Drilling wood spars for fittings

A simple little jig for drilling wood spars for fitting. Weld the "U" shaped jig up from scrap metal, weld the tube to the jig in one piece, stress relieve, cut center of tube out. For tube use 4130 X .058 wall. For example, for 1/4 dia bolt holes, use a piece of 4130, 5/16" dia x .058 wall thickness for a 1/4" dia drill bit. For 5/16" bolt use 3/8" dia X .058 tube.
Put a drill bit in backwards on the back side to aline the jig and then drill from the other side.
Dan
3/16" drill use= 1/4"x .058 4130 tube
Added --- 1/4" drill use = 5/16"x .058 4130 tube
5/16" drill use = 3/8"x .058 4130 tube

The jig in the picture was made when I was building my KR-2 in 1975 and still using it when I was building the wings for the little single seat Super Cub that I am flying now.