Cutting BSPT threads with a die

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Cutting BSPT threads with a die

Home Forums Beginners questions Cutting BSPT threads with a die

  • This topic has 15 replies, 17 voices, and was last updated 2 June 2015 at 11:09 by Alan Wilkinson 1.
Viewing 16 posts - 1 through 16 (of 16 total)
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  • #7599
    Anonymous
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      #188293
      Anonymous

        I want to replicate two radiator bypass hose connectors on a Suzuki Kettle I'm restoring in 303 stainless. They're 1/4" and 3/8" BSPT threads and I've never had to do taper threads before.

        Do I just turn the bar parallel to the major thread diameters or should I be using the top slide to taper them up to the major diameter before using the die?. I have looked it up and know the sizes but I can't find any reference as to which is the best way to do things. The taper is 1 in 16 which would mean an angle of 1.5 ish degrees so would have to be a good guesstimate if I did it that way.

        Edited By Mick Berrisford on 01/05/2015 12:31:46

        #188295
        Brian Wood
        Participant
          @brianwood45127

          Hello Mick,

          I have not cut tapered threads before, but I believe the male part of the thread, the tapered section in other words, is cut at right angles to the taper face, as would be the case with any other thread cut on a component..

          That means you will need to follow the taper with the threading tool and doing that mechanically means using a taper turning attechment, having first machined the taper using the attachment.

          I don't see how such a tapered thread can be cut with a die, parallel threads yes, but not taper.

          Sorry I can't give you more information than that.

          Brian

          #188296
          Tony Pratt 1
          Participant
            @tonypratt1

            Brian is correct, you really need a taper turning attachment.

            Tony

            #188297
            Gordon W
            Participant
              @gordonw

              I've never tried to cut a taper thread either. The mating female thread will be a straight thread ( usually) . Easiest is just use a parallel male thread and sealer or washer.

              #188298
              S.D.L.
              Participant
                @s-d-l

                Posted by Mick Berrisford on 01/05/2015 12:29:53:

                I want to replicate two radiator bypass hose connectors on a Suzuki Kettle I'm restoring in 303 stainless. They're 1/4" and 3/8" BSPT threads and I've never had to do taper threads before.

                Do I just turn the bar parallel to the major thread diameters or should I be using the top slide to taper them up to the major diameter before using the die?. I have looked it up and know the sizes but I can't find any reference as to which is the best way to do things. The taper is 1 in 16 which would mean an angle of 1.5 ish degrees so would have to be a good guesstimate if I did it that way.

                Edited By Mick Berrisford on 01/05/2015 12:31:46

                Do as you suggest turn taper first then cut with BSPT die.

                Steve

                #188299
                Jeff Dayman
                Participant
                  @jeffdayman43397

                  I've always cut tapered pipe threads with a die, whether with a die in the lathe under power or out by hand.

                  Pipefitters cut threads on millions of pipe ends around the world every day , and I've yet to see one do a cut taper thread in an engine lathe. Powered pipe threaders with dies, yes, engine lathes, no. JD

                  #188300
                  Russ B
                  Participant
                    @russb

                    I don't see any problem die cutting a taper, I guess the only tricky bit is ensuring the taper die is not driven to deep or the threads will bottom out before they seal.

                    From my engineering handbook, the gauge plane and diameter at that plane that your aiming for are (for external threads)

                    for the 1/4"
                    Gauge plane 0.237" from end face
                    Major Diameter at that point 0.518"

                    for the 3/8"
                    Gauge plane 0.250" from end face
                    Major Diameter at that point 0.656"

                     

                    I would guess the complete, incomplete and washout thread will dictate itself given the above depending on the OD of the pipe. For reference I've never heard of the taper being pre machined and I know the guys  I work with just cut straight on to parallel pipe! I'm certainly not suggesting its the right way to go about things, but it seems to work for them.

                     

                     

                    Edited By Russ B on 01/05/2015 14:53:58

                    Edited By Russ B on 01/05/2015 14:57:07

                    #188302
                    JasonB
                    Moderator
                      @jasonb

                      With the big hefty pipe threaders there is no need to put a taper on the pipe but if its a small split die then even 3/8BSP parallel needs quite a bit of elbow grease so cutting a small taper for BSPT will just make the job a bit especially on stainless.

                      Also worth remembering that the pipe threading kit tends to have a guide to keep the die head true which you won't get on a split die so again a bit of a taper will help things along.

                      This is what I sometimes use on the models especially exhaust pipes on the hit & miss ones, this is 3/8BSPT

                      imag3749.jpg

                      Edited By JasonB on 01/05/2015 15:12:23

                      #188319
                      nigel jones 5
                      Participant
                        @nigeljones5

                        are the male and female threads tapered? Or is it always one or the other?

                        #188321
                        JasonB
                        Moderator
                          @jasonb

                          Usually parallel internal and tapered external.

                          #188323
                          Jon Gibbs
                          Participant
                            @jongibbs59756

                            I'd have thought you could single point thread it between centres fairly easily with the tailstock set over?

                            Jon

                            #188329
                            Brian Wood
                            Participant
                              @brianwood45127

                              Hello Jon,

                              The thread will then no longer be at right angles to the face of the material, it might not matter a lot but it will also distort the thread pitch angle as well

                              Brian

                              #188336
                              Jon Gibbs
                              Participant
                                @jongibbs59756

                                Brian,

                                Can you not set the tool perpendicular to the axis of the taper rather than the surface of the taper?

                                I'd have thought that would result in the thread being cut right or an I missing something?

                                Jon

                                #188352
                                Hopper
                                Participant
                                  @hopper

                                  Usual way when threading pipe is to run the die straight on to the pipe. No taper put on pipe first. The size you are working on, the amount of taper is not going to be much.

                                  An old pipefitters' dodge is if you have trouble getting the die started on the cut, put a small hacksaw nick on the very end of the pipe to let the first teeth of the die get some "bite". That is usually only needed on larger pipe, 2" etc. But if you are using stainless, you know how uncooperative a material it can be, so it might help.

                                  Edited By Hopper on 02/05/2015 01:07:13

                                  #188364
                                  Brian Wood
                                  Participant
                                    @brianwood45127

                                    Hello again Jon,

                                    Setting the tool perpendicular to the tapered face as you suggest doesn't overcome the basic problem of the geometry of tool travel down the axis of the lathe across an angled surface.

                                    Draw a sketch on paper to see what I mean

                                    Brian

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