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[IMG] Turning threads in steel: badly torn finish with ground and honed HSS

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  • #46
    If the material is tearing, allow .15mm for 3 or 4 finishing passes, it can clean up a lot of bad looks.
    I never measure the angles of the side of my handground tool just the 60 degree part. Hold it to the work or another thread to see if it needs more clearance ..then when you hone you do a thin edge, NOT the WHOLE side.
    Then when you touch up the tool later it's quicker.
    I love threading I finally bought insert tooling for OD threadin
    My lathe Had a very nice gearbox, easyvto use. I can remember setting up to thread say 3/8 or 1/2 inch, a short thread.. 8 minutes start to finish, for 1st thread.

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    • #47
      Originally posted by J Tiers View Post
      Be careful with back rake, as that is what changes the effective cutting geometry, and thus the actual angle of thread that you cut.

      Any time the top of the tool is not perfectly radial to the work, you will have a change of geometry vs what is ground into the tool. The more off of radial, the larger that effect is.
      I realize this, and have already tested the geometry against a known good bolt, and the flank angles of the thread are by eye pretty close.


      Originally posted by 754 View Post
      If the material is tearing, allow .15mm for 3 or 4 finishing passes, it can clean up a lot of bad looks.
      I never measure the angles of the side of my handground tool just the 60 degree part. Hold it to the work or another thread to see if it needs more clearance ..then when you hone you do a thin edge, NOT the WHOLE side.
      Then when you touch up the tool later it's quicker.
      I love threading I finally bought insert tooling for OD threadin
      My lathe Had a very nice gearbox, easyvto use. I can remember setting up to thread say 3/8 or 1/2 inch, a short thread.. 8 minutes start to finish, for 1st thread.
      0.15 mm. sounds to me like a lot for a finishing pass. That's more like what I use for roughing. I guess you ment 0.015 mm?



      At any rate, the problem is now mostly solved. I threaded a piece of mystery mild steel near 48 mm. OD @ 180 RPM with a 2.0 mm. pitch and had success. I also found me a ~60 mm. piece of some kind of harder mystery steel, perhaps chromium-molybdenum-alloy and also had success, AFTER losing the cutting edge once due to too high surface speed. I ended up at 90 RPM at this diameter and kept the edge throughout. I did not nearly get a mirror finish, but highly serviceable. Thank you all for your suggestions throughout this tough, trying time. I took ~20 minutes worth of uncommented video with my GoPro, let me know if you want to see this.

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      • #48
        What I mean was 3 or 4 passes to do the last 6 thou,,or .15mm.
        The blue chips in your last pic, were those from threading, if so, too fast.

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        • #49
          Originally posted by 754 View Post
          What I mean was 3 or 4 passes to do the last 6 thou,,or .15mm.
          The blue chips in your last pic, were those from threading, if so, too fast.
          Oh, now I get it.

          Those blue chips came from carbide tooling doing the undercut and turning and facing. When first threading this harder steel i got some dark gold / light brown chips and lost the cutting edge right after. Too fast, no doubt.

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          • #50
            Looks typical of HR or material with poor machining characteristics or too much give in the tool / holder etc.
            Try cutting them on a piece of brass or alum and see what you get. Process of elimination.

            JL................

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