. Lacquer thinner will do to clean up after most primers. The other jars are filled with whatever you want to spray, from kerosene to zinc chromate. To give the glass jars a bit of protection, wrap them with several turns of old fashioned friction tape – the rubberized cloth stuff.
Store your pre-mixed primer, tightly sealed, in the refrigerator. If you've got kids in the house, store the stuff in an ammo can out in the shop. Keep it on the concrete deck, covered by several layers of cardboard to keep the stuff cool.
Every time you use your spray gun you gotta clean it. Takes mebbe five minutes, tops. Here's how.
Unscrew the paint jar, put the lid on it and put it back in the refrigerator. Plug your sprayer lid into your jar of thinner and blow thinner into a rag or can until the suck-up tube and nozzle are clear. Get a little thinner on a rag and find your pipe cleaners. Dip a pipe cleaner in thinner and have it ready.
Shut off the air, disconnect the hose and put it away in the storage box.
Take a look at the gun. See that little circlip? Open up the screwdriver blade on your jackknife and pry off the circlip. Now you can push the brass needle valve down through the body of the gun. Unscrew the needle valve as you go. The cone of the valve stays on this side, only the needle part pushes down & out of the gun. Unscrew the nozzle.
That's it. Three parts. Four, if you include the circlip.
Use your pipe cleaner to ream out the needle valve and the nozzle. Get ALL the paint outta there. Use the rag to wipe any paint off the suck-up tube and sprayer lid.
Once everything is clean, put it back together and store it in the box.
MAKING A SPRAY BOOTH
The last part of your spray-paint kit is the spray booth, which looks suspiciously like a cardboard box. Hang it or nail it near to a window and rig some dryer ducting from the box to a panel in the window – you want those fumes to end up in the neighbor's air conditioner intake, not in your shop. Rig a small fan to pump air out of the booth and into the ducting. In case you hadn't noticed, a fan is an air pump. To make it work like a pump wire & tape it to the wall of your spray booth. On the outlet side, rig a plenum chamber (which also looks suspiciously like a cardboard box) and fasten your ducting to the plenum chamber.
Making a spray booth is one of the few times in your life when you can use duct tape on a duct. Enjoy.
You don't need a very big fan because you aren't using a very big spray gun. The boxer fan out of a computer power supply will work but most of them run on 12vdc and are noisy. I use a cheap (cheap!!) import desk fan, about six inches in diameter.
To make cardboard useful it needs to be stiffened with wooden stringers. Lath will do fine. Use urethane glue and staples. Once the glue cures, give the box a coat of white house paint and repaint the interior periodically, not only to renew the white surface but to bind up any over-spray residue. After you finish your plane, cut the box up and get rid of it.
When adding stiffeners to your spray booth, be sure add a couple to the inside, up near the top of the box. Rig a couple of wires up there. To paint stuff you'll typically hang it form hooks of bailing wire and use a wand of the same stuff to hold the part in position while you shoot it with paint. Most primers dry in a matter of minutes but it's a good idea to rig a curtain on the front of the box so you can leave parts hang while they dry. In a cold or damp climate, adding a door and a couple of light bulbs NEAR THE BOTTOM will turn your spray booth into a drying booth.
The spray booth is to keep from blowing toxic residue all over your shop. Everyone worries about hexivalent chromium but the truth is, alkyd and epoxy resins, when in aerosols, are just as bad for you, although for different reasons. So even though you have a spray booth that passes your problems on to the neighbors, any time you blow paint you should dress for the occasion. That means an air mask or industrial quality respirator, and gloves that are impermeable to the thinner & vehicle in whatever paint you're spraying. (And this applies to rattle cans as well.)
Most volatile vapors are explosive. Try not to weld while painting, nor to paint while welding. And the smoking lamp should be out.
PASSING YOUR PROBLEMS ALONG
Back when Tony Bingelis was painting his Falco one of his neighbors complained about the smell. I told him he didn't have a big enough cat box.
The average cat box is 20" long by 14" wide. So you build a box 20-1/2" long by 14-1/2" wide by about 30" tall. The box slides down over the cat box, which is four inches deep and contains 2" of water. Inside the box you've built, there are five partitions spaced about 3" part, except for the input and output which are about 4". Two of the partitions are open at the top but extend down INTO the water. The other three partitions are sealed at the top but only extend downward to within one inch of the water.
Any place you need to form an air seal, such as along the edges of the plastic cat box, cut up some urethane foam, give the surface a spritz of upholstery glue and stick it to it.
On the output of your cat box you put a large fan positioned to suck air through the box. The inlet is on the top of the box at the far end.
What you've just built is a kinetic air filter. Each time the air is forced to reverse direction, which it must do to negotiate the partitions, heavier particles will tend to collide with the surface of the water and stick there.
Even a one cat box unit is surprisingly effective at eliminating odors and trapping paint particles. But if one unit isn't enough, add another to either end. When combined with a labyrinth filter at the input (ie, a stack of furnace filters) and an electrostatic particle precipitator on the output, you can get clean room conditions with only seven reversals (ie, a two cat-box unit).
If you rig such a unit for your spray booth the odds are your neighbors will never know when you decide to blow a little paint, since none of it – nor any of its vapors – will get out of your cat box.
The Cat Box Principle also applies when painting the entire airplane. Rig an air dam across the garage so the door comes down onto the dam and install the cat box in the middle. Seal up any gaps with cardboard, foam and duct tape. To get a flow of air into the shop, use a window or door on the opposite side of the shop. Build a light frame of wood to fill the doorway or window. Glue furnace filters to the frame. Put the frame in place any time you want to blow paint. It won't stop a sand storm but it'll keep out the bugs and most dust.
A WHIFF OF REALITY
So you go down to the local EAA chapter and tell the folks about your nifty little air brush and your cardboard spray booth and your cat box air filter... and everyone will tell you what a bad idea it is. Spray cans are better. Zinc Chromate is evil incarnate. And if you use 6061 and pop rivets you don't need corrosion protection, or that noisy air compressor or all that other stuff. Besides, if the designer wanted the part protected, it would have arrived that way IN THE KIT.
About there I realize I've stumbled in to a meeting of the Dunkin Donut Kit Assembler's Association and slink back to the shop to continue making curvy bits out of flat bits. And giving the curvy bits a spritz of ZC when I get them done, because, not having a zillion dollars for a kit (or even $10,000), I've no idea how long the part will sit on the shelf before it can be assembled. That spritz of ZC will keep it from going bad. What I do know is that building a Teenie Two will cost me about $500 and a CH-701 about $1,000 (less the engine in each case), because I'm only paying about two bucks a pound for the materials, right down to the solid aircraft rivets, gleaned from various surplus sources at scrap metal prices.
