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  • Coloured Plastics

    I'd like to machine up various coloured knobs for the controls on a tractor. Preferably bright colours. What plastic is suitable for this? It needs to be machineable / threadable, hard enough but shatterproof and available in 35mm or so round bar stock. Resistance to diesel would be nice - the stuff seems to get everywhere!

    Thanks,

    Ian
    All of the gear, no idea...

  • #2
    High Density Polyethylene, (HDPE,) might work. It machines easily and comes in white, black, blue, orange, red, and green, (that I know of.) It is unaffected by most solvents. Where to get it? Try a plastics supplier. Around here, someone is packaging slab offcuts in 3 lb bags, which is handy for little jobs like slippery feet on heavy machines. These dont move on a concrete floor, but CAN be moved with a bit of effort. I assume round stock would be available.
    Duffy, Gatineau, Quebec

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    • #3
      Ultra High Molecular Weight (UHMW) polyethylene comes in many colors.

      ebay (US) has Yellow, Pink, Blue and Orange available now from one seller, might make up a box with your preference of colors.
      Search "UHMW"

      It machines just fine, is resistant to many fluids, should be good for your application.

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      • #4
        That isn't a very demanding application except for one thing. They need to be UV resistant. For that the best is a UV stabilized HDPE product. Check with a marine chandler or outfitter for a source.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          delrin would work. You can get drops off ebay in different colors.

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          • #6
            I just saw a posting on PM from someone who uses old billiard/pool/snooker balls for this. Apparently they machine nicely, and at least some are solid color all the way through. The person in question is from the UK, where I guess old snooker balls turn up more frequently than here in the states, but I wonder if old bowling balls would work.

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            • #7
              Try pen turning supplier:

              http://www.pennstateind.com/store/pen-blanks.html

              diameter might be a problem, but the variety is good.
              Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
              ~Practitioner of the Electromechanical Arts~

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              • #8
                bruto, old bowling balls are not a good choice. I had to machine a ¾" groove about `1 ¾" deep in a bowling ball for a friend. The inside is some sort of black stuff mixed with cork. It cuts dirtier than cast iron and is extremely abrasive.1 pass to full depth would put a very noticeable radius on a HSS tool, had to sharpen every pass. A grinding wheel is only slightly less abrasive. Also, the material does not tend to produce a nice finish, even in the 5 seconds the bit stays sharp.


                Ed

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                • #9
                  Originally posted by The Doctor
                  bruto, old bowling balls are not a good choice.
                  Ed
                  I was not going to stick my nose in a thread about plastic , but I just can't help myself.
                  WHY WOULD ANYBODY IN THEIR RIGHT MIND USE BOWLING BALLS FOR TRACTOR KNOBS? .

                  STEVE

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                  • #10
                    Thnaks all,

                    Great replies as usual.

                    Evan, the tractor will be spending most of its time under covers or indoors when not in use, so UV resistance shouldn't be a problem (the driver is less UV-resistant than most plastics).

                    Good tip on the UHMW - the guy has some interesting colours; I'll see if he can put a custom pack together.

                    Snooker balls; mmm...

                    Ian
                    All of the gear, no idea...

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                    • #11
                      Originally posted by doctor demo
                      but I just can't help myself.
                      WHY WOULD ANYBODY IN THEIR RIGHT MIND USE BOWLING BALLS FOR TRACTOR KNOBS? .

                      STEVE
                      I think he meant to cut a bowling ball up and turn knobs from the smaller bits.

                      bollie7

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                      • #12
                        I had to machine a ¾" groove about `1 ¾" deep in a bowling ball for a friend.
                        Now I want to know why? And how?
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Originally posted by bollie7
                          I think he meant to cut a bowling ball up and turn knobs from the smaller bits.

                          bollie7
                          Yes, that was the idea. They would be a little ungainly otherwise.

                          Thanks to the Doctor for the warning. I thought some might be solid plastic.

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