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  1. #1
    Member Project_Hopeless's Avatar
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    Question Motor Coupling Question

    My ball screw kit came with 6.5x10mm motor coupling and I need 8x10mm. So I could drill out the ones I have. But I question how good these are to begin with.

    They are an aluminum alloy slit type with small 2.5mm screws to apply the clamping force. Wouldn't a slit type with set screws be better than the clamping type, less likely to slip?

    My steppers have a notch in the shaft for a set screw but the ball screws do not. If so do I grind a small notch in the ball screw shaft?

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  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Motor Coupling Question

    The clamping type have more holding power than the set screw type. My preference is the single screw clamp type.

    Jim Dawson
    Sandy, Oregon, USA


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    Community Moderator Al_The_Man's Avatar
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    Default Re: Motor Coupling Question

    Are these the helical versions?
    Generally it is wise to use stainless versions for servo's, the aluminum are typically reserved for encoders.
    Al.

    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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    Member coherent's Avatar
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    Default Re: Motor Coupling Question

    Be easier to reply if we could see a photo or link to what you have. I personally prefer Oldham style couplers. Cost a bit more but robust. Also fairly easy to machine/make if you have the means.



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    Member Project_Hopeless's Avatar
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    Default Re: Motor Coupling Question

    Quote Originally Posted by coherent View Post
    Be easier to reply if we could see a photo or link to what you have. I personally prefer Oldham style couplers. Cost a bit more but robust. Also fairly easy to machine/make if you have the means.
    This is it.

    Motor Coupling Question-img_1966-jpg

    I'm not sure but a single 3mm screw dosen't seem like it can be torqued down enough.



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    Default Re: Motor Coupling Question

    Quote Originally Posted by Project_Hopeless View Post
    This is it.

    Motor Coupling Question-img_1966-jpg

    I'm not sure but a single 3mm screw dosen't seem like it can be torqued down enough.

    This style works, but like coherent, I prefer Oldham style couplers. And yes, the style in the photo can be torqued down enough to do the job. Just be sure to use blue Locktite, because the screw can vibrate loose over time. You should use locktite, no matter the style.

    Gary


    The Old Man and the C -----NC


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    Member davida1234's Avatar
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    Default Re: Motor Coupling Question

    Be careful with Locktite. If you get it on the inside of the coupler and slip it onto the shaft, it can be very difficult to remove the coupler later on.

    BryggaCNC.com


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    Default

    Quote Originally Posted by Project_Hopeless View Post
    I'm not sure but a single 3mm screw doesn't seem like it can be torqued down enough.
    Coupler manufacturers wouldn't do this if it didn't work - especially in a 6mm or 8mm shaft size.



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    Default Re: Motor Coupling Question

    I didn't like those but they do work. Depending on how tight the machine is they can add backlash. I went for jaw type instead. Much happier with them.
    I didn't have the means to make some Oldham. Otherwise I'd have bought the insert discs and made some couplings for them.



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    Default Re: Motor Coupling Question

    My experience with these types of clAmping couplings is that they are basically crap without additional slippage prevention!! This is the result of work in industry on custom machinery and factory built machines of various types. What is worse the slippage is often hard to detect. By the way these are all professional builds where tolerances are tight, I’ve seen slippage on shafts as small as 6mm up to around 20-25mm. Believe me on the machines built in Japan the tightened the living hell out of the clamp screws and did loctite them.

    So personally I would not use such shaft clAmping solutions without a key way to prevent rotational slippage. By the way I’ve seen this slippage from steel and aluminum couplings and pulleys. Aluminum seems to be worse due to stretching so that is something to consider.
    Quote Originally Posted by Project_Hopeless View Post
    This is it.

    Motor Coupling Question-img_1966-jpg

    I'm not sure but a single 3mm screw dosen't seem like it can be torqued down enough.
    In my estimation they can’t be and I’ve worked with clamps using screws from 4-40 to 5mm. Often what happens is that techs try to stop slippage by tightening even more thus leading to broken screws.

    By the way often you will only realize that there is slippage upon disassembly. You will see the signs of rotational rubbing on the shaft that the coupling is attached to. One diagnostic tool is whiteout ink applied to the shaft & collar in a thin strip to register the two parts. If the strips separate then you have rotational problems. The problem is you can’t always access the shaft and coupling to mark.

    So I’m apparently in the minority here but my experience with these solutions, in an industrial setting, has been very mixed. Such couplings have their uses, especially if phase relationships need to be adjusted. In general though I find belt drives to be easier to deal with and with the right pulley mounting more reliable.



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    Default Re: Motor Coupling Question

    Quote Originally Posted by Arjay View Post
    Coupler manufacturers wouldn't do this if it didn't work - especially in a 6mm or 8mm shaft size.
    I wouldn't go so far as to say that. In my experience it is to their advantage to put a coupler in the kit whether it will work or not. You have to match the coupler to the job being done and with no other information other than shaft size, it is impossible to know if this is an adequate coupler.



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    Default Re: Motor Coupling Question

    Those miniature couplers won't make a huge difference. I'd just use direct drive couplings with two screws for that 8mm shaft man.
    Different when you drive a 500kg table set-up at high speed though, in these circumstances those couplings are necessary and need careful selection.



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    Default Re: Motor Coupling Question

    I prefer the clamping spider type couplers myself. Often they can be had with both a setscrew and a clamp. Take note, the one you have has a bit of torsional spring to it and this will increase your backlash.

    Good couplers are not cheap. https://www.anaheimautomation.com/pr...D=1206&cID=559



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    Member Mecanix's Avatar
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    Default Re: Motor Coupling Question

    Quote Originally Posted by maxspongebob View Post
    torsional spring to it and this will increase your backlash.
    Failed to see this until today, never used those torsional-twisties spring types anyway, seen them before though. You are actually correct... that L difference between pull/push must be huge. Why are those still being sold today?! A 'spring' for coupling (lol)



  15. #15
    Community Moderator Jim Dawson's Avatar
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    Default Re: Motor Coupling Question

    These are my prefered couplings https://www.automationdirect.com/adc...ervo_couplings

    Expensive but they work well, they use a bushing that is clamped to the shaft with the set screws.



    Jim Dawson
    Sandy, Oregon, USA


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