How much misalignment for Shaft-couplings

[geoff_p]

How much misalignment can so-called "Flexible Plum Coupling Shaft Coupler" take?

I'm building-up a mill from a bought-in X-Y Table, and the stepper-motors are hugely bigger than my old efforts had - about 800 oz-inch.  I also bought some Flexible Plum Couplings and I'm making "adaptors" to bolt the motors in-line with the leadscrews.

I have tried them in a lash-up but for the real jobby, I'd like to keep the alignment within acceptable limits, hence my question.

Geoff.

A prosperous New Year to all of you.

[BaronJ]

Hi Geoff,

The short answer is as little as possible.
These types of coupler are intended to allow for a small amount of angular and very little or no radial misalignment.  If you have just angular misalignment, then bellows type couplings might be better.  Bellows type won't allow any backlash either.  Don't forget the insert is flexible and will introduce backlash, particularly if the loading is high.

If I were using direct drive from a stepper or servo motor, I would use a rigid coupling and make the mounting holes slightly oversize so the you can align the shafts accurately.  If necessary using pined plates to fix the screw hole locations.

HTH.
 

[steampunkpete]

Look at the manufacturers catalogue.  That will give you limits on the angular and // off-set mis-alignments.

If you have no manufacturer or part number, then measure up and find the nearest equivalent in a manufacturer's catalogue.

[Deko]

An Oldham coupling should cope with both types of misalignment.

Cheers Dek.

[steampunkpete]

Baron is quite right of course, it's best not to have to deal with any significant misalignment because of the additional frictional forces which will absorb power and may reduce the accuracy of the control system.

[snub]

I found some info in my "notes", when I was looking at using some Oldham couplings for a project. I'm guessing these are maximums.

Parallel Offset-.004"
Angular Offset- .5 degrees

This link is to a company that specialises in stuff like this. They may have some technical info:
http://www.sdp-si.com/web/html/products.htm