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Internal threading compound won't do it

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  • Internal threading compound won't do it

    Hello

    I am wanting to turn some internal threads, and have run into an issue. My compound won't rotate enough to get me to 29.5°.

    What should I do? Just cut them straight and advance with the cross slide?

    Thanks!

  • #2
    Can you reverse the toolpost, or invert the threading tool?
    Can you post more info on the lathe and toolpost in question?

    Comment


    • #3
      You have 4 positions for setting the compound depending on left or right hand threads. Can you set the compound 180° from normal?

      Bob

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      • #4
        on my cross slide there is a large nipple that prevents the compound from rotating that far. I was unable to cut a 60° dead center from that end of the compound. My lathe also doesn't go in reverse (I converted to single phase from 3 phase, and don't know how to wire the drum switch to give me a reverse on the motor), so inverting the tool won't help.

        I guess I can just advance straight in, and take it real slow?

        Comment


        • #5
          With the compound at 90 degrees to the cross slide, advance the compound half the distance you advance the cross slide. This will advance down a 60 degree thread flank similar to angling the compound. Works for inside or outside threading.

          Idea from Martin Cleeve's "Screwcutting in the Lathe", I now use this method for all my threading.

          John

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          • #6
            With the lathe running forward, the tool inverted and cutting on the back side you will be cutting a right hand thread.

            Bob

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            • #7
              Ok, great ideas, I think I will end up trying both of those methods. Sorry, that makes sense now Bob, appreciate it!

              Dave

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              • #8
                Being a bit old and thick, perhaps I have missed the point. My topslide stays at the same angle for external, internal,right and left hand threads. Theoretically there are top rake angle deficiencies with this but practically, it works OK.

                IanR

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                • #9
                  Not wanting to ruffle any feathers here, but the compound is just as happy "pulling" as it is "pushing".

                  I find it hard to believe that you can't swivel the compound axis 30° from the cross slide axis.

                  Dave

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                  • #10
                    Some compounds have spring loaded indexing pins that latch when the compound is rotated one way ,but can be rotated 360 degrees freely the other way. It could be that your latch pin is facing sideways or something.
                    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                    • #11
                      Originally posted by becksmachine
                      Not wanting to ruffle any feathers here, but the compound is just as happy "pulling" as it is "pushing".

                      I find it hard to believe that you can't swivel the compound axis 30° from the cross slide axis.

                      Dave
                      My experience also!

                      Comment


                      • #12
                        Getting screwed in reverse

                        Originally posted by DebosDave
                        Hello

                        I am wanting to turn some internal threads, and have run into an issue. My compound won't rotate enough to get me to 29.5°.

                        What should I do? Just cut them straight and advance with the cross slide?

                        Thanks!
                        You don't say what size the thread is or whether it is a "through" thread or "blind". If its "blind" its all too easy to "crash" at the bottom of the hole before you can disengage the half nuts.

                        As it seems that you don't have any problems with setting the top/compound slide for external threads and that you are happy with using that set up - then keep using it.

                        Set your threading tool "right side up" - as normal - (and on centre), run the lathe in reverse and start the thread at the bottom of the hole - engage your half nuts and start screwing starting at the bottom of the hole and screwing toward the tail-stock.

                        It may seem counter-intuitive but it works, its safer, you have a better view of the cut and your set-up works for both internal and external threading.

                        If the thread is "blind", you will need a groove to start from.

                        I'd suggest marking your lathe bed (pencil will do) where the carriage/saddle needs to be to start the groove and set the carriage/saddle to/at that point after the tool is in the starting groove, engage the half nuts and away you go.

                        Comment


                        • #13
                          Originally posted by becksmachine
                          Not wanting to ruffle any feathers here, but the compound is just as happy "pulling" as it is "pushing".

                          I find it hard to believe that you can't swivel the compound axis 30° from the cross slide axis.

                          Dave
                          I am going to see if I can pull it also. I am worried that my setup is too close to the chuck to do it, but am going to see tonight. The thread size is 5/8" x 24tpi. It is through threading, about 1" deep. The cutter is pretty small, so is the stock, so the carriage will be right down there close to the chuck. Will see if there is enough clearance later.

                          Thanks for all the input.

                          Comment


                          • #14
                            A 24 pitch thread isn't very heavy. If you can't swing the compound the way you need don't sweat it, just feed straight out. Compensate for the slightly heavier chip load by taking more passes of lighter depth of cut. Probably 2 or 3 extra passes, no big deal.

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                            • #15
                              Unscrew the nipple.

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