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  1. #31
    Quote Originally Posted by johnsattuk View Post
    They come in various sizes, 11 is quite a small one, do you know shaft sizes
    I think it is 6mm in, 12mm out.

  2. #32
    Quote Originally Posted by magicniner View Post
    It could, but I've been making parts with my "rubber band" for a couple of years, how's it going with your "Doorstop" ?
    Well enough:

    https://www.youtube.com/watch?v=lVuBEEceWJ4
    http://www.mycncuk.com/threads/3341-...illing-machine
    http://www.mycncuk.com/threads/11220...-as-a-4th-Axis

    Unfortunately I ran the stepper motor on the rotary table into my milling machine column (wasn't looking) last year and bent the worm gear, so I do have another doorstop! I'm now wondering if these are better than the price suggests:

    http://www.ebay.co.uk/itm/Precision-...sAAOSwZ4dZHZkC

    The problem with the direct belt drive method is the stiffness of the belt is quite poor compared to a harmonic or worm drive. Of course, it can be useful but that depends somewhat on the diameter of the material, your accuracy requirement and other factors. If the rotary table above is any good - i.e. "most" of the backlash can be adjusted out, then that plus a 1Nm stepper motor seems like an attractive option.

  3. #33
    Quote Originally Posted by magicniner View Post
    Surely you'll be using Anti-Backlash gears from HPC Gears as it would be a strange choice to add backlash in the primary drive (regardless of how small an error this would introduce) of a system designed specifically to avoid backlash?
    Wow, it almost designs itself.

  4. #34
    Robin if it's like mine in size 11, then it's probably 6mm in, 10mm out.

    And Jonathan, I also have a size 50 monster that I use on a crane rig, weighs a bit that one:)

    Edward

  5. #35
    Quote Originally Posted by Robin Hewitt View Post
    Wow, it almost designs itself.
    That's extremely fortuitous then ;-)
    You think that's too expensive? You're not a Model Engineer are you? :D

  6. #36
    I just took that harmonic drive apart, one screw head decided to snap off, one had to be drilled off.

    Much as expected, only remarkable thing is how fine the gear pitch is.

    These gears are about 28mm diameter...

    Click image for larger version. 

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    Last edited by Robin Hewitt; 28-08-2017 at 11:18 AM.

  7. #37
    Not just the fine pitch but also the fact that they are flexible to mesh and I am not totally sure about the inner workings, but I think they have one more tooth than the gears they mesh with, or vice versa. Incredible concept and I guess very difficult to machine such precision.

    Edward

  8. #38
    Quote Originally Posted by Edward View Post
    Not just the fine pitch but also the fact that they are flexible to mesh and I am not totally sure about the inner workings, but I think they have one more tooth than the gears they mesh with, or vice versa. Incredible concept and I guess very difficult to machine such precision.

    Edward
    Need 2 teeth difference and because of the fine pitch, need a bit of care when reasemmbling as it is easy to be one tooth out, do not force.

  9. #39
    I have to get those headless screws out before I can reassemble.
    M2.5 and darned close to the bendy cog. I don't have anything suitable to grab them with.
    Any ideas?

  10. #40
    Have you tried two or three nuts locked together perhaps with heavy duty locktite retainer as well
    Last edited by johnsattuk; 28-08-2017 at 12:22 PM. Reason: spelling

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