Precisely reaming plastic
OP speaking. Quick version: What should I bear in mind when attempting to ream out a slightly greater internal diameter of a plastic bushing?
Blow-by-blow version: Wiggle-wiggle-wiggle worked: the right/outer arm (the troublesome one) of my Mafac "Racer" came off; and then the left/inner arm (easily) came off too. Nothing looked odd about the right boss. The red plastic bushing that goes on it looked as if it was very slightly dirty, or perhaps just stained: I cleaned it up but this didn't bring any improvement in pivoting. I guessed that either the boss was too big or the internal diameter of the bushing was too small. So I tried each arm, back to front, on the "wrong" boss. (Of course the brake shoe pointed outwards, but all I wanted to check was the ease of pivoting.) The left arm pivoted easily on the right boss; the right arm didn't pivot at all easily on the left boss. I infer that the right boss is OK but the bushing of the right arm is too tight. So I'd like to increase its internal diameter very slightly. My limited understanding of Wikipedia articles on related matters suggests that I should use a burr mounted on a milling machine, but I'm just a regular ignoramus with a cheap set of hand files. (I don't even have a vise.) I could just go ahead and try; but I wonder if there's any advice I might benefit from.