Which is why a $5 spray gun and cardboard spray booth and cat box air filter make good sense to me. An' besides, I get a free marble.
-R.S.Hoover
Tuesday, November 21, 2006
AV - Cutting Stringers
In a related thread (Cutting aluminum etc) 'Jim in NC' reminded us of the need for an auxiliary shoe when cutting thin stock on a table saw.
This also applies to cutting stringer stock.
Although you may order spruce stringers cut to size, if you buy a spruce 'kit' the stringer stock will usually arrive as a number of six-inch planks finished to the required thickness. You are expected to set up your table saw to the second dimension and rip the planks.
The standard shoe (ie, the removable panel through which the saw blade extends) allows too much clearance for the cutting of 1/4" and 5/16" stringer stock on a production basis. You must either make up a new shoe or use an auxiliary shoe in the manner described by Jim. I think the use of an auxiliary shoe is the more common procedure since the cutting of stringer stock also dictates the need for finger-boards and the like. (Using an auxiliary shoe allows them to be fastened to the shoe.)
As with the sawing of aluminum, ripping stringer stock is a procedure common to the business of building airplanes. Unfortunately, the success of many such tasks depends on a host of details largely unknown to the novice yet seldom mentioned in the literature. Experienced builders tend to forget that a novice must be told everything, such as the need to dress for the occasion when sawing aluminum... or that a jig is needed when cutting a scarf joint, a zero-clearance shoe when cutting stringers and so on.
Jim's message caused me to recall a comment by a local builder about having to buy finished stringer stock because he was unable to accurately rip a quarter-inch plank into quarter-inch square sticks for his ribs. The builder was an experienced wood worker but looking back on it, I suspect he didn't realize he'd need an auxiliary shoe for cutting such small stock.
-R.S.Hoover
This also applies to cutting stringer stock.
Although you may order spruce stringers cut to size, if you buy a spruce 'kit' the stringer stock will usually arrive as a number of six-inch planks finished to the required thickness. You are expected to set up your table saw to the second dimension and rip the planks.
The standard shoe (ie, the removable panel through which the saw blade extends) allows too much clearance for the cutting of 1/4" and 5/16" stringer stock on a production basis. You must either make up a new shoe or use an auxiliary shoe in the manner described by Jim. I think the use of an auxiliary shoe is the more common procedure since the cutting of stringer stock also dictates the need for finger-boards and the like. (Using an auxiliary shoe allows them to be fastened to the shoe.)
As with the sawing of aluminum, ripping stringer stock is a procedure common to the business of building airplanes. Unfortunately, the success of many such tasks depends on a host of details largely unknown to the novice yet seldom mentioned in the literature. Experienced builders tend to forget that a novice must be told everything, such as the need to dress for the occasion when sawing aluminum... or that a jig is needed when cutting a scarf joint, a zero-clearance shoe when cutting stringers and so on.
Jim's message caused me to recall a comment by a local builder about having to buy finished stringer stock because he was unable to accurately rip a quarter-inch plank into quarter-inch square sticks for his ribs. The builder was an experienced wood worker but looking back on it, I suspect he didn't realize he'd need an auxiliary shoe for cutting such small stock.
-R.S.Hoover
AV - The Skin Game
.
Working out back of the shop under the shed roof. I'm cold and in a lot of pain. Khaki's, flannel shirt & a shop apron was warm enough when I started, afternoon sun heating up the tin roof. Not too bad at all. Except for the pain, which I pretend not to notice. Then the sun did it's trick and the breeze picked up. Eight to ten miles per hour according to the homemade anemometer spinning busily above the shop. But it's been known to lie.
California cold isn't really. Nothing at all like Duluth cold or Fairbanks cold. But I've been bent over the bench about four hours now and the pain is becoming The Pain. Kidney stone; something new for me. (If you haven't been there, you won't even come close :-)
A jacket helps. As does a cuppa coffee. But when I go back out to the shop the wind has picked up and spates of rain are coming in from the coast, invisible now, all light gone from a sky filled with dark scudding clouds. But no pills. Not yet. Not until I finish deburring the holes I've spent all afternoon laying-out and drilling.
Wing skins. Not big; two by eight feet, plus some trim. Outboard wing panels, upper surface. Only nine ribs. No stringers. But a lotta holes.
The holes for the spars reside in a couple of pieces of eighth-inch by one inch drug-store aluminum, the holes for the ribs are in a yard stick hijacked as a template. I used the computer to lay-out the holes, pricked the bullets, center punched the prick marks, drilled them on the drill press with the bit spinning 3100 rpm and the swarf winding away in a spiral as bright as a diamond. And then deburred.
The skins, left and right, stuck together belly to belly with a few squirts of spray glue, are laying on an old door pieced out with some scrap. The trim allows a couple of free holes to accept the cleco's that fasten the skins to the table.
Layout is school-boy geometry. Stretched black thread for my X, carpenter's square for my Y, corners trammeled with a twelve-foot piece of extruded angle, the intersections carefully marked with a Sharpie. I can live with plus or minus sixty but smile when the marks cross each other with an error of perhaps fifteen thou in 98.95 inches. Close enough.
The ribs have a riveting flange five-eighths of an inch wide with the Safe Zone being the middle third. For a safe structure the AN3 flush-heads should end up somewhere within a square about three-eighths inch on a side. But closer is better which is why I use templates for laying them out. Centered on the line then squared, the holes fall almost perfectly within a square only an eighth of an inch on a side. This is good. This is why I've spent four hours bent over the bench with the wind blowing up my ass. (Should of put on the jacket sooner. Should have bought Xerox in 1957... )
Once located relative to the line of holes for the spar cap rivets, the rib template is cleco'd to the panel and the twenty-six holes are drilled. The swarf is brushed away, the template moves to the next rib, the location is verified (BIG red arrows, hard to miss... but not impossible) and you do it all over again. Not a big deal. But the culmination of prior work spanning months.
After drilling comes deburring. Then flipping the panels over and deburring again. Dog-leg deburring tool, finger as a gauge. The skins are sixteen thou. Gotta be careful with the deburring, keep the skins supported. They'll be dimpled later and it's tough to get a burr out of the bottom of a dimple.
The only secret to building airplanes is to do something every day. Doesn't matter what you do or how long you do it, what matters is the work-habit. Do something every single day and you'll be surprised how quickly you run out of things to do. When that happens the only thing left is to climb in and go for a ride.
Today it was some holes in the wing skins. Tomorrow it will be something else but today is past and the holes are done and I get to come in the house and gobble a handful of pills and feel The Pain crawl back in its cave.
