1. #1

    I tried making a 4th axis using one of these cheap rotary tables off the bay


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    problem is, even if you exclude the stepper motor coupling, remove that altogether... one hand holding the input shaft, and the other on the chuck, you notice atleast 1mm of 'backlash' play.... unless you 'lock' it... which of course when used the way its intended (as a rotary table) is fine... but as a 4th axis its not.

    so.... need a new plan... I need an accurate way of controlling a 100mm chuck from a stepper motor with minimal backlash

    can anybody make any recommendations?

    ive noticed this
    CNC 4th Axis Rotary Table (100mm / 4 inch) with Flying Leads | eBay

    the description says

    Maximum backlash (all rotary tables are tested to be within this spec): 20 arc minutes
    Typical backlash (most rotary tables are shipped within this spec): 15 arc minutes
    but im not as clever as most on here... can anybody advise if 20 arc minutes equates to around 2mm of backlash? on a 50mm diameter? so...???

    any advice etc would be very much appreciated, so thanks in advance

  2. 1 degree on a 100mm dia chuck is 100*3.142/360=0.87mm

    20arcmnutes us .334 degrees so about 0.3mm
    Last edited by irving2008; 05-09-2013 at 09:51 AM.

  3. #3
    It sounds like you've not got the worm gear engaged properly. There worm gear is on an eccentric, so you can rotate the motor mount etc to push the gear into a tighter mesh, which will substantially reduce the backlash. There's a screw you undo, then the motor will rotate freely... it probably says in the instructions.

    The rotary table you linked to wont be any better than the one you've got if it's adjusted properly.

    P.S. You might want to put a grommet round the motor cables so that the aluminium plate doesn't cut them.
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  4. #4
    mekanik's Avatar
    Lives in Barrow in Furness, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 6-7 years. Has a total post count of 486. Received thanks 53 times, giving thanks to others 47 times.
    Hi M8
    Check to see if your eccentric is at it's maximum travel, if it still has some throw left you could strip the unit down and try lapping the pinion and wheel with solvol autosol or similar, and then if needed make a new eccentric with slightly more throw (if you have to remove a lot of material for a snug fit between pinion and wheel)

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