[Jon Stratis]

From your suggestions, my team had actually tried to mill down a 1/2" hex shaft to a square to fit. We had a nice interference fit, but the issue really is the amount of material you end up removing. The result is a very small shaft that, in our case, ended up sheering under load (the motor never stalled, we got about 10 turns before it broke). So, the lesson there is don't use aluminum shaft if you go that route!