cutter wrote:
Slow and steady progress. I did not use a fixture, looks straight to me.
Next a couple more formers, bending wire and then the stringers.
Adam
There is a reason that the fuselage of a properly laid out laser cut kit, using half former construction, will build straighter than a die cut kit.
Dies are expensive, and subject to tolerances, so when you lay out the parts for a die cut kit, you do half the formers on a sheet of wood. This reduces the cost of making the die and, because there is only one half former die for each former, assures that each half former is the same size as it's opposite half. The disadvantage is that each half former is cut from a different sheet of wood and there is almost no way that each sheet of wood will have the same density, stiffness and response to moisture in the air. Thus you usually must use a fixture when building to eliminate "banana fuselage".
With laser cutting there is no physical die, and each image of the former half is the same size, even if reversed, so the proper thing to do is lay out both halves of the formers on the same sheet of wood. This eliminates the built in propensity to warp. Some may argue that a single sheet of balsa can vary in density and stiffness from one end to the other but a proper laser cut layout puts both halves of a former pair next to each other, interleaved if possible, so that each half former is cut from approximately the same piece of real estate on the balsa sheet. If you have a dead flat building board and you are careful to get the former halves perpendicular to the vertical keel, a laser cut kit will build straight.
Howard