It's raining now but the coffee is hot and the pills have kicked in. Just another day in the solitary art of Flying Machine construction.
-R.S.Hoover
Working out back of the shop under the shed roof. I'm cold and in a lot of pain. Khaki's, flannel shirt & a shop apron was warm enough when I started, afternoon sun heating up the tin roof. Not too bad at all. Except for the pain, which I pretend not to notice. Then the sun did it's trick and the breeze picked up. Eight to ten miles per hour according to the homemade anemometer spinning busily above the shop. But it's been known to lie.
California cold isn't really. Nothing at all like Duluth cold or Fairbanks cold. But I've been bent over the bench about four hours now and the pain is becoming The Pain. Kidney stone; something new for me. (If you haven't been there, you won't even come close :-)
A jacket helps. As does a cuppa coffee. But when I go back out to the shop the wind has picked up and spates of rain are coming in from the coast, invisible now, all light gone from a sky filled with dark scudding clouds. But no pills. Not yet. Not until I finish deburring the holes I've spent all afternoon laying-out and drilling.
Wing skins. Not big; two by eight feet, plus some trim. Outboard wing panels, upper surface. Only nine ribs. No stringers. But a lotta holes.
The holes for the spars reside in a couple of pieces of eighth-inch by one inch drug-store aluminum, the holes for the ribs are in a yard stick hijacked as a template. I used the computer to lay-out the holes, pricked the bullets, center punched the prick marks, drilled them on the drill press with the bit spinning 3100 rpm and the swarf winding away in a spiral as bright as a diamond. And then deburred.
The skins, left and right, stuck together belly to belly with a few squirts of spray glue, are laying on an old door pieced out with some scrap. The trim allows a couple of free holes to accept the cleco's that fasten the skins to the table.
Layout is school-boy geometry. Stretched black thread for my X, carpenter's square for my Y, corners trammeled with a twelve-foot piece of extruded angle, the intersections carefully marked with a Sharpie. I can live with plus or minus sixty but smile when the marks cross each other with an error of perhaps fifteen thou in 98.95 inches. Close enough.
The ribs have a riveting flange five-eighths of an inch wide with the Safe Zone being the middle third. For a safe structure the AN3 flush-heads should end up somewhere within a square about three-eighths inch on a side. But closer is better which is why I use templates for laying them out. Centered on the line then squared, the holes fall almost perfectly within a square only an eighth of an inch on a side. This is good. This is why I've spent four hours bent over the bench with the wind blowing up my ass. (Should of put on the jacket sooner. Should have bought Xerox in 1957... )
Once located relative to the line of holes for the spar cap rivets, the rib template is cleco'd to the panel and the twenty-six holes are drilled. The swarf is brushed away, the template moves to the next rib, the location is verified (BIG red arrows, hard to miss... but not impossible) and you do it all over again. Not a big deal. But the culmination of prior work spanning months.
After drilling comes deburring. Then flipping the panels over and deburring again. Dog-leg deburring tool, finger as a gauge. The skins are sixteen thou. Gotta be careful with the deburring, keep the skins supported. They'll be dimpled later and it's tough to get a burr out of the bottom of a dimple.
The only secret to building airplanes is to do something every day. Doesn't matter what you do or how long you do it, what matters is the work-habit. Do something every single day and you'll be surprised how quickly you run out of things to do. When that happens the only thing left is to climb in and go for a ride.
Today it was some holes in the wing skins. Tomorrow it will be something else but today is past and the holes are done and I get to come in the house and gobble a handful of pills and feel The Pain crawl back in its cave.
It's raining now but the coffee is hot and the pills have kicked in. Just another day in the solitary art of Flying Machine construction.
-R.S.Hoover
AV - Making Boxes & Things
Guy come by the shop last weekend. Wanted me to make him the slider dingus that goes inside the short strut on a Cuby landing gear. No plans, just a badly done sketch.
"What's it made out of?" I ast him. He didn't know, guessed it was steel. "What kind of steel?" I ast him. Blank stare.
I went out to the little shed, chased the possoms off the top shelf, found the CUBY file box, pulled it out. He'd followed me, stood at the door acting like he's never seen a possom before. Or a stack of blueprint filing cabinets. The Cuby plans weren't in the cabinet. Like most plans they have their own box. He helped me put the V77 box back on the shelf then followed me back to the shop.
Dingus was shown as steel, no alloy specified. It's not a very good drawing. (Drawing reference about 18-D) I flipped through the plans looking for a more detailed drawing but don't find one. Which doesn't mean it ain't there.
The dingus is properly called the ‘slide' and acts as the carrier for the AN4 bolt that is the travel-limiter on the Cub's gear. It goes inside the short strut, which is 3/4 x .058 so the OD of the dingus is called out as five-eighths, which should work. Drawing shows it as being just half an inch thick with a significant chamfer, which won't work, unless you've got some dimensions to go by. I point out the missing dimensions which makes the existing dimensions questionable. He waves a lot of money at me and I am wooed into making him a couple of dinguses (denguii?).
The guy quickly lost interest in watching me set up the lathe, started nosing around the shop, which I don't like. People steal things. Even nice people like fellow pilots, or rich people like most homebuilders. (Yeah, I know. Richer than me, though.) I sat him down in the patio and gave him the set of plans to play with while I made his dinguses.
I didn't have any five-eights rod but I had a stub of free-machining three-quarter stock so I used that, turned it down to .625. I made the dingus five-eights in length with a sixty-thou chamfer on each end. Drawing said the quarter inch hole was drilled, which would probably work in most cases, so I laid them out, set them up in a vise on the drill press, piloted them to something smaller then opened them up with a freshly sharpened quarter-inch bit. Broke the edges, buffed them up, tried them with an AN4... kinda tight but good enough for a Cuby.
He admired the shiny little slugs of steel then tucked them in his pocket and asked, "Did you make this?" flapping the lid of the plans-box back & forth like a punkah on the ceiling of a bungalow in Krishnapur.
A plans box is just a shallow plywood tray with a hinged plywood lid. The hinge on this one was a piece of leather salvaged from an old pair of boots. Of course you make them, for crysakes. I just looked at him. Okay, maybe I rolled my eyes or something.
"I've never seen anything like it," he said. Which told me he hadn't been on many construction sites. Or boatyards. Nor built many airplanes. After he left I put some moth crystals in the plans box and put it back in the shed and went back to what I was doing, which has banging a bulkhead out of some .020.
Plans usta be blueprints - blupes. Blupes fade so you store them in the dark. Most modern drawings don't fade but over the course of time needed to finish most homebuilts they tend to get torn, damaged, dirty or lost... unless you do something about it.
