Spider Coupling for lead screw



  • I was using the flexible couplings that bend a lot and are a bit springy. I wanted to replace them with the spider couplings (or are they called jaw couplings... with the red material in between). I noticed that since the red part is not permanently attached to the two "jaws," this resulted in the jaws separating and the lead screw falling off.

    The solution would be to fix the opposite end of the lead screw, but I just don't have room there right now. Has anyone tried any other solutions? I was thinking I could glue the red part to the two jaws, but that might defeat the purpose of that piece ... maybe someone has tried it before? Any suggestions?



  • @jml On another thread here it was said that (primarily) the cheap ones are separating easily but higher quality ones don't.
    I bought some from China (at least in a shop that made the appearance to have quality products - you never know until the order arrives) and I was unable to separate them by hand.

    So it appears you got a bad one.

    The solution would be to fix the opposite end of the lead screw

    I am not sure if I understand this how you mean it. I understand here to fix the screw at the motor and at the other end. This would be a bad idea because it will put a lot of strain to the lead screw if the fixing points are not 100% aligned (which is more or less impossible).
    In case you meant to swap motor position forget what I just said. 😉

    P.S.: also your guess was right, they are called jaw couplings. Depending on the exact type also zero backlash jaw couplings.

    P.P.S.: here is the thread I mentioned above.



  • @jml In my flexible couplings set at the bottom, I placed a 4mm ball bearing inside & removes the spacing inside to eliminate the compression of the coupling. It still can bend just fine.



  • @wilriker I did mean to fix the screw at the motor and the other end. If it was perfectly aligned then it would't be a problem, but nothings ever perfect, so it would probably be really hard to get it right enough to not cause binding like you said. Hmmm so I guess the best is to purchase new ones that don't separate.

    @Stephen6309 I'm not quite sure what you mean. Did you put one 4mm ball inside, or did you put the whole bearing assembly inside? And is the point to remove the spacing between the two shafts that are being coupled? I can see how removing that space would help, but I'm not sure how the ball would stay put (unless its welded or epoxied).



  • Hi @jml,

    I have high quality jaw couplings from Misumi and they'll separate if enough pressure is applied.

    My solution is to place 2 sleeve bearings very close to the coupling: one sleeve bearing on the steppers' shaft below the coupling, and the other on the lead-screw above the coupling, thus 'sandwiching' the coupling in between (but without actually putting any pressure on the coupling - just close enough to prevent it from separating).

    Here are a couple of pics to illustrate what I mean (in the second pic, everything has been stripped away except the coupling and 2 sleeve bearings to make it easier to see how they're placed in relation to one another):

    0_1540681290798_pic1.png

    0_1540681321303_pic2.png

    Hope this helps.
    SnowCrash



  • @snowcrash That seems like a good solution. But I was thinking that maybe that setup restricts the coupling from doing its job and it ends up being equivalent to a rigid coupling? Is it a spherical bearing?



  • I understand what you're saying, @jml, and you might be right. Can't say for sure. Seems to me that this setup gives just a bit of play which is better than rigid coupling, but perhaps not much. Plus I think the jaw coupling are better at reducing backlash, but again, perhaps it's just wishful thinking. Anyway, if anyone has a better solution I'd be happy to learn what it is 🙂

    It's worth noting that the bottom bearing (ie the one mounted on the stepper's shaft), is meant to protect the inner bearings inside the motor. I believe that together with the bottom part of the jaw coupling is does a better job at this than rigid couplings, but again, it's just something that seems logical to me, not something I can prove to be correct.

    As for the bearings, I'm using these bearings from Igus.



  • @snowcrash Oh those Igus bearings are spherical, so it will allow for some angular changes, so definitely different than a rigid coupling. I like that solution, and I like @Stephen6309 's solution, but I'm not quite sure how to implement it without the ball falling away.



  • @jml The bearing is inside the coupler, it won't fall when the stepper shaft and leadscrew are in the coupling.

    One way to install with a flexible coupling: with the motor shaft pointing up, install coupling, drop in bearing and then the leadscrew.



  • @stephen6309 ah makes sense now!


 

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