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  • leadscrew material choice

    What would the best choice of material be to make a tailstock leadscrew for a southbend 9.?Also could one choose a metal that one could harden so that a tap can be made at the same time. ? I find the carbon steels are hard to machine with hss, unless Im doing something wrong.
    Would brass work for a nut as its hard to get pb here .
    Could one use a v type thread for this or is v a bad choice of thread for this application.

  • #2
    Without access to the vast range of material readily available in the US, I'd use silver steel. There shouldn't be any problem machining it with HSS tooling, though I have noticed a tendency in recent years for it to have a tough skin, about 0.030" deep, which machines badly. Once you are through this its fine.
    If this is for home, not semi commercial use, you'd be fine using brass for the nut and a vee form thread.
    'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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    • #3
      When you say tailstock leadscrew, are you talking about the screw thats used to advance the tailstock quill? Assuming so, but never hurts to ask

      Id imagine that just about any steel would work alright for that. I wouldnt consider wear to be too much of an issue, given the rather small amount of movement a tailstock sees in comparison to something like the lathes actual leadscrew. Id probably grab something thats stable, easy to work with and somewhat wear resistant. Maybe something like 1144? Pretty tough, somewhat hard, should be a good option. I doubt theres any reason you couldnt/shouldnt go with something hardenable so you could make a tap from the same material. For that, id grab something like A2 drill rod. Easy enough to harden, plus it doesnt tend to warp much during heat treat

      Brass should work alright for a nut. Probably wont last as long as a good phosphor bronze, but again, pretty low movement application so brass should still last a good long time. Could also go with cast iron, if youre planning on using a hardenable material. Hardened screw running in a cast iron nut should last just shy of forever

      Wouldnt want to use a V thread in this application. With my luck, id end up putting a tiny bit too much force on the screw during drilling and muck something up. Rather have ACME threads for something like this, but overall i doubt its really necessary. I just have horrible luck and so overengineer everything

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      • #4
        Lots of "best" choices but almost any steel will work acceptably. Important part is to make the nut from different material than screw. Bronze, cast iron, brass (or even plastics).

        Same with the trapezoidal vs. 60 degree V-thread... V-thread is not "best" but works probably enough well in hobby use SB9.
        V-thread has higher friction and for same diameter/pitch it looks like you lose about 1/3 of efficiency compared to trapezoidal/acme.
        Acme might be 30% efficient and 60 degree V is 20% efficient if I managed to scramble correct equation to excel.
        Location: Helsinki, Finland, Europe

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        • #5
          Originally posted by plunger View Post
          What would the best choice of material be to make a tailstock leadscrew for a southbend 9.?Also could one choose a metal that one could harden so that a tap can be made at the same time. ? I find the carbon steels are hard to machine with hss, unless Im doing something wrong.
          Would brass work for a nut as its hard to get pb here .
          Could one use a v type thread for this or is v a bad choice of thread for this application.
          4140ph? If you need a bar pay shipping please. JR


          My old yahoo group. Bridgeport Mill Group

          https://groups.yahoo.com/neo/groups/...port_mill/info

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          • #6
            Originally posted by MattiJ View Post
            Lots of "best" choices but almost any steel will work acceptably. Important part is to make the nut from different material than screw. Bronze, cast iron, brass (or even plastics).

            Same with the trapezoidal vs. 60 degree V-thread... V-thread is not "best" but works probably enough well in hobby use SB9.
            V-thread has higher friction and for same diameter/pitch it looks like you lose about 1/3 of efficiency compared to trapezoidal/acme.
            Acme might be 30% efficient and 60 degree V is 20% efficient if I managed to scramble correct equation to excel.
            what do you mean by "efficient"? radial torque vs. thrust, somehow? for the same pitch?

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            • #7
              If I got EN 19 can it be hardened by torch and will it get hard enough to cut a brass nut. I think it only gets to rc 35 hsrdness.

              Is it even necessary if Im doing one tap in brass. EN 19 is 4140 in my neck of the woods and is easy to get.

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              • #8
                Originally posted by dian View Post

                what do you mean by "efficient"? radial torque vs. thrust, somehow? for the same pitch?
                output energy/input energy. 70% of energy is lost to friction and only 30% goes to actual work.

                For same pitch it is also related to torque needed for same thrust.
                60 degree V-thread needs 50% more torque than trapezoidal to generate same amount of axial thrust.

                Again, typically not huge issue on a hobby lathe tailstock.
                Location: Helsinki, Finland, Europe

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                • #9
                  Originally posted by plunger View Post
                  If I got EN 19 can it be hardened by torch and will it get hard enough to cut a brass nut. I think it only gets to rc 35 hsrdness.

                  Is it even necessary if Im doing one tap in brass. EN 19 is 4140 in my neck of the woods and is easy to get.
                  You should be able to get EN19 to something like 55 rc with water quench. Make the tap enough long with gradual taper and it should last better.
                  Location: Helsinki, Finland, Europe

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                  • #10
                    Originally posted by plunger View Post
                    What would the best choice of material be to make a tailstock leadscrew for a southbend 9.?Also could one choose a metal that one could harden so that a tap can be made at the same time. ? I find the carbon steels are hard to machine with hss, unless Im doing something wrong.
                    Would brass work for a nut as its hard to get pb here .
                    Could one use a v type thread for this or is v a bad choice of thread for this application.
                    If you find smooth shafts from old office copying or printing equipment in A2 format, then try making them.
                    I made my screws and nuts from such shafts, I had them of different diameters from 6 to 14 millimeters. They are excellently machined and made of steel with good antifrictional properties.
                    Unfortunately, the steel grade of these shafts is unknown to me.
                    p.s. Excellent machining with hss cutter.
                    Ivan.
                    Last edited by pensioner; 09-05-2020, 08:12 AM.

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                    • #11
                      Originally posted by MattiJ View Post

                      output energy/input energy. 70% of energy is lost to friction and only 30% goes to actual work.

                      For same pitch it is also related to torque needed for same thrust.
                      60 degree V-thread needs 50% more torque than trapezoidal to generate same amount of axial thrust.

                      Again, typically not huge issue on a hobby lathe tailstock.
                      how much is a ball screw?

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                      • #12
                        Originally posted by dian View Post

                        how much is a ball screw?
                        Around 90%
                        https://tech.thk.com/en/products/pdf/en_b15_006.pdf
                        Location: Helsinki, Finland, Europe

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                        • #13
                          Most all of the screws on my south bend seem to be made of ordinary mild steel, not hard at all. It works ok because the nuts are bronze.

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                          • #14
                            When i started my shop I made a few bushings out of brass, their performance was disappointing..
                            save yourself the trouble use bronze. It takes like maybe 1/2 hour to make a single point tool to thread the bronze piece.
                            Last edited by 754; 09-05-2020, 10:20 AM.

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                            • #15
                              Hi,

                              Last tailstock screw and nut I made, 13x36 LeBlond, I used 1018 for the screw and aluminum bronze for the nut. Just materials I had handy. It's not a huge deal what materials you use.
                              If you think you understand what is going on, you haven't been paying attention.

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