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Question about plastic gears

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  • Question about plastic gears

    I'm working on restoring a Inch/Metric compound lathe dial on a 1983s Monarch 10EE.

    Inside is a spur gear that drives the planetary gear on both the Inch and metric reading dials.

    The teeth on the each end of the spur are stripped where they mesh with the planetary gears.

    The spur gear has 28T,56R .535 dia., and is .746 long, with a 1/4 hole and is made of a plastic or nylon.

    The planetary gear with Inch marking has 127T -56R ?.(R or P) Both gears made of steel.
    The planetary gear with Metric marking has 125T -56R.

    I need to make or find a new spur gear and wonder if it would be better if the spur gear should be made of bronze or oil impregnated bronze.

    Thank for your help.

    Last edited by Hal; 01-03-2016, 10:15 AM.

  • #2
    Is the stripped gear the original gear? And it is made of plastic? If so, I'd use plastic. Monarch isn't known for cutting corners, so perhaps they made that gear to wear out, preserving the other gears?


    • #3
      Yes Tony I think the gear is original.

      I'm not sure what the gear is made out of a plastic or nylon.

      The teeth are missing in just one spot on each end of the spur gear.

      I dial shows a little light rust and I think the teeth were striped when the dial was forced.



      • #4
        Buy a replacement, or make one out of Delrin.


        • #5
          Many gears are made out of Grade Linen Phenolic. Is it a light gold color and if you look at it under a magnifying class have a fabric look? If it is, that'd Phenolic. You could contact Twin City Gear in Blaine MN and they can cut you a new one. It would cost less if you cut the blank. Be sure to wear a eye goggles and respirator mask when cutting it though.

          1551 99th Ln NE, Blaine, MN 55449 Phone763) 780-9780


          • #6
            Having a sacrificial gear in the train has saved a lot of damage, the broken teeth bits are too soft to cause damage elsewhere. The lathe I use has all metal gearing, but uses a shear pin 1/16" dia in the middle to save the gear train from damage during a pile up.


            • #7
              I had a similar issue with the 127 /125 transposing gears on my Okuma.


              Coolant had got in and seized up the metric side , so the previous owners had just taken out the 13T spur gear and threw it presumably.
              I found a cheapish 48dp 14.5deg pa 135-r no1 cutter and remade it in brass (the 127/125 are steel). Took a couple of goes as I went a bit to deep on the first..but the second attempt runs nicely.
              I rang an Okuma supplier and , if the cost is anything to go by , the original must have been hewn from billet gold by virgins.



              • #8
                Where do you find a virgin in Grimsby ?

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


                • #9
                  Originally posted by John Stevenson View Post
                  Where do you find a virgin in Grimsby ?
                  That's why one doesn't skimp when investing in one's tourist industry.


                  • #10
                    I didn't used to be a virgin but I am now, but I live in the N/east of England,




                    • #11

                      I don't see any fabric in the gear. It a off white, maybe a nylon.