Ted Ernst gave lot of good advice, but one bit is, I believe,
controversial:
> [When hammering] you must support the crank so you don't pit the
> races or crack your balls.
My quibble is with the word "must".
Now I'm not saying you can't possibly pit the races or crack the balls, but I can tell you that in my time as a bike mechanic, I hammered in many cotters without supporting the crank, and never caused any damage that I could detect. Nor have I ever seen any such damage caused by other mechanics' hammering. I'd say the likelihood of such damage is extremely low, for normal mortals wielding the hammer anyway. (Ted is stronger than most!)
I'll agree that supporting the back side of the crank for hammering is a good idea, especially for an extra-hard-to-remove pin. (You get more bang per bang, since the impact isn't dissipated in flexing the various parts of the bike, bike stand etc.) I'm just usually too lazy to bother.
My own townie bike has had the cranks off and back on numerous times over the last almost-40 years, sometimes using a VAR pin press, but plenty enough times they were just hammered off and on. Lots of miles on it and I'm a big guy, yet the bearing is quite smooth. If I was damaging it I would know by now.
BTW, my favorite punch for hammering (before I got my VAR press) used to be another cottered BB axle, that had a dimple in the end that matched the rounded end of the cotter. A pitted trashed axle of course, I wouldn't do that to a good one. Not the world's best drift punch maybe, but the divot did hold the punch centered on the pin nicely, and prevented damage to the ends of the pin. In my experience BB axles are tough enough not to shatter when struck with a hammer, but of course you should wear eye protection and YAMV ("your axle may vary").
Mark Bulgier
Seattle WA USA