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  1. #16
    Join Date
    Aug 2011
    Location
    Melbourne
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    4,779

    Default

    Some clearance adjustment between worm and wheel can be used to find a sweet spot but only to a point. A properly set up gear system has a pre-determined spacing and if they are moved, it starts to affect the smooth operation of the gear movement. (For want of a better term) If they are too close then their movement becomes notchy.

    Some worm and gear systems have the ability to adjust clearance to do exactly what you suggest (such as dividing heads and rotary tables) but it's more to reduce backlash caused by wear.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  2. #17
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
    Posts
    1,075

    Default

    Technically, yes you could do that but depending on how accurately both gears are cut (and whether the worm is cut to full size or slightly under the theory OD) you may end up bottoming out on the OD of the worm before the teeth fully contact on both sides.

  3. #18
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,540

    Default

    Quote Originally Posted by simonl View Post
    Some clearance adjustment between worm and wheel can be used to find a sweet spot but only to a point. A properly set up gear system has a pre-determined spacing and if they are moved, it starts to affect the smooth operation of the gear movement. (For want of a better term) If they are too close then their movement becomes notchy.
    If the mesh is notchy, then the movement has gone too far. In a commercial box the shafts are fixed so you can't but for a special application where zero backlash is critical, there would be a way. As you point out, rotary tables and dividing heads do it, and I can think of another method that would probably work too. It helps that this application is slow speed so less vibration that whill shake things out of adjustment.

    Quote Originally Posted by elanjacobs View Post
    ... depending on how accurately both gears are cut (and whether the worm is cut to full size or slightly under the theory OD) you may end up bottoming out on the OD of the worm before the teeth fully contact on both sides.
    However, normal gear cutters are cut with an allowance to make sure the teeth do not bottom out ('D+f' is bigger than twice the distance between the OD and the PCD). A proper wormgear cutter should have a similar allowance built in to provide clearance when the wormgear is mated with a nominal size worm. If the worm is oversize, then there may be problems...

    Michael

    Michael

  4. #19
    Join Date
    Apr 2015
    Location
    Tungkillo, South Australia
    Age
    87
    Posts
    74

    Default

    Quote Originally Posted by simonl View Post
    I see. So why do you have to do a meridian flip during an exposure?

    Nice pic BTW.

    Simon
    Obviously not during an exposure but there are usually many exposures taken to get sufficient data for a good image. A meridian flip will be taken between them when required. My image used approx 160 exposures of 900 or 1200 seconds each over a few months.

    Charles

  5. #20
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default Look for Neil Wyatt posts

    The editor of the Model Engineer Workshop magazine is a keen astronomer who makes his own gear and does astronomy photographs. He has made comments that you might find helpful in various posts.

    https://www.model-engineer.co.uk/for...?th=112201&p=1

    Other posts in those forums might also be helpful.

    Bill

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