I've got what appears to be a very low use Pratt Burnerd 8" 4 jaw chuck. The body is pristine with only some patina from hand prints. The L00 taper is very nice and clean (unlike many that get chip scars). And the jaws look almost new, though they do have a scar from what appears to be a carbide index tool the put a small diameter groove in the "inside" jaws. So, point being, it's not new, but it's not thrashed by any stretch.
I bought it at an auction for a very good price. But no chuck keys around, so I just looked at it's condition and "wiggled" the jaws. "Man, nice and snug, no wiggle at all, must be all but brand new." I say to my self. Bid went low, and I got it.
Fastforward to home that evening, examining my prizes.
Took my chuck key (didn't get one at the auction, box of keys in all sizes went for twice what the chucks did <shaking head>) and tried it out. MAN those jaws are stiff, but appear clean, what's up? And then it happened, turned the grub for jaw #1 and it turned REAL easy, but the jaw didn't move. Grub was broken at the thrust yoke. (sigh) And after clearing the thrust yoke, that jaw had to be driven out with a brass drift. Not wailing on it, but it sure didn't come easy. PB had a screw in stock and it is in transit, so still well worth the money.
Question is, why are the jaws so freaking tight? The appear to fit the screws just fine, but you can see it's rubbing HARD at the top of the jaw where the shoulders press against the face of the chuck. I blued up several jaws and the story is the same on them all, though #1 is the worst by a considerable margine. I used a stone to debur them and it helped, #4 is now fine, #2 and #3 are passable but slightly stiff over a small range, and #1 is still tight.
Makes me wonder if someone mixed up the jaws? How best to handle this? More stoning followed by Clover lapping compound? Should I be stoning the chuck or the jaws? I did try a tille light stoning on the jaws and the stone barely touched it.