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    Re: Backlash
    From: Bruce Stark
    Date: 2005 Nov 21, 10:12 EST

    You wrote:

    I think there must be lateral, as well forward and backward thrust when the
    worm gear is turned, so even in an upright position it will occur.

    I understand what you  are saying, but think the weight of the index might help trigger the effect if the sextant was horizontal.

    Assuming the gears are properly cut and aligned, it puzzles me that there's enough resistance to cause that cocking, or twisting, effect you've mentioned in one of your posts. Seems to me the only resistance worth mentioning should be in the friction of the gears themselves. And if the gears are well brushed out and have a light smear of Nye clock oil on them, that shouldn't be much.

    Possibly there's something wrong in the way the shaft of the worm gear is fixed in the index. The least bit of fore-and-aft play would cause a considerable backlash. My Tamaya has a stiff flat spring pushing on the end of the worm screw to controle this, and I think I can see a coil spring in the barrel of the of the SNO-T.

    Your and Alex's postings have caused me to notice the way these sextants are put together. But the business of index error changing with telescope focus is beyond me. When the weather allows I may give it a try.


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