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  1. #1
    abrocket's Avatar
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    Default scope weight stops mount - help



    Ok, its not as bad as all that. Here's what's happened so far:

    Picked up a scope and goto mount cheap. it's a 4.5" newton with alt/az motor mount. (celestron nexstar 114) it's a side mount with a c-clamp for the scope.

    When i first got it, the AZ motor was intermittent and not working great. i found out you could just buy these directly from celestron. this seems to be a few years old, so I just bought a new one ($16).

    the electronics on the new motor weren't the same, so I just put the old motor board on the new motor.

    while I was at it, I stripped down the mount, cleaned all the gears and regreased with super lube. including the motor gear train.

    now the mount works great -- runs great from the hand control --- until i put the scope on it.

    this is not a heavy scope. but the weight of the scope seems enough to stop the az from moving.

    no problem with the altitude motor.

    any ideas? what am i missing?

  2. #2
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    Default

    Hi welcome!

    can you post a few pictures? I think you got a good deal, what OTA telescope are you mounting on it?

    The 114 is not rated to carry much weight, but with a new motor and re-lube should be able to carry a bit properly balanced.

    Have you balanced the OTA on the mount carefully?
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  3. #3
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    Default

    If it is balanced, it shouldn't make any difference to the working - unless a bearing is allowing distortion of the mount assembly and interference is occurring.

    Certainly if it is not balanced, it will refuse!
    Also if the new motor and the old board are rated differently, it might restrict the current overmuch
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  4. #4
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    Default

    Grabbing at straws here.

    1. insufficient clearance between the drive gear and the large spur gear. Use a thin piece of paper when you adjust the clearance between the two gears. Simply put the paper between the gears then adjust.

    2. The azimuth axis bolt is a tad bit too tight.
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  5. #5
    abrocket's Avatar
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    Default

    So after taking this all apart and putting it back together for the nth time, a couple of things I've noticed.
    the base (the part that connects to the tripod) is keyed to the axle.
    but -- the axle turns freely within the mount side, AND .. the big spur gear turns freely around the axle. kind of confusing to understand. if this is the case, why are the axle and base keyed together?
    it seems to me that:
    the torque required to move the big spur gear should be much greater than the torque required to just move the mount around it. (a sort of clutch allowing manual movement)

    currently, under load, it just seems to spin the big gear without moving the mount part.

    fwiw, this is a good view of my mount:
    nexstarsite.com/Book/Updates/GTAzimuth.htm

    i'm guessing from the discusson on that page that it's possible my red fiber disk got greased.

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    Default

    Strip clean and reassemble - making sure lube is only where it is supposed to be!
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  7. #7
    abrocket's Avatar
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    Default

    yay. all ok now.

    I am posting this for anyone else in the future that might notice a similar problem.

    what i did: cleaned the fiber disk. actually.. i gave it good sanding to rough it up, and cleaned all the grease off the big gear.

    in retrospect ... i think this was the root cause of the problem. most likely the fiber gear was intermittently slipping causing the azimuth to behave erratically.
    this was probably because after years of work it had gotten worn down and a little slippery in places. it just needed to be roughed up a bit to make it behave. .... just like my brother when we were kids. :P

    the motor that i thought was the problem works just fine, but I had not ever tested it independently outside of the mount with no load.

    during one of the reassemblies, I had greased the big gear where I shouldnt have.

    lessons learned (as my project manager likes to say):

    lots. I know how to tear down and re-assemble the whole mount
    dont get grease where it's not supposed to be.
    check all components independently first
    study all information available before attempting to disassemble / reassemble. ( i know I got it wrong a couple of times while learning how to do it right)

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    skinnyonce (08-27-2011)

  9. #8
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    Default

    Thanks for the heads up !!!!
    Found a guide for doing the same thing to a CG-5 mount , some day I'll tear her down and regrease and debur the moving components of the mount,,

 

 

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