I mated the spars. I decided to up-drill the wing attach blocks up to their final size of 3/8" while I had the spars on my workbench. I accomplished this by first removing the attach blocks from one spar and step drilling those using my milling machine until they were close to the correct size. I then reamed the holes to match the AN-6 bolts I have to attach the wings to the fuselage. These attach blocks will assist as a drill guide when I drill through to the other attach block on the other spar.
To help in keeping the holes lined up between the attach blocks on the different spars, I used a series of concentric brass tubes which acted like very finely adjustable drill bushings. I purchased a set of K&S round brass telescoping tubing. These brass tubes precisely fit inside of each other and come in various 1/32" increments. Using these tubes stacked together in the attach block holes that were previously up-drilled to the proper size, I was able to carefully drill though the spars to the remaining attach blocks and get them up-drilled in increments of 1/32" until just below the final size. I then finished the holes with the reamer.
This process worked fairly well but took some time to complete. The upside is that the holes are precisely aligned and will make wing rigging go more smoothly.
Drills, brass tubing, and reamer used to mate the spars.
Concentric brass tubes in attach block guide hole, which act as mini drill bushings.
