Quote Originally Posted by cwilliamrose View Post
A piece of plywood (or similar) with a radius cut on one edge with a bandsaw, then clamped to a sturdy table.
Hi Bill - This a great idea - I'm really glad I thought of it .

So, some comments on how to go about doing this:
1. IMHO the plywood mold should be made with the curve extrapolated at each end by a few cm/inches - this should be done because otherwise your bent tube will have short straight segments at each end. Of course you may be able to get away with no extrapolation of the curve if you cut the tube to be a few cm/inches longer at each end, and insert a straight bar into the extended ends.
2. Generate the curve representing the centerline of the tube in SW while taking into account that it should be a planar 2D curve. (It may be oriented in 3D, but remember that the mold/plywood is 2D). You can generate the curve using any combination of circular arcs, ellipses, conic sections, and splines.
3. Offset the curve by half the diameter of the tube.
4. Make a SW drawing of the offset curve and export it (File>Save As>*.DXF). Include a calibration line of known length in both X and Y axes.
5. Take the DXF file to your local print shop and have it printed at a 1:1 scale. Measure the actual length of the calibration lines before proceeding.
6. Stick the print to your plywood sheet using a non water based glue. (Paper expands when wet).
7. Do your stuff with the bandsaw.
8. You now have the tooling for mass production of your airframe.