If the couplers you used were helical aluminum they should be of the stainless steel variety.
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.
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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.
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
Last edited by StrawberryBoi; 09-19-2021 at 12:31 PM.
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
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.
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.
Jim Dawson
Sandy, Oregon, USA
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