Re: 0.502" Drill bit?
 

Question.....What material is the shaft? If it's aluminum, it will tend to be barely just too big. Steel .5" shaft fits perfectly though....at least that's my experience. I got a flywheel machined and tried to put it on a .5" aluminum shaft and it barely wouldn't fit. So I took it to home depot to try and find another aluminum shaft that might fit (different batch, right?). All of them gave the same result. So I tried the steel shaft, and it fit perfectly.

Re: 0.502" Drill bit?
 

The two shafts are made with different tolerances.

Standard 0.5" aluminum extruded round will be somewhere in the range of +-0.005" on the diameter. It's never going to be 0.500" even. You would need precision ground shaft. Even with precision ground shaft, you could have anything from 0.500" to 0.4998" (for example, using McMaster standards). If it's 0.500" even, it's not going to go into a 0.500" hole.

The tolerance on steel round stock is generally +0 and minus a few thousandths, leading to your shaft fitting nicely into a 0.500" hole.

Re: 0.502" Drill bit?
 

Team 975 once had to hone out a pair of 5/8" bore flanged steel sprockets to fit a 16 mm shaft. I figure it was probably .004" or so. We used a 5/8" shaft in a drill press and a lot of valve grinding compound. It took a lot of time but the fit was beautiful. Next time that was needed, we just spun the shafts and sanded them down to fit. Much easier. :D