I’ve been making foam wing cores for years, but the real hideous terrifying task related to that has been making the templates. I have always felt that if I’m going to make a core from a set of airfoil coordinates I should reproduce the curve described by that set of coordinates, or I’m making something else.

Well, folks, I think I’ve found the magic.

I use Compufoil to produce the template patterns. Compufoil generates two templates per rib: a top surface and a bottom surface. At least some of the bottom surface is generally concave. The daunting and finicky task, for me, has always been sanding the concave surface to be very smooth, and still follow the pattern line exactly

Tower Hobbies recently had (and may still have) the little Dremel Belt/Disk Sanders on sale. I bought one, and then tried a trick a machinist friend told me about for sanding sharply concave surfaces. With a knife make a small cut in the 1" wide belt in the “along-belt” direction about 1/4 " from the edge. Then tear the belt apart lengthwise starting at that cut. Reverse the tearing direction top to bottom about every 2 “. This prevents fraying of the belt by applying a little “rip-stop” action at each reversal I use 320 grit belts.

Now remove the Platen Part no. 30 from the sander. Put the 1/4” belt back on the sander. You can sand a gorgeous, soft edge on your phenolic or Formica pattern following the pattern line exactly, by gently feeding the pattern up against the belt, which will follow the pattern curve either concave or convex.

A little 0000 steel wool along the edge and you’re done.

Why do I find these things out so late in life?