Boring tool for poly bushings??

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  • torker
    Senior Member
    • Dec 2003
    • 6048

    Boring tool for poly bushings??

    What do you guys use for this? I wasn't stupid enough to try to use my carbide boring tools and have tried a homemade HSS cutter made from an end mill but I'm not sure what profile I should grind on it.
    The one I have cuts well but it seems to hook into the poly and it is all too easy to cut oversize.
    Any suggestions?
    Thanks!
    Russ
    I have tools I don't even know I own...
  • balddave
    Member
    • Sep 2004
    • 39

    #2
    I know that a dull drill bit won't grab into the softer materials like brass and plastics ect. So maybe try dulling or just putting a larger radius on you current bit.

    Comment

    • darryl
      Senior Member
      • Jan 2003
      • 14400

      #3
      I modified a standard drill bit by stoning off a very short portion of the lips to a zero rake- seemed to improve things in some plastics. I don't know if there's an endmill with a zero rake, but that could be an answer. I have a reamer with straight flutes and that's not too grabby in poly. It helps to have lots of flutes so it has less tendency to wander sideways. Just my experience, I'll defer to others with more knowledge of machining plastics.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

      Comment

      • mochinist
        Senior Member
        • Oct 2003
        • 2425

        #4
        Well I think I made only one thing out of metal this week, other than that everything I worked with was delrin, uhmw, and nylon(for the record I hate uhmw and nylon, crappy stuff ). For all of those I like a nice sharp piece of hss with little or no radius on the tip for lathe work and I just use regular endmills and drills for it on the mill. For your boring bar you dont want a radius on the tip, if there is a radius it just rubs and leaves a ****ty finish. I had to bore a bunch of nylon bushing's yesterday on the lathe, instead of using a hss steel boring bar, I just used one of mine that takes carbide insert. I took an old insert that was in the used carbide box, and I sharpened the cutting edge and got rid of the nose radius, it left a nice smooth finish, which can sometime be hard to get in nylon. A little water based cooling oil seems to help also.

        Comment

        • Davis In SC
          Member
          • Jul 2005
          • 64

          #5
          Poly is a big word... Actually, all plastics are POLYmers. I assume you are cutting UHMW ( Ultra High Molecular Weight Polyethylene) I suggest a rigid boring bar (HSS in OK) very sharp, with lots of back rake. Also, try taking a minimum of .010 dia. on the finish cut. Smaller cuts tend to push the plastic away from the cutter, you keep making very small cuts, then whamo...tool bites in & you are way oversize... HTH

          Comment

          • Evan
            Senior Member
            • May 2003
            • 41977

            #6
            I do lots of plastics including ABS, Nylon and Teflon. I use the same tools I use for aluminum, lots of rake and really sharp with good speed. For boring an initial hole I found a wood spade bit works well. It has lots of room for chips and doesn't grab.

            This hole in nylatron was made with a spade bit.

            Free software for calculating bolt circles and similar: Click Here

            Comment

            • torker
              Senior Member
              • Dec 2003
              • 6048

              #7
              Sorry...I should have mentioned...this is polyurethene bushing material (A60 Durometer)
              I see one thing I was doing wrong. Taking too light of a cut for the final pass. I haven't worked with this stuff enough to be sure but these bushings are expensive and i don't want to ruin any.
              Hmmm, I'm also getting a rough finish...maybe a sharper tool,more backrake and higher speed like has been mentioned.
              I find with UHMW if I go too fast It starts to melt.
              Thanks!
              Russ
              I have tools I don't even know I own...

              Comment

              • Evan
                Senior Member
                • May 2003
                • 41977

                #8
                The sharper the better to reduce friction. That's what makes it melt more than the speed. More rake stops it from digging as it slices it like a knife.
                Free software for calculating bolt circles and similar: Click Here

                Comment

                • torker
                  Senior Member
                  • Dec 2003
                  • 6048

                  #9
                  Thanks Evan...makes sense! Guess I haven't taken the time to really sharpen the cutter. Seems with too much backrake it digs in and will pull the bushing out of the chuck. This is pretty soft stuff and I can't tighten it too much without it deforming.
                  I have tools I don't even know I own...

                  Comment

                  • jburstein
                    Senior Member
                    • Sep 2004
                    • 179

                    #10
                    If you have some cold spray (either from the first aid kit, or the stuff used as "chip coolant"), spray it into your hole right before boring. That works pretty well on most plastics, although you should be aware it can shrink them, and change your final size. If the wall around your bore is thick enough then you shouldn't have much of an issue with that, though. I use it for roughing passes, because it keeps the plastic from melting.

                    -Justin

                    Comment

                    • Evan
                      Senior Member
                      • May 2003
                      • 41977

                      #11
                      Russ,

                      I make all sorts of stuff out of black rigid PVC pipe (telescope dew caps, spotting scopes etc). It is very difficult to hold in the chuck. Depending on what I am doing I either make a wood or plastic plug to fit inside or a collet from aluminum for the outside. In your case since these items are expensive I would make an OD collet to hold them in the chuck. Digging in is certain if the material is soft and you can't hold it securely. It will shift under cutting load.
                      Free software for calculating bolt circles and similar: Click Here

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