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How to separate the A gear on 9 x 20 Lathe

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  • How to separate the A gear on 9 x 20 Lathe

    I want to set up my Harbor Freight 9 x 20 lathe to do some screw thread cutting for the first time. I need to change the A and B gears to both be 30 T. The B gear was no problem. However, the A gear is a 28 T gear stacked on a 40 T gear on a keyed bushing. I need to swap out the 28 T gear for a 30 T gear. How do I separate them without damaging them? The 28 T / 40 T stack is on the left in the picture. The new 30 T gear is on the right. The stack is placed on the shaft in the back and held in place with the collar with a set screw.
    Click image for larger version

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  • #2
    my guess would be to press the central keyed bushing and small gear off the big gear with a press or some contraption in a bench vise, then press the keyed bushing out of the small gear. Reassemble by pressing the bushing into one of the new gears and then pressing the other one onto the shaft.

    If you need to make this change more frequently it might be worth buying a spare keyed bushing and larger gear so you can keep 2 compound gear assemblies to hand and swap them out when needed.

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    • #3
      Drill through the large gear partially into the smaller. Maybe 1/2 way between the bore and gear teeth root. Tap the holes through the large gear and use screws to separate.

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      • #4
        Press the keyed bushing through, that's what I did with mine.
        John b. SW Chicago burbs.

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        • #5
          If the keyed bushing goes all the way through, I'd think you could simply press that out and the gears would also separate. Since these gears are intended to be changed, I would also guess that the press fit is a very light one.
          "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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          • #6
            It is supposed to just come out easily. Not made to spec? You need to press it out.
            The shortest distance between two points is a circle of infinite diameter.

            Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

            Southwestern Ontario. Canada

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            • #7
              Spray some PB blaster on it and put a heat gun on the gear?

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              • #8
                No need to drill anything! I let mine soak in WD-40 for a half hour or so to loosen the goo it was packed in, then wiggled and worked them away from each other by hand. Once apart, I thoroughly cleaned and lightly oiled them. Now they come apart and go back together tightly but smoothly.

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                • #9
                  Thanks for the quick responses everyone! I'll give the WD-40 a try followed by pressing out if necessary. Long term, I may set up stacks of the most frequently used combinations.

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                  • #10
                    arbor press

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                    • #11
                      No need for pressing. A simple drift will do it.
                      'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                      • #12
                        Follow up: In my case WD-40 wasn't sufficient. Pressed the bushing out - touched up all of the edges with a file to debur - still had to press the bushing back into the gear stack. All is well that ends well and this ended perfectly!

                        Thanks for all the help available on this forum!!!

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                        • #13
                          With tight push fits where you know it is meant to come apart just put on some music with a good rythm. Pick up the gear pair holding the larger gear at the edge between finger and thumb with the small gear downwards. Then tap the far side of the large gear down on something solid like a corner of your vice in time to the music. Tappety-tap for few minutes the time will soon pass as you beat the rythm of the music and with each little tap the weight of the small gear will gradually seperate it from the larger one with the bush making its own mind whether it will join it or not.

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                          • #14
                            Bearing splitter and pry bar or wedges.

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