I started by back-drilling the doubler plates at each end of the aileron spars, then drilling the aileron hinges up to size for bolts. The holes start out at #30 (1/8″). I used a core drill (similar to a reamer) to take the holes from .128 to .189. That is the decimal size of a #12 drill, which is what the plans call for. I like using core drills and reamers because they create a nice clean hole.
The pictures show the inboard and outboard hinges.
The next step is to fully assemble the ailerons with the aft skin and the leading edge skin, the nose ribs, the main ribs and the counterbalance, which is just a length of galvanized pipe. The holes are all taken up to their proper hole sizes. Most of the holes are #40, but the bottom fasteners attaching the skins to the spar will be pop-rivets, since there is no access to use solids to close the aileron. Those holes get taken up to #30.
You have to leave a little bit of space to get the counterbalance pipe through, then it gets clecoed closed.
The counterbalance pipe just nestles in the leading edge curve of the nose skin, and is secured with pop rivets along the length and in the nose ribs on the ends. Here’s a picture of the pipe in the leading edge:
To drill the holes in the pipe, I used BoeLube to lubricate the drill bit. I started with a #40. The key when drilling steel is slow speed and high pressure on the drill. Otherwise you’ll smoke the drill bit and go through a few of them in the process.
The holes then get taken up to #30. You can see how the pipe is held in by the nose rib.
The fastener holes through the nose rib also have to be drilled. To do this, you remove the aft skin, and use a long #30 drill bit to go through the spar and rib assembly into the hole in the rib for the counterbalance pipe. I also used BoeLube here.
After everything is taken apart, the counterbalance holes get countersunk to allow for the dimples in the skin. Accuracy of the countersink is not important, because the skin and the rivet will conform.