Real shops, you've got a filing cabinet for your drawings. And that is one humongous cabinet. When I worked for Vernon Payne he had three of the things, about four by six feet on a side and three feet high with about a dozen drawers in each. Building just one airplane, and working from just one set of drawings, there's no way to justify the cost or space for a flat file cabinet. So you build a flat file BOX. Small box, you can hinge the lid. Big box, as in three by four feet, the lid usually attaches with latches.
What you build it out of depends on you and the night and music. Building a metal airplane? They you'd probably use aluminum. I've made one out of fiberglas but I was just showing off. Mostly, I make them out of wood.
Everybody does this. Don't they?
HOW TO MAKE A PLYWOOD PLANS-BOX
Start with a frame of one-by-two pine. Make the interior about one inch larger than your drawings in each dimension. Assemble the frame using glue and dowels or corner blocking. Don't use any nails; we're going to run it thru the saw later on.
Skin the box with 1/8" luan plywood. If you use staples or brads, pull them out after the glue cures.
Clean up the edges then run the box through the saw ON EDGE so as to cut the one-by-two. As soon as you cut one side, tack some plywood over the cut. Cut all four sides, being sure to keep the same face to the fence so the cut will come out even all around.
Clean up the cut line, clamp the box back together and install a piano hinge opposite which ever side you want it to open. Give it a seal coat of 50-50 varnish:thinner, let that cure for a couple of days then give it a light sanding, wipe down with thinner and lay on a full coat of varnish. If you remembered to varnish under the hinge the thing will be good for about fifty years, give or take a decade or so.
That's the DeLux model. I've got a couple like that but most are more along the lines of a Jeep than a Cadillac. The frame is often pieced out from scraps of 3/4" square stock or whatever happened to be available when I needed to make a plans box. Some use cardboard for the skins instead of plywood, which works okay if you add a few stiffeners and give the cardboard a couple of coats of oil-based paint.
It helps if you start with a frame that is square so use corner clamps if you've got them. But close enough is good enough in this case. Lots of times I use scrap to make up a pair of open trays rather than a box. When I get around to it I clamp them together, true up their edges by running them through the bandsaw then do a few passes against the disk sander. That gives the box a uniform outside appearance and a nice neat edge. Inside, the thing may be crooked as hell but the plans don't know the difference.
The types of hinges I've used range from real hinges, including some aircraft stuff, to anything that has enough flexibility, such as leather or upholstery material. Fabric or leather hinge, you can glue it on if you remember to cover the parting line with tape so as not to glue the box together. If you use brads or screws make sure you have enough depth of wood to provide the support required. Flat belting used to be the first choice for this sort of hinge but you don't see it around much any more.
If you want to make it air tight, run a bead of RTV along the closing line, cover it with waxed paper and leave it closed until the RTV has cured. Then clean things up with a razor. If it's a DeLux version, such as a gun case or whatever, you can route the edge to accept a strand of O-ring stock.
The latch is usually a couple of round head brass brads and a piece of safety wire but anything that does the job is acceptable.
WORKING WITH WOOD
Discovering that every aircraft mechanic needs to be a pretty good woodworker always comes as a bit of a shock to guys wanting to build an airplane out of plastic or metal or steel tubing. If you want to build an airplane - ANY AIRPLANE - and have no experience working with wood, it might be a good idea to get some. Making a box for your plans isn't a bad way to start.
Nowadays, spend a thousand dollars for a good tool, it's liable to arrive in plastic bag. Making small boxes of every conceivable size, shape and strength is a recurring chore for anyone who has a few machine tools because if you just throw stuff in a drawer the odds are it won't be usable when you need it.
THE BEAUTY OF BOXES
Airplanes aren't very heavy. (You wish!) Whole wing's-worth of ribs, metal or wood, only weighs a couple pounds. But bulky and fragile pounds.
Odds are, someone is building the same airframe as you. A good building strategy is to become a part of a group working on the same design. If you can come up with a safe, inexpensive method of shipping stuff back & forth, having one guy do the wing ribs while another does the tail and a third does this and the fourth does that... often saves a lot of time in producing the components.
Parcel Post offers dirt cheap shipping for a container of a given size and weight. Not fast, just cheap. A sturdy plywood shipping container made of pine stringers and eighth-inch plywood is strong enough to protect fragile components yet light enough so that most of your money goes for shipping the contents rather than the box. And of course, the box is reusable. At one time this sort of thing was pretty common among homebuilders. Me and a few other fools still do it but the very idea of helping each other as we build our thousand dollar airplanes has fallen below the dollar-oriented radar of today's homebuilt community.
The ‘Experimental - Amateur Built' licensing category exists to promote EDUCATION. If you're willing to jump through U.S. Postal Service hoops you can even ship your parts back & forth at a special rate for Educational Materials.
Man really CAN fly... with a little help from his friends.
-R.S.Hoover
"What's it made out of?" I ast him. He didn't know, guessed it was steel. "What kind of steel?" I ast him. Blank stare.
I went out to the little shed, chased the possoms off the top shelf, found the CUBY file box, pulled it out. He'd followed me, stood at the door acting like he's never seen a possom before. Or a stack of blueprint filing cabinets. The Cuby plans weren't in the cabinet. Like most plans they have their own box. He helped me put the V77 box back on the shelf then followed me back to the shop.
Dingus was shown as steel, no alloy specified. It's not a very good drawing. (Drawing reference about 18-D) I flipped through the plans looking for a more detailed drawing but don't find one. Which doesn't mean it ain't there.
The dingus is properly called the ‘slide' and acts as the carrier for the AN4 bolt that is the travel-limiter on the Cub's gear. It goes inside the short strut, which is 3/4 x .058 so the OD of the dingus is called out as five-eighths, which should work. Drawing shows it as being just half an inch thick with a significant chamfer, which won't work, unless you've got some dimensions to go by. I point out the missing dimensions which makes the existing dimensions questionable. He waves a lot of money at me and I am wooed into making him a couple of dinguses (denguii?).
The guy quickly lost interest in watching me set up the lathe, started nosing around the shop, which I don't like. People steal things. Even nice people like fellow pilots, or rich people like most homebuilders. (Yeah, I know. Richer than me, though.) I sat him down in the patio and gave him the set of plans to play with while I made his dinguses.
I didn't have any five-eights rod but I had a stub of free-machining three-quarter stock so I used that, turned it down to .625. I made the dingus five-eights in length with a sixty-thou chamfer on each end. Drawing said the quarter inch hole was drilled, which would probably work in most cases, so I laid them out, set them up in a vise on the drill press, piloted them to something smaller then opened them up with a freshly sharpened quarter-inch bit. Broke the edges, buffed them up, tried them with an AN4... kinda tight but good enough for a Cuby.
