Creation of jig for positioning wing ribs 2, 3 and 4

A few months ago, it was discovered that tolerances in the main spar rib attachment brackets were sufficient to make skin fitting very difficult, if the ribs were simply rivetted in place "Dealing with slight misalignments between the ribs and main spar mounting brackets". In one case (left rib 3) the error was so great that the rib tail would be rotated 10 degrees up from the correct position. In many other cases a 0.7-1mm front-back mismatch would be present between the skin and the rib-flange holes, making clecoing impossible without excess forcing of the skin, or otherwise requiring hole "cleaning" (quite the wrong move, better to tackle the underlying cause)

The decision was taken to upsize the holes in these attachment brackets, to 4.8mm so as to absorb these errors. The top and bottom-most holes were left at 4mm and the rib holes were elongated enough to permit the rivet to pass though. TAF indicated this was the factory practice to absorb any small errors, for all of the holes. TAF ok'ed with my proposal to upsize the middle holes to 4.8mm in what they agreed would be an even more sound remedy. The fact that elongation is acceptable in practise was of some reassurance as I would not be able to upsize all holes. The top and bottom-most 4mm holes are too close to the edge of the brackets for an upsizing to be acceptable, from the 2-D rule. TAF agreed on this point.

But it is necessary to hole the ribs exactly in position as if the skins were in place. Using the real skins would be very inconvenient and risky, and would limit access. So I made small skin sections matched drilled to the actual skins, as follows. By flipping, the jigs are good for both left and right wings. The need to man-handle the wings to mount and unmount the skins is avoided.