- All done with a razor blade
- Building both sides at once
- Matched sticks taped together
Collected by Michael J. Heinrich
Here's a procedure for making box frames that Tony Peters showed me when I was just starting out in this hobby. I think it's the easiest and most accurate way I know, and requires no fancy tooling at all. As with any technique in this tradition, I've added a bit here and there, and I also will bring in comments and tips from friends who've added to the craft. To these, named below in bold type, I send thanks for your thoughts and for good times around the Virtual Building Board of SFA.
Anyone doing this modeling for the first time should be aware of a great overview to building and flying F/F models: the best basic text for learning this stuff is a series Bill Warner did in Model Builder magazine, titled "Hey Kid!--Ya wanna Build a Model Airplane??" This series started with the basics of flight and learning how to "see" what a model is doing and how to deal with it, and works you through progressively more complex models and construction procedures that get you ready for anything you might want to try from there. It's a great source. Dennis Norman sells a ring bound reprint, by permission, of the entire series. Write him for details.
In this first picture below (ALL of them are bad, I'm sorry! I'm a builder, not an artist) you see several things: First and shiniest, the one tool I need to do all my chopping, scarfing, fitting and trimming: one single-edge razor blade, unadorned. You can chop straight through just about all you need with this, with a bit of practice, and save your ExActo blades for later. You learn quickly to cut vertically through your stick (or pair of sticks, as you'll see) by leaning the blade just barely into the cut, so the knife-edge bevel doesn't push outward against the wood. Also, pushing the razor sideways in a short slicing motion is way better and easier than straight down. Practice a little on bare sticks first; you pick up the skills fast.
LARRY MARSHALL: "So many modelers believe that a #11 blade can substitute for any other cutting device. As you've indicated, when building with sticks, you NEED single-edged blades, which don't crush the stick ends and can facilitate obtaining square cuts. They are NOT optional or some affectation of us old guys building model airplanes." To expand on Larry's comment: a nice #11 blade looks sharp, pointy, and efficient, but you need a long flat surface to sight down when cutting square. Save your #11 for slicing curves in sheet, and even then, leave stock for sanding.
The second thing I want to mention: I'm doing both left and right sides of the box here at one time, with no Saran wrap, no worry about gluing together, no nothing. Why? Because it's half the time that way, and more importantly, it's lots more accurate. I start by pinning the pair of top longerons to the line with side-by-side pins holding the longerons snugly. Then, I'll cut pairs of uprights, a little long, and glue them wherever they go. I'll put the bottom longeron in later, and you'll see why then. All the bits of wood that go against the top longeron--the uprights, any gussets like you see here at the sternpost, the scarffed piece that will form the stabilizer slot--all are glued in now, while I have room to work. You see the pin at the bottom of the too-long uprights, pushing them against the longeron for the glue to dry. This takes maybe fifteen minutes in aliphatic glue, less with Duco; so you'll go from one end of the fuselage to the other in that time, then go back and remove the pins for the next step.
--But not yet, there's one more thing I want you to look at here: I'm holding sticks taped together--it's part of how I make sure the wood I want is all matched up. See, store-bought sawn strips (which I use, because I'm lazy) are never quite perfect in dimension, and they're all different stiffness and weight. I use a gram scale to grade all the strips I have, then decide if the lightest ones will be stiff enough by bending them in both directions, selecting the stiffest (You'll notice those with straight, long grain are stiffer than ones where you see diagonal grain running through the stick on one side). Now, those stiff long ones are paired up for longerons, and the less-stiff ones can be used for the short bits (within limits: no punky wood, anywhere. You decide.). The taped-together part is so I can work with TWO bits of upright at a time, without having to fumble with them.
Here's the sternpost after the pins are removed. Everything hangs down well past the inner edge of the bottom longeron, and you see the little gusset bits glued to the upright, also long: so that when I trim the bottom line, that joint will be perfect and I won't have to fiddle with tiny angle bits, which sometimes can be a tricky angle indeed.
Now here's the bottom longeron in place. See where the diagonal braces (which can be even lighter wood, as they're all compression, and anything that will break them is more than the model will like anyway!) have been fit a little long, and they have been trimmed too when the cut was made; now they form part of the glue joint as well. The corners against the top longeron and uprights were beveled too, but I had room to work then, remember?
Joints are critical. The closer we get our sticks to fit, the better the airframe will be. Filling glue between balsa does not give a great joint. It's one reason I like cutting and trimming the sticks I use in the ways I do, it gets me joints that line up & fit in a pretty easy way. Also, I can spread out the joint over a longer area, when I cut my diagonals and uprights in one pass like you've seen here; if I had to make that four-bevel cut on each diagonal and get the lengths right before dropping it in, I'd go crazy.
The best thing to me about doing things this way is that I can't cut anything too short, ever. There's no fiddling around trying to fit exactly between top & bottom longerons, or do any of the other fiddly bits need anything fancy at all.
With a frame like I'm making here, there's not so much stress to that gentle curve of the bottom longeron, and the diagonal braces will keep the curvy part from moving when it's freed up. But you do want to consider those stresses, and in your own box frames you may add a brace or two in areas you might be worried about. Don't be afraid to depart from the draftsman's drawing, that's how you come to find your own way of doing things.
With stressed structures, a lot of us will give the frame a soak of water (usually mixed with ammonia, or Windex, to cut down the surface tension of the water and get it to seep in better), to relax the wood a little. Ammonia will loosen white-glue or aliphatic joints, while Windex doesn't so quickly. Acetate- nitrate glues like Duco or Ambroid won't be affected.
Suggested by ART HOLTZMAN: "Many frames have pronounced curves at the chin, like from the nose block to the landing gear. When I encounter these, I carefully slice the longeron in half (1/16 sq into two 1/32x1/16) from the LG forward, wet-form the curve on a mold, and run some glue down the split to bond it together again. Once dry, lay it on the plan and keep on building."
I'll let this dry overnight then I'll take out the pins and sand the top of the double frame while it's still sticking to the wax paper, just a gentle sanding to bring down any high spots.
Speaking of wax paper, another neat trick comes from DAVE MITCHELL: tack everything to your board using Artists' Spray Mount repositionable adhesive, available in rattlecans at art and craft outlets. Put the plan down to the board with it, stick wax paper over that, and you'll have a smooth flat surface that doesn't bunch or wrinkle under your work. Better yet, this sanding procedure can be done with incredible ease when all's tacked down and the frame is hanging to the wax paper.
