[devincox]

guys,
I have just finished making the parts for my x-axis stepper mount and before I snug everything up, I wanted to see if anyone had any good ideas on how to make sure the stepper was lined up with the ballscrew, as close as possible.

I thought I would use the coupler to help line up the stepper motor and then locate the holes for the final piece of the stepper mount. I thought it might be good to leave a bit of room in the mounting holes to allow for very minor adjustment.

Where is the best place to measure for misalignment?
Here is a link to a snap shot of my stepper mount.


Thanks,
Devin

[keebler303]

You could use a rigid shaft coupling to hold the motor in place and mark the holes. Generally you would use the round boss on the front of the motor for alignment. If you get it relatively close, you can use a "helical beam coupling" to make sure you don't have any binding from the misalignment.

Matt

[philbur]

Turn the the outside diameter of the coupling to be concentric with the bore then mount it on the machine an clock both ends of the bushing while rotating by hand. Adjust the motor location until both ends of the bushing have acceptable run-out.

You should have assembled the motor mount and bored the ballscrew bearing bores and the motor mounting bore at the same setting, then they would have been aligned by default.

Phil

[devincox]

I have already machined the rigid coupler as mentioned by Matt and was planning on using it to aid in alignment as also mentioned.

However, Phil's idea of machining the bores once assembled makes for an easier solution. I think the Y axis mount will get this treatment.

How much run out is acceptable in a situation like this?
What is it based on ? max speed , diameter, material ?

Not sure what I should be aiming for. I definately dont want to goof up the ball screw.

Thanks,
Devin

[philbur]

I think the main issue is the risk of radially overloading the ballscrew mounting bearings or the motor bearings. If you have a rigid coupling then out of alignment should be no more than a flicker on a 0.01mm indicator. This is why people normally use flexible couplings.

Phil

I have already machined the rigid coupler as mentioned by Matt and was planning on using it to aid in alignment as also mentioned.

However, Phil's idea of machining the bores once assembled makes for an easier solution. I think the Y axis mount will get this treatment.

How much run out is acceptable in a situation like this?
What is it based on ? max speed , diameter, material ?

Not sure what I should be aiming for. I definately dont want to goof up the ball screw.

Thanks,
Devin

[SCzEngrgGroup]

I have already machined the rigid coupler as mentioned by Matt and was planning on using it to aid in alignment as also mentioned.

However, Phil's idea of machining the bores once assembled makes for an easier solution. I think the Y axis mount will get this treatment.

How much run out is acceptable in a situation like this?
What is it based on ? max speed , diameter, material ?

Not sure what I should be aiming for. I definately dont want to goof up the ball screw.

Thanks,
Devin

You do NOT want to use truly rigid couplings! If you do, you are almost certain to end up at some point with either the motor shaft or the end of the leadscrew failing due to fatigue, unless you are incredibly lucky and get the alignment *perfect*. Even the tiniest misalignment will eventually cause a fatigue failure. Use a helical coupling, to allow that slight misalignment without stressing the shafts.

Regards,
Ray L.

[philbur]

The Tormach uses rigid couplings and I don't think anybody has reported a bearing failure. A number have reported coupling slippage however. On mine you can here the bearings working harder once a revolution though, particularly on the x-axis, so I would agree with Ray that it is best to avoid solid couplings if at all possible.

Phil

You do NOT want to use truly rigid couplings! If you do, you are almost certain to end up at some point with either the motor shaft or the end of the leadscrew failing due to fatigue, unless you are incredibly lucky and get the alignment *perfect*. Even the tiniest misalignment will eventually cause a fatigue failure. Use a helical coupling, to allow that slight misalignment without stressing the shafts.

Regards,
Ray L.

[devincox]

I found some helical couplings at anaheim automation for a decent price.

CPL-HC - Integral Clamp Coupling

Devin

[keebler303]

You can find similar prices and much better selection at mcmaster.com

Matt

[devincox]

You can find similar prices and much better selection at mcmaster.com

Matt

Mcmaster.com has a way better selection but I couldnt find anything better in price. After looking some more, I found the couplers for around 12.00 a piece at Anaheim, the lowest price I could find on mcmaster.com was $25.46.

CPL-HS - Set Screw Coupling

Thanks,
Devin

[skullworks]

Mcmaster.com has a way better selection but I couldnt find anything better in price. After looking some more, I found the couplers for around 12.00 a piece at Anaheim, the lowest price I could find on mcmaster.com was $25.46.

CPL-HS - Set Screw Coupling

Thanks,
Devin

And I hope you read the last line of the description...

"50 Piece minimum when ordering."

[SCzEngrgGroup]

It's pretty trivial to make your own Oldham couplings, and the cost is near $0. That's what I did many years ago when I converted an X2, and they work perfectly to this day.

Regards,
Ray L.

[devincox]

hmmm. I hadnt considered oldham type couplers. I think I will try that.

Thanks,
Devin