Due to the events of life, I haven't been on here in quite awhile......but it's the only place I know of where experience is the rule.
I have a 1920 Hendey lathe that I rebuilt some years back and it's served me very well. It has a 10" Chinese 3 jaw mounted, which has always been very accurate. Or at least it was. The chuck started exhibiting signs that it needed to be cleaned so I disassembled it, cleaned everything and reassembled it. Note that Quan Lee (or whoever) mis stamped the jaw numbers, but it was assembled so that all three jaws meet on center. (I doubt if the cleaning had anything to do with the following).
I put a piece of stock in the chuck and decided to check it with an indicator. To my shock, the outer end (about 8") was out by .006"! Moving the indicator close to the chuck dropped the reading to about .003". This chuck has always held work to just under .001" since I bought it new, so I began looking for the error. The jaw gripping surfaces themselves show no burrs or scars.....in fact they still look new. I took the jaw tops off and discovered some minor hardened oil under them from being changed, depending on the work to be done. Okay, using 0000 steel wool and WD40 I gently removed the crud down to the ground surface and reinstalled the tops. Same readings, no change at all. I removed the entire chuck and examined the backing plate/spindle threads. Nothing unusual at all.
It might be possible (although I doubt it) that I inadvertently switched the jaw tops (or the jaws) at some point. Hard to believe, as I change them one at a time, but it's the only possibility left that I can think of. Could that possibly induce an error? Before I play "swap a jaw" I thought I'd ask and see if anyone had suggestions. If not, it may be my first experience with grinding chuck jaws.
I have a 1920 Hendey lathe that I rebuilt some years back and it's served me very well. It has a 10" Chinese 3 jaw mounted, which has always been very accurate. Or at least it was. The chuck started exhibiting signs that it needed to be cleaned so I disassembled it, cleaned everything and reassembled it. Note that Quan Lee (or whoever) mis stamped the jaw numbers, but it was assembled so that all three jaws meet on center. (I doubt if the cleaning had anything to do with the following).
I put a piece of stock in the chuck and decided to check it with an indicator. To my shock, the outer end (about 8") was out by .006"! Moving the indicator close to the chuck dropped the reading to about .003". This chuck has always held work to just under .001" since I bought it new, so I began looking for the error. The jaw gripping surfaces themselves show no burrs or scars.....in fact they still look new. I took the jaw tops off and discovered some minor hardened oil under them from being changed, depending on the work to be done. Okay, using 0000 steel wool and WD40 I gently removed the crud down to the ground surface and reinstalled the tops. Same readings, no change at all. I removed the entire chuck and examined the backing plate/spindle threads. Nothing unusual at all.
It might be possible (although I doubt it) that I inadvertently switched the jaw tops (or the jaws) at some point. Hard to believe, as I change them one at a time, but it's the only possibility left that I can think of. Could that possibly induce an error? Before I play "swap a jaw" I thought I'd ask and see if anyone had suggestions. If not, it may be my first experience with grinding chuck jaws.