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Pratt Burnerd Three Jaw Chuck Cleaning

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  • Pratt Burnerd Three Jaw Chuck Cleaning

    I am trying to save the three jaw chuck that came on my Boxford lathe. A few days ago the jaws would not move. After a soak in the solvent tank for three days the movement is better, but stiff. The outside I'm able to clean up pretty well, but the inside is bad. I am able to see a large amount of crud (rust, dirt, chips) down inside on the scroll and in the slots. How would I go about removing the small plate from the back of the chuck to get access to the insides of the chuck? I did remove the three Allen screws on the back and the plate appears to be stuck to the body with surface rust. I tried to tap lightly with a brass hammer and nothing moved and the rust around the edge of the plate is pretty solid, so I put the screws back in and snapped these pictures.

  • #2
    Pull those three screws, keep soaking. Wind the jaws so they come out and tap around the scroll. It'll pop that back plate off.



    • #3

      I have the exact same chuck. Just takes a bit more persuasion


      • #4
        As it has already soaked for some time,While it is wet remove the jaws and the Scroll drivers don't know if that is the correct terminology, remove the back plate screws clean the case back plate joint and light oil CRC if you have an anvil or a big block of steel place a piece of timber on top to stop burring hold the chuck with the jaw slots uppermost and dump the chuck down on the timber the weight of the scroll and back plate will move the back plate flush with the back of the chuck case don't put a punch through the jaw slots you cold damage the scroll


        • #5
          how about taking those three bolts out

          and making some sort of a tool that has three studs that go into the holes ..but not the threads.

          this tool would be similar to a c-spanner ..but with three prongs.

          the rotation would help free it.

          failing that, try heat the outer chuck.

          another method of tapping something without hopefully causing damage an air chisel ..modified with a blunt and shaped end..then start chiselling with it at low pressure ..

          all the best.markj
          Last edited by aboard_epsilon; 06-21-2012, 07:36 PM.


          • #6
            Originally posted by murph64
            Pull those three screws, keep soaking. Wind the jaws so they come out and tap around the scroll. It'll pop that back plate off.

            Not sure what size the OP's chuck is, but I have 2 PB 12" 3-jaws and have done exactly as murph64 says.

            Remove all parts that you can: jaws, 6 screws from the back, pull out the scroll drivers/pinions/whatever they're called, let 'er soak. tap down through the jaw slots on the scroll. Keep in mind that the back cover and scroll on my PB chucks are very snug. It takes a lot of light taps around and around to get the chucks apart!



            • #7
              Thank you for the tips. I was able to break it free by twisting with a pin wrench and once it was free it almost fell out by itself. Then after I removed the pinion gears, the scroll was lightly tapped out. Its all soaking again in the solvent. I will let it set there for a few days then try my hand at removing the rust and goop from the inside surfaces.