Threading with inserts

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Threading with inserts

Home Forums Hints And Tips for model engineers Threading with inserts

Viewing 14 posts - 1 through 14 (of 14 total)
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  • #454463
    David Colwill
    Participant
      @davidcolwill19261

      I can't decide if this is a tip, a question or just an observation.

      I have to do a fair amount of threading and often use the ER16 type inserts.

      I have noticed that the threads can look quite rough and then suddenly as you get to correct depth magically get much better.

      Has anyone else noticed this?

      If they have do they know why?

      I post this here as I have seen people complain that they don't get good results and wonder if this is why.

      I should point out that I don't use angled infeed on the manual lathe but do on the CNC.

      I also it doesn't seem to be a depth of cut issue because when doing batch work I am going off the DRO and am able to finish the thread with 1 spring pass.

      Any thoughts?

      Regards.

      David.

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      #30731
      David Colwill
      Participant
        @davidcolwill19261
        #454467
        KWIL
        Participant
          @kwil

          I always use angled feed, having found that with straight in, the chips from the two faces seem to cause problems until, as you say, the final cut. Full thread or partial inserts?

          #454473
          David Colwill
          Participant
            @davidcolwill19261

            I use full thread inserts 99% of the time.

            I'm not cutting anything bigger than 10 tpi and mostly its 16tpi or finer.

            #454474
            JasonB
            Moderator
              @jasonb

              Could simply be the second "tooth" of the full form insert is doing a fine finish cut as well as rounding off the crests which will take off any burr from earlier passes

              I was looking at suggested cutting criteria the other day for a threading insert and the DOC decreased as you got closer to the final pass so may also be worth looking up what is suggested for the particular inserts you are using.

              #454484
              David Colwill
              Participant
                @davidcolwill19261
                Posted by JasonB on 27/02/2020 11:31:42:

                Could simply be the second "tooth" of the full form insert is doing a fine finish cut as well as rounding off the crests which will take off any burr from earlier passes

                I was looking at suggested cutting criteria the other day for a threading insert and the DOC decreased as you got closer to the final pass so may also be worth looking up what is suggested for the particular inserts you are using.

                Interestingly not all insets have the second tooth. The photo shows two 1.5 mm pitch inserts…

                img_20200227_124304.jpg

                As to the depth of cut. I suspect that I err on the side of caution. I seem to have stopped looking at manufacturers data for cutting speeds as this invariably spells disaster for me crying.

                Perhaps next time I'm doing some threading I should push one of these inserts and see what is possible.

                Another question. Has anyone tried resharpening one of these inserts? It looks like it should be possible to take some off the top of the insert and still leave the correct profile. I haven't tried this yet but I keep the dull ones in a drawer waiting for the time of desperation.

                #454499
                DC31k
                Participant
                  @dc31k

                  Posted by David Colwill on 27/02/2020 13:04:00:

                  Interestingly not all insets have the second tooth. The photo shows two 1.5 mm pitch inserts…

                  I hope I am not telling you something you already know, but are you aware that threading inserts come as full profile, suitable for only one thread pitch and as partial profile, suitable for a range of pitches?

                  Full profile ones look like that on the left, where the second tooth finishes the crests.

                  While both the inserts you show may be able to cut a 1.5mm pitch thread, only one of them is strictly a 1.5mm pitch insert.

                  Partial profile metric are usually labelled A60, G60 or AG60. Full profile will have a number for the pitch as part of their label.

                  #454510
                  Anonymous

                    Posted by David Colwill on 27/02/2020 09:42:12:

                    I have noticed that the threads can look quite rough and then suddenly as you get to correct depth magically get much better. Has anyone else noticed this?

                    Sometimes, on steel. Haven't seen it on cast iron or brass. I start with large depths of cut,up to 20 thou depending upon the thread pitch, and reduce DOC once I'm close to full depth. For stringy materials like steel it's possible the swarf on the first cuts rubs against the flanks as it tries to escape. With smaller DOC the swarf is smaller and thinner, so more pliable, and will have less of an effect on the flanks. For brass and cast iron where the swarf is fine particles the issue doesn't seem to occur. I do all my screwcutting by plunging straight in.

                    Insert profiles are rather more involved than DC31k propounds. Here are three inserts:

                    threading inserts.jpg

                    Which are full form and which partial?

                    The one on the left is marked 16ERAG60, so a partial profile for a 60 degree angle thread. The middle insert is marked 16ER-8W, a full profile insert for 8tpi Whitworth, where the partial tooth does indeed form the rounded crest, as specified in the Whitworth form. The righthand insert is marked ER16-2.0ISO, a full profile insert for 2mm pitch ISO threads. These threads have a flat crest, so the second tooth is not needed to fully form the crest, a flat is sufficient.

                    Andrew

                    #454538
                    old mart
                    Participant
                      @oldmart

                      Regarding sharpening this type of insert, I can think of two things. First, the height would be slightly lower, and second, they are probably tapered back slightly, so reducing the height would change the profile. The profile would reduce slightly, say from a true 28tpi to more like a 29tpi. This would only be true with full profile inserts, the partial profile ones are already a compromise for use with a range of pitches on non critical applications.

                      #454584
                      David Colwill
                      Participant
                        @davidcolwill19261
                        Posted by DC31k on 27/02/2020 16:13:23:

                        Full profile ones look like that on the left, where the second tooth finishes the crests.

                        While both the inserts you show may be able to cut a 1.5mm pitch thread, only one of them is strictly a 1.5mm pitch insert.

                        Partial profile metric are usually labelled A60, G60 or AG60. Full profile will have a number for the pitch as part of their label.

                        So you would think, however both of those inserts are labelled ER16 1.5 ISO and are listed as full profile.

                        #454585
                        David Colwill
                        Participant
                          @davidcolwill19261

                          Andrew,

                          Most of my work is in EN16T, which machines very well. I do reduce depth of cut as I get nearer to finished size but not in any scientific way smile p.

                          #454587
                          David Colwill
                          Participant
                            @davidcolwill19261
                            Posted by old mart on 27/02/2020 20:31:31:

                            Regarding sharpening this type of insert, I can think of two things. First, the height would be slightly lower, and second, they are probably tapered back slightly, so reducing the height would change the profile. The profile would reduce slightly, say from a true 28tpi to more like a 29tpi. This would only be true with full profile inserts, the partial profile ones are already a compromise for use with a range of pitches on non critical applications.

                            The centre height issue is something I could live with given I would only want to do it in an emergency. The second issue is the more important. Perhaps I should give it a go!

                            #454591
                            Anonymous
                              Posted by David Colwill on 28/02/2020 08:44:32:

                              Most of my work is in EN16T……………….

                              By coincidence the last thread I screwcut was M16x2 in EN16T, for a cutter drawbar. The finish is ok, but since I was cutting a metric thread on an imperial lathe I couldn't use my high speed threading attachment. I was running at slow speed, 85rpm I think. Here's the thread:

                              m16 thread.jpg

                              The thread is better than it looks, and works fine.

                              Andrew,

                              #454630
                              old mart
                              Participant
                                @oldmart

                                The full profile inserts will have the correct tip radius for the thread pitch, this is an important part of the specification for threads which have to be top quality such as for aircraft fastenings. My old firm would not have ever bought partial profile inserts for this very reason. They mostly cut UNJEF threads which have a non standard root radius which is better for fatigue life. For our general purposes, the partial profile inserts will still give superior results to die cut threads, but the difference is so small that only laboratory testing could tell the difference.

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