Taper on connecting rod

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Taper on connecting rod

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  • #10142
    Richard Brickwood
    Participant
      @richardbrickwood17062
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      #461130
      Richard Brickwood
      Participant
        @richardbrickwood17062

        Hello – I want to reduce the diameter of a connecting rod from 1/4" to 3/16" over a distance of 1".

        I've tried setting ther topslide over but it still cuts almost parallel even at 10 deg. I've tried from 2.5 deg upwards.

        What am I doing wrong?

        #461132
        Nigel Bennett
        Participant
          @nigelbennett69913

          Are you actually twiddling the topslide handle rather than moving the carriage?

          #461134
          Anonymous

            The angle needed on the topslide is about 1.8 degrees. So I suspect a set up problem. A picture would be helpful. Less likely is that the work is deflecting. Is the turning exactly parallel or just close?

            Andrew

            #461136
            Richard Brickwood
            Participant
              @richardbrickwood17062

              Hi Nigel – nope – moving the carriage.

              Hi Andrew – things to do when not gliding! -, I thought it was about 1.8 degrees offset but got very little change in diameter over the 1". Luckily using scrap BMS as test pieces rather than castings! 'Almost' parallel is about 5 thou.

              #461141
              roy entwistle
              Participant
                @royentwistle24699

                Moving the carriage is your problem

                #461144
                old mart
                Participant
                  @oldmart

                  Turn the topslide 1.8 degrees anticlockwise from zero as Andrew suggests. Set the tip of the tool right next to the end of the work. The work should project the minimum possible from the chuck, say 1 1/8". Lock the carriage (saddle) if you can. Then adjust the cross slide to allow small cuts using the top slide. Each cut should reach a little closer to the chuck. Don't try to cut too deeply, or the work will probably bend with the force. Test on scrap metal until you get good at it. Good luck.

                  #461154
                  Mick B1
                  Participant
                    @mickb1

                    As said above, you certainly need to run the tapered cut with the topslide, not the carriage.

                    Consider whether you could put a hole in the little end to use with a running centre for tailstock support. If you can, it might still be a fiddle to create clearance to turn the topslide handwheel, but tailstock support would make turning a taper on the conrod a good deal safer.

                    #461163
                    Anonymous
                      Posted by Richard Brickwood on 30/03/2020 20:38:33:

                      Hi Andrew – things to do when not gliding!

                      Sounds like you've got the taper issue sorted. Could be a lack of currency? smile

                      I'm probably the most current pilot at Gransden as I flew my DG200 the Thursday before last (20th) at Milfield where I was retrieving it, fortunately just before the lockdown kicked in.

                      Andrew

                      #461229
                      Richard Brickwood
                      Participant
                        @richardbrickwood17062

                        …………..this all makes sense – thank you: will spend a happy afternoon turning BMS into swarf – and let you know the results.

                        RIB

                        #461237
                        John Hinkley
                        Participant
                          @johnhinkley26699

                          Richard,

                          Glad you've got your taper turning sorted. However, I'd be inclined to investigate why your lathe is turning an (albeit slight-ish) taper of 5 thou over a distance of one inch when just using the carriage? Unless I've gotten the wrong end of that particular stick.

                          John

                          #461492
                          Richard Brickwood
                          Participant
                            @richardbrickwood17062

                            ..thank you all for responding – the problem was definately feeding using the carriageto feed instead of the top slide.

                            Made one from scrap yesterday – perfect (well amost) – more practice today.

                            John – re your comment on the slight taper – it was my measuring error and poor recollection when writing: the real error is negligible – something like 0.0001 – but thanks for the suggestion.

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