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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Converting Torque rating, looking for a coupler
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  1. #1
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    Converting Torque rating, looking for a coupler

    I am trying to find a good coupler for a NEMA 23 stepper.
    I have had bad luck with the "spiral" aluminum couplers that were shipped with the motors from automation technologies.
    The motors are rated as 570 oz-in. holding power, I suspect that there are many variables the would change what the motors deliver to a coupler.
    Couplers are rated in "in-lbs" I tried using one rated at 8in-lbs and it did not last very long.
    I would like to use one that would stand up to a crash/stall out the stepper......
    I found these two:
    https://www.mcmaster.com/2764K226/
    https://www.mcmaster.com/2764K318/

    Rated at 18in-lbs and 44in-lbs

    I would need to add a spacer in the mount to use the 44in-lbs one.

    Looking for advice.

  2. #2
    Community Moderator Al_The_Man's Avatar
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    Re: Converting Torque rating, looking for a coupler

    If the couplers you used were helical aluminum they should be of the stainless steel variety.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
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    Re: Converting Torque rating, looking for a coupler

    Hi 570oz.in is 35.6lb.in so the 8in.lb is really underdone. They will also quote a failure load or Safety Factor which is usually x2. So you are going to need the 44's or more... Peter

  4. #4

    Re: Converting Torque rating, looking for a coupler

    As for the conversion, 16ozf = 1lbf, so 570ozf*[1lbf/16ozf]*in= 35.625lbf-in

  5. #5
    Community Moderator Jim Dawson's Avatar
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    Re: Converting Torque rating, looking for a coupler

    My Haas has this style, seem to work fine. https://www.mcmaster.com/bolts/clamp...-couplings-11/

    And I use these on my lathe, expensive but they work well. https://www.automationdirect.com/adc...eam%22&start=0
    Jim Dawson
    Sandy, Oregon, USA

  6. #6
    Community Moderator Al_The_Man's Avatar
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    Re: Converting Torque rating, looking for a coupler

    The SS ones in the Automation Direct are the ones I used, the aluminum variety I reserve for encoders only.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  7. #7
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    Re: Converting Torque rating, looking for a coupler

    I bought those coupler Jim listed above:
    https://www.mcmaster.com/bolts/clamp...-couplings-11/
    Mounted up great, seam a bit stiffer than the jaw type coupler spiders I am used to but that are a great fit.

    Thank you !!

    I now have a different issue, I think it’s actually the cause of the lighter coupler failing in the first place.

    I’m running a G0704 converted to CnC with and Automation Technologies kit. My x axis binds at the far left end (furthest away from the stepper).
    This has been that way from day one, there are a bunch of posts regarding poor quality ways on these mills.

    I haven’t ran into issues on it because I had it set up for acceptable travel and “play/slop” in the middle of the table but I am now trying to machine a part the uses almost all of my x travel.

    After installing the new coupler it machine the first 4 perimeter passes fine, then lost steps, retracted in Z, moved from right to left and promptly crashed into the part…..

    I am contemplating cutting off the dove tails and bolting in some Hiwin 15 clone linear rails…..

    The parts will be about $200, I am lucky to have access to a large manual mill at work to cut up my table and saddle….

  8. #8
    Community Moderator Jim Dawson's Avatar
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    Re: Converting Torque rating, looking for a coupler

    An ambitious project. But if you have the equipment, then I think it will work great.
    Jim Dawson
    Sandy, Oregon, USA

  9. #9
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    Re: Converting Torque rating, looking for a coupler

    Hi,
    I used the small diameter aluminum helical couplers on my original mini-mill. The steppers were fairly low torque approx 90oz.in but were direct connected to low lash
    planetary gearboxes of 10:1 ratio. The manufacturers spec for the combination was 705oz.in, quite respectable.

    I found after a short period of use that the helical couplers would 'wind up' in one direction and 'un-wind' in the other. I was trying to establish 1um resolution, and the ballscrews
    and gearbox should have been capable of 0.7um....so I was perplexed as to why my repeatable resolution was no better than 4um. That was when I noticed the lack of torsional rigidity
    of the couplers...and hence the loss of resolution.

    I thought.....'right, I'll have to replace those with something better'. What I discovered though was that if I crashed the machine, and I did have a couple of decent crashes in the early days,
    that the helical couplers would shear off, being the weakest link in the rotational/linear chain and thereby prevent damage. So I decided that I could live with 4um because I liked
    the fact that I had what amounts to a 'mechanical fuse'. I used the machine that way for seven years.

    My new build mill has 750W servos direct coupled to the ballscrew, therefore I could not tolerate the loss of repeatable accuracy with helical couplers. I use double-diaphragm couplers,
    the diaphragms being made of stainless and they are perfect, and only about $50 for the three of them.

    Craig

  10. #10
    Community Moderator Al_The_Man's Avatar
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    Re: Converting Torque rating, looking for a coupler

    Quote Originally Posted by joeavaerage View Post
    Hi,
    I used the small diameter aluminum helical couplers on my original mini-mill.
    I found after a short period of use that the helical couplers would 'wind up' in one direction and 'un-wind' in the other.

    Craig
    Hence the reason for using S.S. versions.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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