Slowly Fixing old war wea lathe, worn cross slide screw.
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  1. #1
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    Default Slowly Fixing old war era lathe, worn cross slide screw.

    well, spent the weekend tearing apart my carrage and cross slide feed to find the nut on the shaft a little weird. someone was in here before and made it oversized 5/8"-8 acme thread. UGH, 0.675" od and 0.125" tooth spacing which had a brass nut that had 0.030 of play to it. So this will be going to another local shop to get fixed at least as I dont have a working lathe to use or the tooling to do it in. Hopefully the bill doesn't hurt too bad, will probably have it made from bearing bronze instead of the brass they used.

    also found hammer marks all over the turret mount that they used and wedged into the cross feed top ffs..... hopefully the previous idiot that owned it didn't weld it all in.
    Last edited by BT Fabrication; 03-31-2021 at 07:43 AM.

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    I have a guess as to what happened. The maximum major diameter for an INTERNAL 5/8-8 acme thread is .6650. If they made the nut first using a hand ground bit they could easily have cut beyond the maximum major diameter, and still have been within specifications with regard to the pitch diameter by a go/no-go guage. If they then cut the male threads to fit, the major diameter would be oversize, with the pitch diameter measured by thread wires being within specifications.

    They may have cut them oversize on purpose. Why? This increases with surface area on the thread flanks, spreading the wear over a larger area, meaning it will take longer for excess backlash to develop. If they had made the thread to specifications, you would have more than .030 play in the nut.

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    could be right, looked like they cut the internal threads and kept cutting to make it fit as there is multiple tooling marks in the nut at the maximum major diameter for the crest of the thread.

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    Buy a new screw and nut. I usually cut the handle end off drill and ream a hole in it and then turn down one end of the new screw and press it into the hole in the old handle. Then drill and ream a taper hole in them and use a taper pin to hold them together. You can machine the new nut too. Green Bay Manufacturing

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    Its an odd shape, I have a piece of solid bearing bronze stock to make a new one from, then tap a hole and possibly make a new shaft.
    shaft isnt part of the handle, threaded on one end, the other goes through the slide with a keyway for the handle and a nut.


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