Vet Thomas is a fellow EAA Chapter 44 member and a professional machinist. I spent an hour in his shop and he demoed drilling a "tight fit" 1/4" hole in 1" x 1 1/4" aluminum block, such as in the W11-04 Wing Attach Blocks:
* AN aircraft bolts are typically about .003" undersized to start with. * For a 1/4" hole, set the drill press on the slowest speed. * Start with a drill bit that's a few thousanths (or even 1/32") undersized. Don't start with a very small pilot bit as I did - it just clogs up) * Use lots of lubricant while drilling (he uses WD-40) * Clamp the piece in a drill press vice. He didn't clamp the vice to the table in this instance. * Use modest pressure to keep the drill moving steadily while drilling. * For the final size bit, clamp it only 1/4" or so up into the chuck so that it can track the pilot hole. * Use plenty of lubricant and light pressure.
Instead of a reamer, I found slightly undersized bits at Ace Hardware and drilled the final holes at 1/4". It was successful and the holes are definitely snug. Bolts no longer drop iin, but require a gentle push.
