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.

If the couplers you used were helical aluminum they should be of the stainless steel variety.

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

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

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

The SS ones in the Automation Direct are the ones I used, the aluminum variety I reserve for encoders only.

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….

An ambitious project. But if you have the equipment, then I think it will work great.

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

Quote:

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Originally Posted by joeavaerage

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

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Hence the reason for using S.S. versions.;)