He admired the shiny little slugs of steel then tucked them in his pocket and asked, "Did you make this?" flapping the lid of the plans-box back & forth like a punkah on the ceiling of a bungalow in Krishnapur.
A plans box is just a shallow plywood tray with a hinged plywood lid. The hinge on this one was a piece of leather salvaged from an old pair of boots. Of course you make them, for crysakes. I just looked at him. Okay, maybe I rolled my eyes or something.
"I've never seen anything like it," he said. Which told me he hadn't been on many construction sites. Or boatyards. Nor built many airplanes. After he left I put some moth crystals in the plans box and put it back in the shed and went back to what I was doing, which has banging a bulkhead out of some .020.
Plans usta be blueprints - blupes. Blupes fade so you store them in the dark. Most modern drawings don't fade but over the course of time needed to finish most homebuilts they tend to get torn, damaged, dirty or lost... unless you do something about it.
Real shops, you've got a filing cabinet for your drawings. And that is one humongous cabinet. When I worked for Vernon Payne he had three of the things, about four by six feet on a side and three feet high with about a dozen drawers in each. Building just one airplane, and working from just one set of drawings, there's no way to justify the cost or space for a flat file cabinet. So you build a flat file BOX. Small box, you can hinge the lid. Big box, as in three by four feet, the lid usually attaches with latches.
What you build it out of depends on you and the night and music. Building a metal airplane? They you'd probably use aluminum. I've made one out of fiberglas but I was just showing off. Mostly, I make them out of wood.
Everybody does this. Don't they?
HOW TO MAKE A PLYWOOD PLANS-BOX
Start with a frame of one-by-two pine. Make the interior about one inch larger than your drawings in each dimension. Assemble the frame using glue and dowels or corner blocking. Don't use any nails; we're going to run it thru the saw later on.
Skin the box with 1/8" luan plywood. If you use staples or brads, pull them out after the glue cures.
Clean up the edges then run the box through the saw ON EDGE so as to cut the one-by-two. As soon as you cut one side, tack some plywood over the cut. Cut all four sides, being sure to keep the same face to the fence so the cut will come out even all around.
Clean up the cut line, clamp the box back together and install a piano hinge opposite which ever side you want it to open. Give it a seal coat of 50-50 varnish:thinner, let that cure for a couple of days then give it a light sanding, wipe down with thinner and lay on a full coat of varnish. If you remembered to varnish under the hinge the thing will be good for about fifty years, give or take a decade or so.
That's the DeLux model. I've got a couple like that but most are more along the lines of a Jeep than a Cadillac. The frame is often pieced out from scraps of 3/4" square stock or whatever happened to be available when I needed to make a plans box. Some use cardboard for the skins instead of plywood, which works okay if you add a few stiffeners and give the cardboard a couple of coats of oil-based paint.
It helps if you start with a frame that is square so use corner clamps if you've got them. But close enough is good enough in this case. Lots of times I use scrap to make up a pair of open trays rather than a box. When I get around to it I clamp them together, true up their edges by running them through the bandsaw then do a few passes against the disk sander. That gives the box a uniform outside appearance and a nice neat edge. Inside, the thing may be crooked as hell but the plans don't know the difference.
The types of hinges I've used range from real hinges, including some aircraft stuff, to anything that has enough flexibility, such as leather or upholstery material. Fabric or leather hinge, you can glue it on if you remember to cover the parting line with tape so as not to glue the box together. If you use brads or screws make sure you have enough depth of wood to provide the support required. Flat belting used to be the first choice for this sort of hinge but you don't see it around much any more.
If you want to make it air tight, run a bead of RTV along the closing line, cover it with waxed paper and leave it closed until the RTV has cured. Then clean things up with a razor. If it's a DeLux version, such as a gun case or whatever, you can route the edge to accept a strand of O-ring stock.
The latch is usually a couple of round head brass brads and a piece of safety wire but anything that does the job is acceptable.
WORKING WITH WOOD
Discovering that every aircraft mechanic needs to be a pretty good woodworker always comes as a bit of a shock to guys wanting to build an airplane out of plastic or metal or steel tubing. If you want to build an airplane - ANY AIRPLANE - and have no experience working with wood, it might be a good idea to get some. Making a box for your plans isn't a bad way to start.
Nowadays, spend a thousand dollars for a good tool, it's liable to arrive in plastic bag. Making small boxes of every conceivable size, shape and strength is a recurring chore for anyone who has a few machine tools because if you just throw stuff in a drawer the odds are it won't be usable when you need it.
THE BEAUTY OF BOXES
Airplanes aren't very heavy. (You wish!) Whole wing's-worth of ribs, metal or wood, only weighs a couple pounds. But bulky and fragile pounds.
Odds are, someone is building the same airframe as you. A good building strategy is to become a part of a group working on the same design. If you can come up with a safe, inexpensive method of shipping stuff back & forth, having one guy do the wing ribs while another does the tail and a third does this and the fourth does that... often saves a lot of time in producing the components.
Parcel Post offers dirt cheap shipping for a container of a given size and weight. Not fast, just cheap. A sturdy plywood shipping container made of pine stringers and eighth-inch plywood is strong enough to protect fragile components yet light enough so that most of your money goes for shipping the contents rather than the box. And of course, the box is reusable. At one time this sort of thing was pretty common among homebuilders. Me and a few other fools still do it but the very idea of helping each other as we build our thousand dollar airplanes has fallen below the dollar-oriented radar of today's homebuilt community.
The ‘Experimental - Amateur Built' licensing category exists to promote EDUCATION. If you're willing to jump through U.S. Postal Service hoops you can even ship your parts back & forth at a special rate for Educational Materials.
Man really CAN fly... with a little help from his friends.
-R.S.Hoover
AV - How to Make Ribs Out of Old Orange Crates
.
A fellow who has been following my posts about building airplanes on the cheap wrote to say he'd found plenty of straight grained hemlock 2x4's at his local Home Depot. Then he said he couldn't use it because it was full of knots. I smiled at that, fired off a message telling him not to worry about the knots. The knots would vanish as the work progressed. That got me a rather grumpy reply about wasting his time.
Apparently the fellow doesn't believe in magic :-)
Magic has been defined as anything we don't understand. At one time the ability to do long division or work with fractions was considered magical. Making knots vanish is no more difficult than long division.
STICK RIBS
Have you ever made one? Probably not. Which is kinda sad because stick ribs are a key factor in building a strong, light-weight, efficient and inexpensive wing. Once you know how to build a good wing the rest of the airframe is relatively easy.
