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Internal threads - setting zero

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  • Internal threads - setting zero

    I was recently cutting some 60 tpi internal threads in a .400-in bore and I had a helluva time finding where the tool just touched the ID so I could set zero on the cross-slide. It's pretty touchy when the entire thread depth is only about .009-in.

    I ended up turning the chuck by hand and slowly cranking the cross-slide until I could hear a faint scratching. My ears are still pretty good - a lot better than my eyes. Anybody got any tricks?

  • #2
    I use a Sharpie to put a little ink in the hole. When you see the ink being removed by the cutter, you're there.

    Andy Pullen
    Clausing 10x24, Sheldon 12" shaper, Clausing 8520 mill, Diacro 24" shear, Reed Prentice 14" x 34"


    • #3
      As Andy said, Sharpie, Dykem, any color that will show a scratch.

      Use of a pen light or flashlight might help to see the scratch in small bores.
      Paying Attention Is Not That Expensive.


      • #4
        If I have the room, I counterbore the part to the major diameter for a sixteenth inch depth or so.

        When the threading tool just scrapes the counterbore, your thread is to depth.

        Give it an extra thou and a spring cut.



        • #5
          I grind the tool "backwards", set it to cut on the "back side" of the hole, run the lathe in Reverse and pull the cut towards the Tailstock, setting the compound accordingly. That way, I can more closely observe the progress of the cut.


          • #6
            Thanks guys. The ink would make it easier to see; and I like Kap's idea of setting for final depth.