I probably made this more difficult than it needed to be. As noted in a previous entry i pinned the left and right main wing spars to the center section spar with 23/64 steel pins. Measured the dihedral of both spars at 3.6 degrees. The dihedral is not specified in the plans but I wanted to ensure left and right were the same and that I had a reference point to monitor while drilling to the final size making sure nothing moved.

Next I clamped the top and bottom area where I would be drilling using a couple of deep reach clamps and small blocks of wood with over sized holes (for the pins to fit through) for protection of the metal front and back. The purpose of the clamp was to keep all the layers of metal together while I drilled and reamed the middle holes.

I started the process with the middle hole top and bottom on each spar. First I used a letter U drill (.3680") to enlarge the hole from the original .3595". Then I reamed to the final size using a .3745 reamer. The plans call for a .3750 reamer but I did some test runs on a scrap block of aluminum and found the .3745 gave the best snug fit for the close tolerance bolts. I installed a 3/8 bolt and castle nut to hold everything in place and removed the clamps. I verified the dihedral stayed at 3.6 degrees on each spar as I drilled and reamed each hole. All 12 holes were drilled, reamed and bolts temporarily installed.

All the close tolerance bolts fit nice and snug.