To give you some idea as to what I'm talking about I've provided a couple of photos of stick rib construction and a drawing of the airfoil. Mr. Ryan Young, the Coast Guard's answer to Samuel Pepeys, has allowed me to pin the illustrations on his electronic wall.
(See: http://users.lmi.net/~ryoung/Sonerai/How_to_Build_Wing_Ribs.htm )
Making ribs is a fundamental Rite of Passage for homebuilders, each of whom has their preferred method. Some argue for fitting each individual stick, others for leaving them square; some insist on clamps versus fasteners, other feel the only practical fastener is a Monel staple; some use circular gussets, others are polyform but most use some version of a triangle. And then comes the Glue Wars...
Oddly enough, the myriad differences in rib construction vanish along with the knots as soon as you get some daylight under the wheels. All of that tiresome but socially-required Homebuilder Bullshit boils down to the basic questions of strength, weight, cost and convenience. Build your ribs in whatever way best matches your situation. So long as they are light enough and strong enough, the airplane will fly just fine. (As a basis for comparison the rib shown in the photos takes about fifteen minutes to assemble using 1/4" aircraft nails, weighs about 3.5 ounces and costs about fifty cents, all tolled.)
MAKING STICK RIB STOCK & VANISHING KNOT HOLES*
The longest pieces of wood in a stick rib are the cap strips - the top and bottom pieces. For a big, old fashioned airfoil the cap strips are liable to be five feet long. The other sticks in the rib, the verticals and diagonals, are shorter; maybe a foot long, max, with the others being even shorter than that. On a modern airfoil, say a 4415 having a chord of 48" and built with a D-cell leading edge, the cap strips are about three feet long and the longest diagonal is maybe nine inches, something like that.
The above is worth mentioning because it will help you understand why the knots drop out of the equation.
To turn a two-by-four into rib stock you set up the saw for whatever thickness you want then rip the two-by into laths. Ignore the knots, just cut right through them. If the lath breaks at a knot, don't worry about it. Once all the two-by-fours have been ripped into laths, run them back through the saw to produce rib stock. If you want square stock you don't even have to reset the saw.
When using locally available lumber the wiser course is to give yourself plenty of extra wood to work with. I generally cut about twice as much as needed, selecting the very best of the bunch for ribs.
When ripping the laths into rib stock you will again cut right through the knots. And again, some of the pieces will break at that point. No big deal.
After you've reduced your two-by-fours to rib stock you'll have a huge pile of sticks. Some will be full length, others will be shorter, having broken at a knot. Don't worry about it. We'll use the long pieces for our long sticks, short pieces for short sticks, discarding any knots we encounter along the way.
Now comes the grading. You're looking for clear, knot-free pieces having flat grain with a run-out of at least one-in-fifteen and long enough to serve as cap strips. Put the pieces on your work bench and examine the grain. Looking down at the piece, the grain should be looking up at you. If you can't see it, roll the piece over to expose the other edge. If the grain is not clearly visible on one edge or the other, discard the piece.
It isn't uncommon to find grain of sixteen to twenty in a two-by-four of Western Hemlock. The more gain, the higher the density and the heavier the piece so don't go overboard here. I'm happy with two to four annual rings across a quarter-inch rib stick.
Although grain run-out is a critical factor in the strength of the wood, any run-out greater than the length of that particular piece is acceptable. For example, on a diagonal that is nine and a half inches long you should be able to follow the grain for the length of the piece. That means almost any stick will meet the specs for the shorter members in a rib. The reason why this is so has to do with the manner in which wood carries a load and may be confirmed by a few simple experiments.
Once you've selected the pick of the litter for your cap strips, you're home free; the rest of the job is a no-brainer. Cut your cap strips to length and bundle them using rubber bands. Use the residue to make up the vertical and diagonal pieces.
WORKING WITH WOOD
I haven't bothered to mention the need for finger-boards (some call them ‘feather-boards'), pusher-sticks, hold-downs and a zero-clearance shoe. I consider this sort of thing to come under basic woodworking skills and have assumed anyone building a wooden wing or fuselage would be familiar with them.
Fabricating ribs, stringers, longerons and spar caps from locally available materials assumes the as-sawn rib stock will have a reasonably smooth surface and be of the required size. If you don't have a good saw or if you aren't a good sawyer, it might be wise to enlist the aid of someone with better equipment or more experience.
Some folks, mostly those who have never built anything, will argue that all of the wood in an airplane should be milled to size and free of splices. Wood that has been planed smooth certainly presents a more attractive appearance and I strongly recommend it for furniture. But as-sawn stock works perfectly well for ribs. In fact, if you order rib stock from a spruce supplier it will arrive in planks of the required thickness (i.e., one-quarter, five-sixteenths, etc) which you are then expected to rip to the required width.
Of course, if you're a skilled woodworker with a shop full of tools that includes a surface planer (not a joiner), and if you can afford the additional wastage, then you would probably mill all the stock you need to the required size. But many simply can not afford either the tools nor the wastage. Accurately sawn, with an eighth-inch kerf, about 60% of the material will end up on the floor as sawdust. Even allowing for the smallest possible clean-up cut in the surface planer will raise the wastage to about 75%
As for splicing, a scarf of twelve-to-one will typically equal the strength of the parent material and is often stronger. Just as we must splice short pieces of plywood in order to make long ones, when using locally available materials for our spars, caps and longerons, splicing is usually required not only to make up the required length but to eliminate any knots. All of the handbooks on the maintenance of wooden aircraft components contain examples of proper splicing procedures.
-R.S.Hoover
*Used in the theatrical sense, where to vanish something means to make it disappear.
A fellow who has been following my posts about building airplanes on the cheap wrote to say he'd found plenty of straight grained hemlock 2x4's at his local Home Depot. Then he said he couldn't use it because it was full of knots. I smiled at that, fired off a message telling him not to worry about the knots. The knots would vanish as the work progressed. That got me a rather grumpy reply about wasting his time.
Apparently the fellow doesn't believe in magic :-)
Magic has been defined as anything we don't understand. At one time the ability to do long division or work with fractions was considered magical. Making knots vanish is no more difficult than long division.
STICK RIBS
Have you ever made one? Probably not. Which is kinda sad because stick ribs are a key factor in building a strong, light-weight, efficient and inexpensive wing. Once you know how to build a good wing the rest of the airframe is relatively easy.
To give you some idea as to what I'm talking about I've provided a couple of photos of stick rib construction and a drawing of the airfoil. Mr. Ryan Young, the Coast Guard's answer to Samuel Pepeys, has allowed me to pin the illustrations on his electronic wall.
