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SB 9" lathe compound screw

CharlieR

Plastic
Joined
Aug 27, 2017
I have a mid fifties sb 9" mod A lathe. The compound moves .063" on one complete revolution of the dial. Small dial. I would think it would move .100 since the dial is graduated 100. Any thoughts on why it moves less than .001 per graduation? Could a special screw have been installed or provided originally in the lathe?
 
My first metal lathe was bought new in 1954 and had 3/8-24 feed screws on the cross and compound. But it also had no dials, so there was no confusion trying to read dials with strange numbers of thousandths on them. Proper lathes do have dials and feed screws with pitches that allow more or less convenient numbers of thousandths on the dials, like 25, 50, 100, 200 or 250. I have machines with all five of those dial types.

So, like Steve said, pull the screw out and see what thread you have. I have seen very worn feed screws with no hint of the original thread form in the worn portion. Even then, the original pitch is easy enough to measure and the thread form is still intact at the ends.

Larry
 
OK. Checked the compound screw. 3/8"-16 TPI. My guess is someone replaced the original screw at some point in time. The screw has very little wear if any. I think mystery is resolved. Lunch was good.
 








 
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