Coupling Help

[Gorillakilla]

I am looking into coupling my stepper motors with lead screws and have a few questions. I have been looking at the 3-piece Jaw type coupling from Lovejoy , but searching on the forum has brought to my attention the U-type coupling. I can not seem to find this on the Lovejoy website.

Second I was wonder about couplers in general. The output shaft of my steppers are smooth with a flat grounded on one side. Most of the couplers I've seen just have a smooth hole bored into them. What would stop the motor shaft from just spinnig inside the coupler? Shouldn't there be something like a pin or small bolt to keep the two locked together?

[sendkeys]

Most i have seen are hooked in by a setscrew(s) or by a screw that clamps around the shaft.

I would go with the clamp type so you get less backlash.

[DareBee]

A Lovejoy type coupling has too much backlash for stepper/servo use you need a zero play cuopling such as the 1 shown above. check out mcmaster.com or misumiusa.com

[Karl_T]

Originally Posted by DareBee A Lovejoy type coupling has too much backlash for stepper/servo use you need a zero play cuopling such as the 1 shown above. check out mcmaster.com or misumiusa.com

????

Has anyone double checked that this is a fact? My CNC mill is built so that this is the only coupling that can be used. It an Excello model 602. Built that way at the factory.

Its been a while, but I think the servos on my Mazak M4 22" x 72" CNC lathe are coupled this way also.

Personally, I'm skeptical that LoveJoy couplings have backlash at the <relatively> low forces involved. For servos that are face mounted, I don't see any other solution.

Karl

P.S. to the OPs question, I installed a woodruff key on the shaft and broached a keyway on small lovejoy couplings because the torque a set screw will hold is WAY under what a servo can provide. Over time, this arrangement will almost certainly wear loose and be a huge source of backlash.

Karl

[Al_The_Man]

LoveJoy is a brand name not a type of coupling, although it has come to mean this, Lovejoy make a few kinds, the U or Uniflex type as mentioned in the first post can be found on http://www.lovejoy-inc.com/uniflex.htm they can be obtained up to very large HP. I have used them on servo applications with zero backlash.
The problem with using the bellow or accordion style for motors is it is best to use stainless as aluminum does not have the torque capability and fracture prematurely.
The aluminum ones should be used on encoder drive.
Al.

[JFettig]

There is a tiny amount of backlash in lovejoy couplers, If you have a zero backlash setup I would recommend another coupler but when you already have a little backlash and conpensate for it, you wont notice what you get out of a lovejoy coupler.

Another thing, if you do mount it up with a lovejoy coupler but they arent 100% aligned, this will actually remove the backlash you had.

Jon

[DareBee]

You are correct LoveJoy is a brand name and when I hear LoveJoy I automatically think "Spider Coupling", as it would seem most of you do as well.
Regardless of what some machines may or may not use; a Spider coupling is NOT a zero backlash coupling.
A face mounted servo should/can have a hole in the mounting bracket for wrench access to the capscrew that holds the "Helical Beam Coupling" in place.