(See: http://users.lmi.net/~ryoung/Sonerai/How_to_Build_Wing_Ribs.htm )
Making ribs is a fundamental Rite of Passage for homebuilders, each of whom has their preferred method. Some argue for fitting each individual stick, others for leaving them square; some insist on clamps versus fasteners, other feel the only practical fastener is a Monel staple; some use circular gussets, others are polyform but most use some version of a triangle. And then comes the Glue Wars...
Oddly enough, the myriad differences in rib construction vanish along with the knots as soon as you get some daylight under the wheels. All of that tiresome but socially-required Homebuilder Bullshit boils down to the basic questions of strength, weight, cost and convenience. Build your ribs in whatever way best matches your situation. So long as they are light enough and strong enough, the airplane will fly just fine. (As a basis for comparison the rib shown in the photos takes about fifteen minutes to assemble using 1/4" aircraft nails, weighs about 3.5 ounces and costs about fifty cents, all tolled.)
MAKING STICK RIB STOCK & VANISHING KNOT HOLES*
The longest pieces of wood in a stick rib are the cap strips - the top and bottom pieces. For a big, old fashioned airfoil the cap strips are liable to be five feet long. The other sticks in the rib, the verticals and diagonals, are shorter; maybe a foot long, max, with the others being even shorter than that. On a modern airfoil, say a 4415 having a chord of 48" and built with a D-cell leading edge, the cap strips are about three feet long and the longest diagonal is maybe nine inches, something like that.
The above is worth mentioning because it will help you understand why the knots drop out of the equation.
To turn a two-by-four into rib stock you set up the saw for whatever thickness you want then rip the two-by into laths. Ignore the knots, just cut right through them. If the lath breaks at a knot, don't worry about it. Once all the two-by-fours have been ripped into laths, run them back through the saw to produce rib stock. If you want square stock you don't even have to reset the saw.
When using locally available lumber the wiser course is to give yourself plenty of extra wood to work with. I generally cut about twice as much as needed, selecting the very best of the bunch for ribs.
When ripping the laths into rib stock you will again cut right through the knots. And again, some of the pieces will break at that point. No big deal.
After you've reduced your two-by-fours to rib stock you'll have a huge pile of sticks. Some will be full length, others will be shorter, having broken at a knot. Don't worry about it. We'll use the long pieces for our long sticks, short pieces for short sticks, discarding any knots we encounter along the way.
Now comes the grading. You're looking for clear, knot-free pieces having flat grain with a run-out of at least one-in-fifteen and long enough to serve as cap strips. Put the pieces on your work bench and examine the grain. Looking down at the piece, the grain should be looking up at you. If you can't see it, roll the piece over to expose the other edge. If the grain is not clearly visible on one edge or the other, discard the piece.
It isn't uncommon to find grain of sixteen to twenty in a two-by-four of Western Hemlock. The more gain, the higher the density and the heavier the piece so don't go overboard here. I'm happy with two to four annual rings across a quarter-inch rib stick.
Although grain run-out is a critical factor in the strength of the wood, any run-out greater than the length of that particular piece is acceptable. For example, on a diagonal that is nine and a half inches long you should be able to follow the grain for the length of the piece. That means almost any stick will meet the specs for the shorter members in a rib. The reason why this is so has to do with the manner in which wood carries a load and may be confirmed by a few simple experiments.
Once you've selected the pick of the litter for your cap strips, you're home free; the rest of the job is a no-brainer. Cut your cap strips to length and bundle them using rubber bands. Use the residue to make up the vertical and diagonal pieces.
WORKING WITH WOOD
I haven't bothered to mention the need for finger-boards (some call them ‘feather-boards'), pusher-sticks, hold-downs and a zero-clearance shoe. I consider this sort of thing to come under basic woodworking skills and have assumed anyone building a wooden wing or fuselage would be familiar with them.
Fabricating ribs, stringers, longerons and spar caps from locally available materials assumes the as-sawn rib stock will have a reasonably smooth surface and be of the required size. If you don't have a good saw or if you aren't a good sawyer, it might be wise to enlist the aid of someone with better equipment or more experience.
Some folks, mostly those who have never built anything, will argue that all of the wood in an airplane should be milled to size and free of splices. Wood that has been planed smooth certainly presents a more attractive appearance and I strongly recommend it for furniture. But as-sawn stock works perfectly well for ribs. In fact, if you order rib stock from a spruce supplier it will arrive in planks of the required thickness (i.e., one-quarter, five-sixteenths, etc) which you are then expected to rip to the required width.
Of course, if you're a skilled woodworker with a shop full of tools that includes a surface planer (not a joiner), and if you can afford the additional wastage, then you would probably mill all the stock you need to the required size. But many simply can not afford either the tools nor the wastage. Accurately sawn, with an eighth-inch kerf, about 60% of the material will end up on the floor as sawdust. Even allowing for the smallest possible clean-up cut in the surface planer will raise the wastage to about 75%
As for splicing, a scarf of twelve-to-one will typically equal the strength of the parent material and is often stronger. Just as we must splice short pieces of plywood in order to make long ones, when using locally available materials for our spars, caps and longerons, splicing is usually required not only to make up the required length but to eliminate any knots. All of the handbooks on the maintenance of wooden aircraft components contain examples of proper splicing procedures.
-R.S.Hoover
*Used in the theatrical sense, where to vanish something means to make it disappear.
VW - Polished Crankcase II
Polished Crankcase
Don’t do it. Not if you intend to drive the vehicle. If it’s something for display, feel free to polish it to a nice shine. A coat of clear laquer will preserve the polish for about a year.
But if you intend to drive the vehicle, give the cleaned, deburred crankcase one final wash with hot soapy water followed by a boiling water rinse and allow it to air-dry. A touch of compressed air through the oil passages would be wise (and I assume all plugs are out).
Your clean, dry case should be protected with a thin coat of flat black paint on its exterior surfaces. Do not use a hi-temp paint as the high clay or eutectic metallic content that gives such paints their high-temperature qualities acts as a thermal insulator. What you want is a surface that will radiate heat. Polished surfaces reflect heat. If you polish your crankcase it will run considerably hotter than normal.
This isn’t an automotive hints & kinks sort of thing, it’s simple physics. Veedub drivers in cold climates have long known the benefit of chrome plated valve covers and push-rod tubes. The heat-reflective surfaces cause the engine to run from ten to thirty degrees hotter.
The original Volkswagen engines (1935-37) was designed for a service life of 100,000 km; it didn’t even have replaceable bearing shells. But through the use of full-flow oil filtration systems the service life of a properly assembled VW engine can exceed 300,000 km, which means the engine may be exposed to the elements for 20 years or more, and that justifies a protective coat of paint.
