Stepper Motor Flexible Coupling.

We have used Oldham couplings for many years in telescope drives using steppers and VFO drives, never had a problem from the antarctic to the equator.
Even using software and encoders to cancel backlash, scope drives are very sensitive to drift as any astrophotographer will tell you where mili arcsec pointing is the goal.

Yes Nigel, we had extensive arguements with SIEG over this type of flexi couplings too..., because, as MichaelG says, these too failed to dealwith axial alignment/mis-alignment, and still giving cut results under extream circumstances similar to what I said earlier: ' They put a strain on the lead/ball screw, and sometimes also effect the fast movement of the X/Y axis. So for example if you are cutting/engraving a circle, at a certain point you may fail to get a perfect curve. If you are looking at a clock face, usually between 6pm and 9pm.' Although I agreed with them that they were cheaper to obtain from within China and Taiwan, and the performance was/is much better than the OP type flexi coupling, and the curve was more near perfect.

This arguement became heated between SIEG and myself, we agreed to disagree, compromise and I couriered the Oldham couplings to them.

Regarding 'wear' for Oldham couplings, I agree with you and I wish there was, so that I could sell replacements to all the users of the products. But so far, in the 12 years we have been selling them, this has been rare.

Ketan at ARC.

provided that you can be sure of axial alignment between motor and shaft.

The elastomeric insert is tolerant of small radial, axial and angular misalignments - at least it will not metal fatigue and break like the spiral cut aluminium type do if alignment is less than perfect.

Ketan,

As I said initially, my industrial Denford Triac came fitted with Rotex brand jaw couplings to join the small (1.85Nm) brushless servos to the ballscrews. The machine has obviously had a hard life in industry, yet the couplings, ballscrews & support bearings are all OK.. Maybe Denford's machining was better than Seig's, so there was less misalignment to accomodate ?  I have no doubts about the quality of Huco products - at my last employment we used their couplings almost exclusively to couple encoders to motors - but in the 27 years i was involved in retrofitting CNC systems to machine tools I didn't come across any instances of Oldham couplings being used with servomotors.

Nigel B.

Edited By mgnbuk on 10/05/2020 11:06:45

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Sorry if I was not clear, Nigel ... I was comparing the properties of your illustrated coupling with the Oldham one, not the spiral cut aluminium type.

MichaelG.

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Edit: ___ Incidentally, the spiral cut is [in my opinion] a poor substitute for the aluminium version that has a staggered series of ‘half cuts’.

Edited By Michael Gilligan on 10/05/2020 11:09:32

Hi Nigel,

I am not trying to criticise what you are saying in any way. Apologies to you or anyone who has different coupler use/preference, if you feel that I am giving that impression.

I understand and respect your 27 years experience in retrofitting CNC systems, in which you did not come across any instances of Oldham couplings being used with servomotors. JS and I had the same discussions and arguments with the technical guys at SIEG,... some of whom came from experienced CNC backgrounds, just like you. With reference to coupling, SIEG could use what they wanted, and JS and I can use what ARC wanted, and others used what they wanted. SMITHY in the U.S. used the type of coupling you specified. We all have our own thinking and reasoning.

For rotary tables, Steve Blackmore was the demolition guy, and for the KXs, Adam Stevenson was the demolition guy. He was a bugger for sneaking changes in.. speed, feed, DOCs, especially during demonstrations at shows.. without thinking, and working on theories which seemed right in his mind, without considering the 'real world' limitations of small size machines. This issue of stress load on the shaft of small diameter ball screw which went into the coupling is something he figured out with John after overloading the KXs with increased speed/feed rates and DOCs, and this in not unique to SIEG. It is also difficult to prove/disprove that Denfords machining in this area was any better/different. Many Denford Triacs 'almost unsued' school clearances came onto the after market via auction sites as you know. When people who bought them off the auction sites went to Denford, they were referred to JS or ARC, because Denford did not want to deal with them. When such people called ARC, we referred them automatically to John. John liked to work on them, got good at it, and kept stock of the auction purchases of Triacs for conversion/updating and re-sell.

My apologies to the OP for possibly getting off-topic.

Ketan at ARC.

Edited By Ketan Swali on 10/05/2020 15:12:48

Apologies to you or anyone who has different coupler use/preference, if you feel that I am giving that impression.

No apology required on my part, Ketan. There are frequently many routes to the same end & our experiences tend to guide us - mine are just different to yours. Both of the coupling solutions we highlighted between us will do a better job for the OP than the spiral cut type initially requested IMO - but doubtless someone else's experience will say that type is best !

It would have been nice if my Triac had been a hardly used ex-school machine, but in that case it would doubtless have cost me more than the £100 I paid for the carcass of my industrial version - yet another alternative route !

Nigel B.

Thanks Nigel,

Just to show what I meant about the stress on the ball screws resulting in 'poor curve' between 6pm and 9pm, and that it was not unique to SIEG KXs, have a look at this You Tube video at about 6 minutes into the content. The cure for the KXs which ARC sold, as Adam and John discovered, was to use the Oldham couplings. I am not sure if Nerdly or Tormach ever figured out that the couplings they were using, was the probable real cause.

CAUTION: Although I have linked to Nerdly's YT video, I do not necessary agree or disagree with the contents. Most of the times, things are not always simple, one way or the other. I know Tormach, the factory they use (not SIEG) to make their machines, the methodology and people they have on their team, who I respect. There are at least two people on this forum who regularly use their Tormachs with great success, and their Pathpilot software is one of the best things which JS, AS, and Steve Blackmore have seen.

Ketan at ARC