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worm gears

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  • worm gears

    Does anyone have experience cutting a gear for a worm using the following method. Chucking the acme tap in a lathe, held between the chuck and tail stock, while holding the gear blank on the cross slide. The tap will rotate the gear as it cuts the thread, as you crank in the cross slide.
    While I know this works in a pinch, I was wondering how good of a gear can be achieve with this method.

  • #2
    Have a look at this link:
    I haven't tried this, but it is well written and will give you some background. There is a similar article in back issues of HSM or MW. In that article an ordinary tap was modified and used with a jig to do as you suggest. If I can find it I will post the reference here.

    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
    ~Practitioner of the Electromechanical Arts~


    • #3
      I have done this sucessfully by gashing it first with a cutter, even a single point cutter a little les in depth than finish. This used to be the standard procedure for horizontal mills in making worm wheels. The setup you describe is basically the same.


      • #4
        wes is correct if he and I are thinking of same project. Its in "projects one" page 84, author is theodore clarke. Neat thing about the clarke scheme was that he used the frame holding the shft to ridgidly hold his tap while cutting the gear teeth. The question concerned holding the tap between centers and cross feeding the gear into the tap. Neversaw it done nor heard of it but if the gear blank is backed up well, held down firmly, free to rotate- it looks to me as though it would cut the gear to fit the tap. I have no idea about how pressure angles etc would work out. So for light duty application, not continous running, the quality is probably adequate to excellent! How you gonna know if you don't try and apply?


        • #5
          Walt suggests gashing first, I would do this myself. Gash at the helix angle of the threads with a cutter ground with around .010 larger swept diameter than tap, take to minor diameter or close to it.

          I've made worm gears this way without use of tap that worked, running against a tap will generate proper form to teeth. Without this hobbing one just cuts a bit loose and hopes for the best with the run in.