Flat black paint is virtually transparent to heat radiation. Giving your crankcase, push-rod tubes and valve covers a coat of flat black paint atop bare metal actually promotes engine cooling. One of the quickest ways to spot a professionally built engine is from its somber flat-and matte-black surfaces.
Don’t do it. Not if you intend to drive the vehicle. If it’s something for display, feel free to polish it to a nice shine. A coat of clear laquer will preserve the polish for about a year.
But if you intend to drive the vehicle, give the cleaned, deburred crankcase one final wash with hot soapy water followed by a boiling water rinse and allow it to air-dry. A touch of compressed air through the oil passages would be wise (and I assume all plugs are out).
Your clean, dry case should be protected with a thin coat of flat black paint on its exterior surfaces. Do not use a hi-temp paint as the high clay or eutectic metallic content that gives such paints their high-temperature qualities acts as a thermal insulator. What you want is a surface that will radiate heat. Polished surfaces reflect heat. If you polish your crankcase it will run considerably hotter than normal.
This isn’t an automotive hints & kinks sort of thing, it’s simple physics. Veedub drivers in cold climates have long known the benefit of chrome plated valve covers and push-rod tubes. The heat-reflective surfaces cause the engine to run from ten to thirty degrees hotter.
The original Volkswagen engines (1935-37) was designed for a service life of 100,000 km; it didn’t even have replaceable bearing shells. But through the use of full-flow oil filtration systems the service life of a properly assembled VW engine can exceed 300,000 km, which means the engine may be exposed to the elements for 20 years or more, and that justifies a protective coat of paint.
Flat black paint is virtually transparent to heat radiation. Giving your crankcase, push-rod tubes and valve covers a coat of flat black paint atop bare metal actually promotes engine cooling. One of the quickest ways to spot a professionally built engine is from its somber flat-and matte-black surfaces.
VW - Pulling Dowels
Pulling Dowels
(I’ve) tried everything but the last dowel refuses to come out.
The dowel may have picked up a bit of debris when it was installed, causing it to wedge. Heating it in an oven may help. Your torch provides only localized heat, it gets the surface too hot by the time the heat penetrates to the root of the dowel; heating in an oven allows the heat to soak in.
You can pull any dowel simply by grasping it with a collet-type puller and vibrating the crankshaft with an air-hammer. The usual method is to use to a blunt-nosed chisel in the air-hammer, inserted into the pulley retainer bolt’s thread bore so the blunt-nosed chisel rests against he bottom of the hole. The crankshaft is supported in a padded vise, the collet-puller is tightened onto the dowel pin and pulled firmly by hand as you rap the thing with the air-hammer.
No collet? Then use vise-grips. Dowels are hardened. You can’t mar a properly hardened dowel with vise-grips. Some guys don’t even bother with a collet (i.e., a gripper that grasps the full circumference of a shaft. VW dowels come in three diameters. You’ll need a different collet for each size.). Instead, they take a pair of cheap vise-grips with soft jaws and drill them for the size of dowel they want to grip, less a few thou.
No air-hammer? Then use a regular hammer. Just be sure not to damage the crankshaft by hammering on it. No heavy blows. Pretend you’re an air-hammer.
Why does it work?
I don’t know. Different mass-ratios or something. But it does work . . . all mechanics and machine shops pull dowels this way. Or maybe not all, seeing the trouble your local shop had with it. I’d better make this a public post.
If sleeve retainer was used to secure the dowel-pins you’ll need to heat the crankshaft to at least 450 degrees. Do this in an oven, where you can control the temperature. Let it heat-soak at least an hour to be sure the heat has penetrated to the dowels. After getting out the dowels, put the crank back in the oven, bring it back up to 450 degrees, let it heat-soak about an hour, then shut the oven off and leave the crank in the oven 24 hours or until the thing is stone cold.
(Revision Note: Despite a number of messages from ‘professional’ mechanics saying they’d never heard of a ‘dowel puller,’ such tools are in fact commonly available and every engine overhaul shop usually has one. They are available from Proto, Snap-On and most other suppliers to the trade. The dowel puller usually consists of a number of collets in SAE and metric sizes, which screw into a slide-hammer. When the slide hammer can’t win the dowel free, the trick with the air-hammer is used.)
(I’ve) tried everything but the last dowel refuses to come out.
The dowel may have picked up a bit of debris when it was installed, causing it to wedge. Heating it in an oven may help. Your torch provides only localized heat, it gets the surface too hot by the time the heat penetrates to the root of the dowel; heating in an oven allows the heat to soak in.
You can pull any dowel simply by grasping it with a collet-type puller and vibrating the crankshaft with an air-hammer. The usual method is to use to a blunt-nosed chisel in the air-hammer, inserted into the pulley retainer bolt’s thread bore so the blunt-nosed chisel rests against he bottom of the hole. The crankshaft is supported in a padded vise, the collet-puller is tightened onto the dowel pin and pulled firmly by hand as you rap the thing with the air-hammer.
No collet? Then use vise-grips. Dowels are hardened. You can’t mar a properly hardened dowel with vise-grips. Some guys don’t even bother with a collet (i.e., a gripper that grasps the full circumference of a shaft. VW dowels come in three diameters. You’ll need a different collet for each size.). Instead, they take a pair of cheap vise-grips with soft jaws and drill them for the size of dowel they want to grip, less a few thou.
No air-hammer? Then use a regular hammer. Just be sure not to damage the crankshaft by hammering on it. No heavy blows. Pretend you’re an air-hammer.
Why does it work?
I don’t know. Different mass-ratios or something. But it does work . . . all mechanics and machine shops pull dowels this way. Or maybe not all, seeing the trouble your local shop had with it. I’d better make this a public post.
If sleeve retainer was used to secure the dowel-pins you’ll need to heat the crankshaft to at least 450 degrees. Do this in an oven, where you can control the temperature. Let it heat-soak at least an hour to be sure the heat has penetrated to the dowels. After getting out the dowels, put the crank back in the oven, bring it back up to 450 degrees, let it heat-soak about an hour, then shut the oven off and leave the crank in the oven 24 hours or until the thing is stone cold.
(Revision Note: Despite a number of messages from ‘professional’ mechanics saying they’d never heard of a ‘dowel puller,’ such tools are in fact commonly available and every engine overhaul shop usually has one. They are available from Proto, Snap-On and most other suppliers to the trade. The dowel puller usually consists of a number of collets in SAE and metric sizes, which screw into a slide-hammer. When the slide hammer can’t win the dowel free, the trick with the air-hammer is used.)
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