I went away for the weekend and came back to a pile of cotter emails, at this rate there'd be a need for a separate mailing list for them.
I've only ever owned bikes with cottered cranks and have often helped out friends with pins they can't get out. I regrease the BB every few months so have fitted a ton of pins over the years. I love cottered cranks, the only thing to wear is the pin so you can keep them going for years and years.
I know everyone so far has been talking about the 'perfect' pins to fit and the perfect way to do it but I just don't bother as I don't think it's really necessary. The pins are cheap and, don't forget, soft so will 'fit' after a bit of use. Get one set of each type to check which fit nice and snug (better too big than too small) so can get the right ones to start with, I've got old ones of each size (with mushroomed threads). Sheldon's pages on cotters cover it all (pin to drive direction etc) but there's not much to it just line up the first crank to the BB spindle by eye, drop in the cotter and as just get enough threads through to screw on the nut and do the same on the other side. Use the cranks to wriggle the pins in as snugly as you can by hand until there's no movement and then whack the pin in with a hammer (practice if your aim's not good, no one wants a ding in their frame) and tighten the nut. Ride it for about 10 miles and tighten the nut again if you feel any play whack the cotter in again and tighten it again. Doing this will make the correct angle in the pin, filing it's just pointless.
I used a press once but pins just never work as well if you reuse them and ride hard, nothing like a fresh set. Even if there is a fine art to fitting them after you've changed them a few times you'll be as slap-dash as I am.
Julius Naim, London UK