UHMW lathe parting
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  1. #1
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    Default UHMW lathe parting

    UHMW (Ultra high molecular weight Polyethelene) is giving me a bad part off. I've tried many different speeds and feed combinations, but cannot clean up the part off. I have to make 3000 more and its just gonna be a pain removing that as a secondary operation. If anybody has any type of suggestion for the parting off that would be greatly appreciated. Also, if you have a suggestion on how to remove of the excess parting material shown in picture efficiently please let me know (already made 2500). Thank you

    img_2267-1-.jpgimg_2266-1-.jpg

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    Are you using a partoff tool with an angle, or is it straight? An angled partoff blade will reduce the material left on the part, and a small radius on the tip will leave a nice finish.

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    You want a dead-sharp parting tool, on or a tiny bit below center. If you're using an insert tool, you may want to swap to a HSS or Cobalt blade, very carefully sharpened with clearance on sides and relief angle.

    You might find that peck-parting will help prevent strings of chips building up. And yes, a small radius at the angled tip will give a better finish. Hone it in with a good slip (sharpening) stone, being careful to maintain rake angles (don't radius the wrong part of the tool!).

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    If nothing suggested here works for you, you could use a sharp single flute countersink to remove the extra flash. Could probably just hold the parts with your fingers and use a battery operated drill to turn it.
    Or mount the countersink in a drill press and just touch the parts to the countersink as it turns.
    Obviously try modifying your tool to avoid this secondary operation, but I've experienced the same thing and deburred them this way.

    (And still have ten fingers.....)

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    I will try this out. Thank you @Milland and @charlie gary

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    Yup. My current plan was going to use a drill press, but I didn't think about a a hand drill. Thank you.

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    Surprised nobody has recommended using an ID grooving tool and cutting a groove at parting z depth, then part into the groove. It has helped to eliminate this nonsense for me in the past. Need sharp inserts, hss or dead sharp carbide. And you will probably need to play with speeds/feeds a bit, but I'd be going down that route before dealing with those by hand myself.

    Sent from my SM-G955U using Tapatalk

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    For a quantity that big, I'd add a threading tool to the program that has enough reach to put a chamfer on the ass end of the hole. I'd also get a narrower (1/16") brazed carbide Micro 100 part-off tool and grind a huge positive hook at the front of it. The trick is to end the chamfer exactly at the end length of the part. When the part off tool does it's thing, there should be either be a very tiny ring that you can removed with your finger, or if you're lucky, no burr at all.

    As for the parts you've made already, get yourself one of those Noga deburring tools and grind/hone a blade until it's razor sharp. Makes deburring plastics a breeze.

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    If you have live tooling, just toss a slitting saw in place of the cut-off tool and drive on.

    It is a game changer!


    ------------------

    Think Snow Eh!
    Ox

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    Using a drill press or a hand held drill isn't going to work. The first part you try will grab and try and suck the tool in. You could do that with Delrin but not UHMW.

    As suggested, use a part off tool with an angle. Angled such that the forward edge of the angle is up against the part, so the part is parted off cleanly. Don't use any radius, other wise you will have the last remnants of the radius left on the parted side. And as suggested put a chamfer on the inside before parting off.

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    Quote Originally Posted by triumph406 View Post
    Using a drill press or a hand held drill isn't going to work. The first part you try will grab and try and suck the tool in. You could do that with Delrin but not UHMW.
    Do lots of UHMW. Never had this happen

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    Quote Originally Posted by alphonso View Post
    Do lots of UHMW. Never had this happen
    It's happened to me, maybe I was doing it wrong. wouldn't be the first time

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    Quote Originally Posted by triumph406 View Post
    Using a drill press or a hand held drill isn't going to work. The first part you try will grab and try and suck the tool in. You could do that with Delrin but not UHMW.

    As suggested, use a part off tool with an angle. Angled such that the forward edge of the angle is up against the part, so the part is parted off cleanly. Don't use any radius, other wise you will have the last remnants of the radius left on the parted side. And as suggested put a chamfer on the inside before parting off.
    I've tried the dead sharp tool in plastic, and the finish was not good. I put a .003" radius on it and the resulting finish was smooth and shiny without a noticeable burr. If he also incorporates the threading tool to chamfer the end of the part before parting off, he stands a really good chance of getting a completed part that requires no deburr work at all.


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