[tooManyHobbies]

It's time I started looking for some couplers. Anyone have a good source?

Do I need to pay attention to coupler torque specs, or are these steppers (<400 in-oz) too small to worry about this?

tom

[Jeff Davis]

Yes worry.

I had some problems with backlash when I tried to use small cheap helicals on some 381 oz.

I have used some from US Digital, and CNC Fusion sells some decent ones. Make sure they are about 1" in diameter or so, the 1/2" ones are not gonna cut it unless they are steel.


Jeff Davis

[Crevice Reamer]

You will want the clamping type. I have not tried these, but it's a good company and they look decent, if you can deal with the 1/2/1/4 shaft sizes:

http://cncrouterparts.com/product_in...products_id=51

CR.

[TXFred]

I have not tried them myself, but I've been eyeing the ones from Stock Drive Products. They seem to have the largest selection of sizes.

Fred

[Crevice Reamer]

I have not tried them myself, but I've been eyeing the ones from Stock Drive Products. They seem to have the largest selection of sizes.

Fred

Do you have a link?

CR.

[TXFred]

I can't link directly to them, so try this. Go here:
https://sdp-si.com/eStore/

On the left side, click on Couplings, then Helical, then Commercial Series. You will get a list, and you can refine by dimensions, material and torque rating.

Fred

[TXFred]

Do I need to pay attention to coupler torque specs, or are these steppers (<400 in-oz) too small to worry about this?

I noticed that nobody's addressed this question yet, so here's my non-expert opinion, formed by reading books and eating the brains of really smart people.

In my case, my motors are 381 in-oz. That translates to 23.8 in-lb.

In the case of torque on a coupling, the motor torque is only one of two factors. The other is the resistance of the table. The only time I should see the full torque is if my table stalls, either during a cut or by running to its movement limit. The rest of the time, I am expecting the torque to be less than the maximum.

Viewed another way, if it takes 100% of the motor's torque to move the table, then the slightest increase in resistance will cause the motor to miss a step, ruining your workpiece. You should be set up so that you're never demanding the maximum from the motor (and by extension, the coupler).

Many people seem to be using aluminum couplers. But from what I see on the SDP site, these couplers are rated at half the torque of my motors. So it looks like you can get away with a weaker coupler. What happens when you make a heavy cut, crash the mill, or run to the table limit is another matter. At that point the coupler will be overloaded.

Will it shatter? Doubtful. Will it bend? Maybe. Most likely, though, the torque rating is based on the amount of torque a coupler can transmit before it begins to twist and introduce backlash into the system.

This means that if you feed too fast, tighten your gibs too much, or cut too deep, you might get more backlash. So then you feed slower, loosen the gibs a touch, and make shallower cuts. It won't be the end of the world.

I'm still waffling on the issue myself. I can save $20-40 by getting the aluminum couplers and possibly compromise my build. Or I can get the more expensive stainless couplers and know that they'll take whatever my motors can give without complaint.

Anyway, that's my two cents on the matter.

[ger21]

Try these, rated at 28in-lbs of torque.
http://www.mcmaster.com/#9861t5/=4z5r2z

[ger21]

I believe these are the couplers that SDP sells. I have these and the specs match up.


http://heli-cal.com/db/Products/Search.php?SearchID=3&DatabaseID=3&ProductSeries[]=ACR&Search.x=49&Search.y=7

[Mike Nash]

The first note on the Helical catalog page for the 17 lb-in couplers I got at a great deal pretty much told me I couldn't use them.

Dynamic torque ratings are momentary values. For non-reversing applications, divide by 2. Divide by 4 for reversing applications

There is also another rating on these. For mine:

Torsional Rate - 0.28 degree/lbin

[Jeff Davis]

Aluminum couplers are fine, you just cant use the cheap little half inch diameter ones. Mine on my 381 oz motors are aluminum now but they are beefier then the original ones I tried to use that did give me some backlash problems.


Jeff

[ger21]

The first note on the Helical catalog page for the 17 lb-in couplers I got at a great deal pretty much told me I couldn't use them.

Mike, do you have the same ACR087-8-8 that I got for $5 each?

I'm using them with 250 oz-in motors and they're working great for a few months now.

[Mike Nash]

Mike, do you have the same ACR087-8-8 that I got for $5 each?

I suspect so. JPMA?

I'm using them with 250 oz-in motors and they're working great for a few months now.

Hmm, good to know. My intended usage was on a minimill and I've got the gibs cranked down a bit tight due to the "precision" fit, so I was a bit concerned about the reduced torque ratings. I'm figuring about 5 thousandths windup at 272 oz-in.

[ger21]

MPJA I think. I use them on a router, so that doesn't concern me too much.

[Mike Nash]

And that's the problem with initial names - too easy to scramble. And I knew it was MPJA too. :tired: But then I also know I've done that before. Marlin P Jones & Assoc and I "remember" it as JP Marlin & Assoc ??

[tooManyHobbies]

I ordered and received these couplers from McMaster-Carr: http://www.mcmaster.com/#6208k6/=55n5jo

Very nice and inexpensive ($24.93 ea). Rated at 42 in-lbs, peak torque.

The label on the package for them is for Rocom Precision Rotary Components. http://www.rocomcorp.com/

Can't wait to get going on the installation!

tom