Announcement

Collapse
No announcement yet.

Gear Material Help

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Gear Material Help

    I had a crash today with my Sheldon lathe and it ate the teeth off the gear in the reverser/lead screw drive assy. The gear was phenolic so it sheared the teeth without further damage. I called National Acme ( dealer for Sheldon parts) and was told the gear was not in stock but was available. I asked how much and was told $595 and it would take 4 to 6 weeks. When I regained conciuosness I said thank you , have a nice day. He was insulted that I thought that was a rediculous price.

    I ordered an involute gear cutter from MSC and will make my own. I now need to decide on a material that will have properties similar to the original phenolic. If this happens again I want the gear to shear rather than tear up the whole gear train. If using a plastic material of some kind I will press a brass bushing in the center. The gear is engaged any time the lead screw is turning so wear is a factor.

    What suggestions to you all have?

  • #2
    NYLATRON
    http://www.gcip.co.uk/EP/materials/nylatron.htm

    We have used it for gears that run the governers for hydroelectic turbines at the dams here in the northwest. its good stuff.
    Last edited by tattoomike68; 02-25-2008, 03:21 PM.

    Comment


    • #3
      That was probably a filled phenolic which is often used like that. I note that McMaster Carr has it, maybe listed as or under Garolite. Micarta is another brand name.
      .
      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

      Comment


      • #4
        You could make it out of phenolic.

        Grade XX Garolite is a phenolic which might be pretty close to what your gear was made from. McMaster-Carr sells it in big sheets, or in nice small gear-sized pieces.
        __________
        Oops, beat to it.

        Comment


        • #5
          Probably made from tufnol, this was (later) standard practice on tumbler reverse gears on Myfords.
          Info here, look under>techical>tufnol gears : http://www.tufnol.com/tufnol/default.asp

          Incidentally Sir John makes and sells these as replacement parts in batches.

          Peter

          Comment


          • #6
            Tufnol which is just a trade name is used for these sacrificial gears just as Peter has said.

            You can also buy a steel gear and bush it with another steel bush for a rotating fit and drill a 3/32" hole part way in both and fit a bit of brazing rod in.

            Then if you get a crash it just shears the brass pin, new pin and you are back running with virtually no down time.

            .
            .

            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



            Comment


            • #7
              Originally posted by John Stevenson
              Tufnol which is just a trade name is used for these sacrificial gears just as Peter has said.

              You can also buy a steel gear and bush it with another steel bush for a rotating fit and drill a 3/32" hole part way in both and fit a bit of brazing rod in.

              Then if you get a crash it just shears the brass pin, new pin and you are back running with virtually no down time.

              .
              Brilliant!

              That's what I'd be doing were it my baby.

              Best,

              BW
              ---------------------------------------------------

              http://www.cnccookbook.com/index.htm
              Try G-Wizard Machinist's Calculator for free:
              http://www.cnccookbook.com/CCGWizard.html

              Comment


              • #8
                Yeah the shear pin idea would be a good one except its not driven from it's center it's just basicaly an idler gear between two driven gears and simply rides on a bushing on a smooth shaft.

                Comment


                • #9
                  Originally posted by John Stevenson
                  Tufnol which is just a trade name is used for these sacrificial gears just as Peter has said.

                  You can also buy a steel gear and bush it with another steel bush for a rotating fit and drill a 3/32" hole part way in both and fit a bit of brazing rod in.

                  Then if you get a crash it just shears the brass pin, new pin and you are back running with virtually no down time.

                  .
                  I'm a little dense. Is the result like a 1/2 round keyway in the gear and bush with the 3/32" rod as a key?

                  Regards to Robin, Maid Marion, and the rest of the band in the forest.

                  Comment


                  • #10
                    Originally posted by GKman
                    I'm a little dense. Is the result like a 1/2 round keyway in the gear and bush with the 3/32" rod as a key?

                    Regards to Robin, Maid Marion, and the rest of the band in the forest.
                    No, I believe the pin is transverse like a roll pin to hold the bushing and the gear together rather than a shaft key configuration.
                    .
                    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                    Comment


                    • #11
                      Thanks for all the suggestions. I'm going to try nylatron as tattoomike68 sugested as I can get it locally and it machines well and is very reasonable in cost.

                      Comment


                      • #12
                        Nylatron is great stuff, but the reason phenolic/Tufnol/Garolite/Micarta is used in lathe headstock gears is because it's one of the few materials that damps vibration (in the gear train) better than grey cast iron.
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                        Comment


                        • #13
                          I would want to know the comparative impact resistance of the original gear compared to Nylatron or acetal. Acetal and Nylatron both have impact resistance equal to or greater than a steel gear of the same dimensions. It is likely that the "fuse" properties of the phenolic gear will be lost by using either plastic.
                          Free software for calculating bolt circles and similar: Click Here

                          Comment


                          • #14
                            But does the plastic have a shear strength greater than steel because that's what happens when these go.
                            One stops, one carries on and it's a guillotine effect.

                            .?

                            .
                            .

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                            Comment


                            • #15
                              Originally posted by Evan
                              I would want to know the comparative impact resistance of the original gear compared to Nylatron or acetal. Acetal and Nylatron both have impact resistance equal to or greater than a steel gear of the same dimensions.
                              The impact strength may be better, but I bet the wear resistance (limiting PV and K ratings) is lower on Delrin or Nylatron than phenolic, due to the glass-filled content.

                              Heck, even on the Nylatron family, there's a 20x difference in wear resistance between the unfilled Nylon 6 (normal Nylon), Nylatron GSM (Molybdenum filled), and Nylatron NSM (some secret formula that Quadrant hasn't revealed).

                              Delrin K wear resistance (K rating) is far lower than Nylatron: 211 In-min/
                              Ft-Lbs-Hr, versus 83 for Nylatron GSM, and 8 for Nylatron NSM (which is equal the wear resistance of bronze, by the way...).

                              That means that a Delrin gear would wear about 3 times as fast as a Nylatron GSM gear, under the same pressure/velocity conditions.

                              Nylatron was specifically formulated for high wear gears, bushings, ...
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                              Comment

                              Working...
                              X