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Change gears for 9mm lead, three-start thread?

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  • #31
    Thanks Baz. I do have two 120's, yes. They won't fit in the A position though as anything larger than 60 will hit the spacer on the drive gear. I've already slimmed the spacer down but unless I shorten the drive gear shaft down (and lose the option to reverse the leadscrew) I couldn't get anything larger on.

    This is the gears laid out as per the 60/30, 90/40 suggestion but with the 90 gear removed for visibility. The B/C shaft is set in the right location for meshing the 90 tooth C with the 40 tooth D. You can see that the B just won't mesh with the A because the end of the banjo hits the gear the sits behind A:

    With the A gear removed this is easier to see:

    Swinging the banjo all the way round doesn't help any of these combinations either:

    From the front, you can see what I was thinging about making a banjo that sits further back. It wouldn't get me much more clearance but make it just a bit shorter and it might clear the (fixed, static) shaft that carries the A gear. With a 100 tooth gear on the banjo meshed with a 100 tooth gear (largest combination on the chart) there's about 10 to 15 mm extra length of banjo than there needs to be.

    I could add an idler gear by mounting a plate to the two SHCS (rather than drilling randomly) but it dawned on me that there would need to be two idlers or it would reverse the direction.

    And no, I didn't think about being able to open the door when I mounted those brass hooks for hanging chuck keys on.


    • #32
      Come up with a new crazy idea. Should just about be able to shove an idler gear on the same banjo and run the A gear off the other spindle to compensate for the direction change. Seems to fit for 60-40/90-50-30 which should give me 9mm pitch. The extra spindle, t-nut, sleeve and key are all available as spares too so I might give that a try.