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Parting Off ???

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  • Parting Off ???

    I have the HSS cutoff blades with the top cutting edge beveled. My ? is if the highest part of the bevel be set dead on center? I have tried .030 thou above center, slightly above center, on center, and slightly below, and still have grabbing. It feels like the work piece is going to pull the toolholder underneath it at times.

    12x36 import lathe parting a 1" mild steel shaft. Tried rpm from 180-550, auto feed from the slowest up to about the fifth slowest. Turned the tool in by hand also. Any ideas? Thanks

  • #2
    I had one of those blades too, about 1" x 1/8", the only way i could get anywhere with it was to grind some rake on the top. It was still grabbing though.

    Shortly after a good spank-up with it, it bought a tipped parting blade and have never gone back.

    Really is the best tool i've bought yet.

    Dave
    If it does'nt fit, hit it.
    https://ddmetalproducts.co.uk
    http://www.davekearley.co.uk

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    • #3
      I second the idea of getting a carbide tipped part off blade. The ones with adjustable stick-out are super nice. One thing I found, get the .125 wide blade. I had a .093 wide blade, and it kept snapping out the insert. The .125 wide blade is way more rigid. I bought a Newcomer brand, and was very disappointed with it. Then I tried an Iscar blade, I think I have had the same insert in it well over a year.
      --Doozer
      DZER

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      • #4
        One problem might be the fact that you are trying to part mild steel. Mild steel is not free machining steel, mild steel is for welding projects. You need to get some free machining steel like 12L14 or 1215, try parting it and let us know how that works for you.
        Mark Hockett

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        • #5
          As I recently got flamed for here, make sure you are as close to the chuck as possible aka a couple of parting blade widths away from the chuck if you can get that close. I've also observed that some of the cheaper import parting blades are too soft to part anything of significance. I've had better luck with a brazed carbide parting tool but you still have to be as close to the chuck as possible with the work as well centered as possible (using the 4 jaw) if you want any sort of success.

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          • #6
            Your best bet is with the top of the blade flat and a very sharp edge. Any back rake or chip breaker in the top will cause it to dig in and cause damage. You need the top at center line 0 back rake and as square to the work as posible. You don't have to have much clearance on the front of the blade but you do have to have side clearance. HSS parting blades need a slow speed and lots of oil. If they dull it's crash city coming up. The major issue with the HSS blades is they are the same width from tip the the rear and that has no side clearance and is rubbing most the time. Any side movement can bind the blade.

            Parting can be an accident looking for a place to happen. It is best done with a straight line holder because the downward tool deflection can't stand any side movement of the blade.

            The first time I used a carbide insert parting blade I never looked back and while I still have the HSS holders I refuse to use them.

            Parting is no longer such sweet sorrow, it is now happiness and delight.
            Last edited by Carld; 03-02-2009, 04:22 PM.
            It's only ink and paper

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            • #7
              Originally posted by Mark Hockett
              One problem might be the fact that you are trying to part mild steel. Mild steel is not free machining steel, mild steel is for welding projects. You need to get some free machining steel like 12L14 or 1215, try parting it and let us know how that works for you.
              I have cut the heads off some 3/4" grade 8 bolts, and had a nice coil of chips coming off. I am not sure what metal grade 8 bolts are made from, but I had no problems parting them.

              I have looked at the Iscar blade type, but I don't have a QCTP, just a turret type tool holder.

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              • #8
                Big T, you can use the insert type in a turret type tool post. I did that for a long time untill I got my QCTP.

                Go back and read my post above your last post.
                It's only ink and paper

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                • #9
                  Parting off

                  It sounds as though there is insufficient rigidity in your cut-off tool, tool holder, tool post, and/or the work itself. Providing a positive rake reduces the cutting forces, hence the deflection. Try to make the entire set-up as rigid as possible while parting off.

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                  • #10
                    Originally posted by Carld
                    Big T, you can use the insert type in a turret type tool post. I did that for a long time untill I got my QCTP.

                    Go back and read my post above your last post.
                    You are right, I was thinking about the blade style with the insert on either end.

                    I part tight to the chuck, and use lots of oil. Tried water soluable oil solution as well, spraying right in the groove.
                    Turning at 550 rpm the finish is smoother, just a little more tense!!

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                    • #11
                      I used to fight parting till I just took the time to grind a 1/2 HSS square bit and grind most the right side off for .600" long or so and leave an 1/8" of the left edge then I could also add more clearance to the sides so it wont bind.

                      I will see if I can video what a small parting tool I make looks like.

                      BRB

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                      • #12
                        Here is a video of one made from 1/4" HSS, its better then them blades that bind up. Use a bigger peice for bigger work is all.

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                        • #13
                          Maybe I missed it, but I didn't see any discussion of speeds. I turn my lathe down to the lowest (60 rpm, regardless of workpiece diameter) and advance the tool with my left hand while keeping the the tip flooded in oil with my right. Don't stop and let the tool rub and harden the work. If you need to pause the operation for some reason, back the tool out a little so it doesn't contact the work.

                          I use a HSS tool that is 1/8 x 5/8 or so, with a wider top, and little relief under the nose of the tool.

                          I had pure misery before going to low speed.
                          Lynn S.

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                          • #14
                            I found most of my parting problems disappeared on both an old 9 x 18 conehead with a bit of wear, and a 13 x 40 import, when I switched to a sprung tool holder which uses tapered 3/32 (at the top) HSS blades. Works well on mild steel with a small back rake and set right on center height.

                            franco

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                            • #15
                              Big T, the double end insert blade is what I am talking about. They mount in a holder that mounts in any turret tool post or QCTP holder. The QCTP kit comes with a parting tool holder for the HSS blades and I have blades for it but don't use it.
                              It's only ink and paper

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