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Screwcutting

Home › Forums › Workshop Techniques › Screwcutting

Viewing 7 posts - 1 through 7 (of 7 total)
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  • 4 February 2017 at 19:42 #282423
    Speedy Builder5
    Participant
      @speedybuilder5

      I was making some 3/8" x 32 tpi screw thread in phos bronze the other day, Top rake 0 degrees, plunge cut, cutting speed very low (as I was threading up against a shoulder). All was going well using no lubricant, then for the last couple of cuts, I used a threading compound and the surface finish went from 'not bad' to 'sharp as blazes' and torn.
      Fortunately I was able to clean the thread up after washing off all the cutting fluid and going back to cutting dry.
      What would others have used?
      BobH

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      4 February 2017 at 19:42 #15908
      Speedy Builder5
      Participant
        @speedybuilder5

        Screwcutting Phos Bronze

        4 February 2017 at 20:01 #282425
        roy entwistle
        Participant
          @royentwistle24699

          I would have cut it dry

          4 February 2017 at 20:06 #282426
          Neil Lickfold
          Participant
            @neillickfold44316

            I suggest to cut dry with an air blow, or flood coolant. You need to remove the micro swarf away, so that it does not get to try and jam between the tool and work surface. That is the most likely cause for the bad surface finish. A lot of industrial machines, cut from the back and the tooling is effectively upside down, Gravity aides is getting the chips away from the cutting edge. Normal home hobby lathe set up, gravity has the chips staying on the cutting tool surface.

            Neil

            4 February 2017 at 20:18 #282428
            Anonymous

              I screwcut a load of internal and external threads when making my water pumps in brass, gunmetal and bronze; both 32 tpi and 19 tpi:

              water pumps me.jpg

              All cut dry and no problems with surface finish, even when taking spring cuts. All threads were cut using insert tooling and at 260rpm.

              For HSS tooling I'd add a little top rake for bronze.

              Andrew

              4 February 2017 at 20:26 #282430
              JA
              Participant
                @ja

                I was never a manufacturing engineer but I know what would be said by those I worked with, "what ever works best". They frequently used trial and error to find out how to machine difficult materials. In other words not all of industry know the best way to deal with such things.

                If in doubt try a trial or more first.

                JA

                5 February 2017 at 04:40 #282454
                Hopper
                Participant
                  @hopper

                  I never use lube or fluid on brass or bronze. You might find it helps too if you don't plunge cut but either set the top slide to slightly under half the thread angle, or keep the top slide in the parallel to lathe axis position and advance it by 50 per cent of the depth of cut each time.

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