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Lathe Turning of Rubber Seals ????

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  • Lathe Turning of Rubber Seals ????

    I'm in a bit of a bind here, I have some old hydraulic rams that are in need of new coupler seals. You cant buy the seals individually any more, you have to buy the whole coupler, too expensive. I know that there are places that custom make seals which are turned on a lathe, If your turning rubber round stock, say Buna-N or EPDM rubber I would imagine that the cord stock is held in the lathe by a collet for minumum deformaty. What I'm wondering is if anyone knows if there is any special tooling used to cut, turn face or drill soft material such as what I mentioned. They would have to be very sharp tools. These guys that do this stuff seem to keep it a secret. I think any rubber around 80 durometer should be machineable with proper tooling.


  • #2
    I think the big secret is to put it in the freezer over night. On the coldest setting you have. Plan your work and work quickly.


    • #3
      Freeze it

      Freeze it just before use and if needs be at various stages of machining.

      Lathe tools need to have a cross-section like a very fine, small - and very well polished/honed finish and very sharp. Use plenty of coolant (water only is preferred). Take is slowly - very. For roughing, a cutting edge like a parting tool with a "chip breaker" works well too (tool is like the old-fashioned HSS parting-off tool).

      Make sure the tool actually "cuts" and does not "rub".

      Try a series of "test runs" first to get the "feel" of/for it.

      Machine rubber the same way.

      If it softens or gets any more than "cold" it will "grab".

      Coarse high-speed "burrs" work well when the job is cold as well.



      • #4
        The biggest factor determining machineablility will be the durometer of the material.

        I've done a fair bit of urethane(probably about the same as rubber) in the 90A and harder durometer. That's a bit harder than the sole of a sports shoe. Softer than that and you won't have much luck, in my experience.

        We use high positive carbide insert tooling because that's the sharpest thing we could find.

        Freezing overnight does help, but you have to work fast.

        Grinding can sometimes be a better method.


        • #5
          Would it be possible to make a mold and cast them from Chicago latex?


          • #6
            I don't think freezing the piece will do much good since the flexability of the material won't change much at 25 degrees. Maybe at -300 degrees if you can get some liquid nitrogen but by the time you ran from the refrige to the machine the part would be warm.



            • #7
              You can stink the shop up grinding it with a Dremel.
              I just need one more tool,just one!


              • #8
                +1 for freezing and +1 for grinding. Grinding with a stone works so much better than cutting it with a tool.
                This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                Plastic Operators Dot Com


                • #9
                  Burrs etc

                  Freezing it will work - to a degree (sorry) - and its better than shop or machine temperature.

                  I forgot to add/say that the water "coolant" should be "lubricant" - with just a small dash/drops of kitchen-sink concentrated detergent. Too little and it loses its lubricity and too much may cause the cutter to "slip/rub".

                  It does not need to be in the main coolant tank/system - just apply with a brush from a tin which is in cold/chilled water.

                  These burrs work well too - but will heat the job if you are not careful to keep them and the job cold:


                  With a 1/4" shank, they require a die-grinder or similar with a 1/4" collet and lots of speed and "grunt" - like this:







                  • #10
                    90 durometer rubber packer elements, as used in BP's infamous GOM well are often reduced in OD, so's to pass through out of gage wellbores. ie 9 inch reduced to 8 inch OD, etc.

                    Elements are fitted snug/solid onto a mandrel, turned slowly and shaved using a tool which looks for all the world like a woodturner's half moon tool, a razor sharp, curved cutting edge with all kinds of clearance. 2 inch dia. tubing was often 'sharpened' and held in a fabrication at such an angle to produce the shaving/shearing action.



                    • #11
                      Could you punch them out of sheet stock with a hollow punch? If the OD was a little too big or they needed to be an exact OD, you could sandwich them between 2 pieces of steel of a slightly smaller OD and turn or grind to size.
                      Kansas City area


                      • #12
                        Rubber grinds quite well, but it does stink up the place and makes a mess. Other than that, you can use a fine stone and get a pretty decent finish. I think the trick with rubber is to have the cutting edges skimming it at a very high speed, so the inertia of the rubber molecules keeps it in place as each cutting edge removes the smallest bit of material. That's why grinding works so well, and no freezing required. By the way, urethane isn't likely to get much harder unless it's very cold- and how are you going to keep it that cold over the time it takes to mount it and cut it- . Better I think to grind, have the stone fresh (not loaded up with anything) and use a high SFM.

                        Most any time I grind on something like an O-ring, I'll turn a fixture to mount it on. Sometimes it's a friction fit, other times I'll fit it onto a boss then add a disc to clamp against the side of it. I keep a stone sharpening tool handy to touch up the stone, and that makes grinding easier and less likely to distort the rubber during the process.

                        If you do want to freeze it before turning, consider making some kind of mount that you can quickly attach to the spindle somehow, then freeze the mount with the rubber piece on it. The cool will last longer between turnings, but of course it will take longer to re-cool.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                        • #13
                          Would it be possible to use a razor blade to do the cutting in the lathe? A hobby razor would fit nicelly in a boring bar holder.



                          • #14
                            I once tried turning rubber from a dog chew toy on my lathe. When I left, I was still trying to clean the "GUM Powder" off my lathe...
                            Does not turn very well. If it is soft, it will tear more than anything.


                            • #15
                              Do you have the size of these?