More About Bearings and Lock Collars
Dec 12, 2013
I don't know why, but in recent years I've seen a rash of bearings with cracked inner races. Sometimes the damage was on relatively new machines with very few hours on them. Symptoms related to a cracked inner bearing race vary. Sometimes the bearing obviously failed in a dramatic and expensive way. Sometimes there was just an odd, once-per-revolution click or knock when the bearing/shaft was turned by hand. Either way, when the bearing was disassembled the inner race was cracked or broken in a half-moon shape. Sometimes that half moon-shaped segment stayed with the bearing after disassembly. Sometimes it came off with the lock collar.
And that was the clue to the cause of the problem in almost every case: the lock collar had been over-tightened. When the eccentric inside a lock collar "locks" onto the eccentric on the inner bearing race it can exert incredible force. If you've ever "started" a lock collar onto a bearing with just your fingers, then tried to slide the bearing and lock collar on the shaft, you were probably surprised by how little rotation it took to tightly anchor the bearing to the shaft.
It only takes a firm tap with hammer and punch or chisel to seat a lock collar onto a bearing. Pounding on a lock collar until it absolutely will not move another fraction of an inch is a great way to crack the eccentric edge of either the bearing race or the lock collar itself.
My personal strategy is to manually rotate the lock collar onto the bearing until I feel it "click" onto the bearing's inner race, then snug it finger tight. After that, a good, firm tap with a hammer and punch usually rotates the lock collar an additional 1/8 to 1/4 turn, and that's good enough.
Sometimes it's hard to walk away, when it's obvious I could give the lock collar another good smack and gain another few degrees of rotation, but in the case of lock collars and bearings, more is not always better.