Tuesday, November 21, 2006

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?


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.


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.


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.


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