Stepper Motor Flexible Coupling.

[Brian AbbottParticipant @brianabbott67793]

Does anyone know where I can get on of these in the uk?

6.35 to 12mm

Thanks.

[Brian AbbottParticipant @brianabbott67793]

Where can i get one?

[SteviegtrParticipant @steviegtr]

Look up flexible couplings they are quite popular. Sure there will be a stockist near you.

Steve.

[JourneymanParticipant @journeyman]

Amazon, where else?

John

[Ian McVickersParticipant @ianmcvickers56553]

Hengstler or flexible beam couplings are pretty common so should be easy to find. RS components have then but they are a bit pricey. Zapp Automation might have them.

[Brian AbbottParticipant @brianabbott67793]

Thanks all.

John, looks like what I need, thanks for the link.

[Ketan SwaliParticipant @ketanswali79440]

If you are converting something to CNC, they flex/bend and can sometimes bend/snap the leadscrew. 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.

If you have alignment issues, better to look at oldam couplings, similar to this. These hold the position better. ARC will stop selling these after they are sold out becasue we stopped selling most things to do with CNC.

Ketan at ARC.

[Brian AbbottParticipant @brianabbott67793]

Hello Ketan.

I was hoping to use it to connect a stepper motor to my rotary table.

[Ketan SwaliParticipant @ketanswali79440]

Posted by Brian Abbott on 08/05/2020 20:34:56:

Hello Ketan.

I was hoping to use it to connect a stepper motor to my rotary table.

Then not a big deal. Most people use flexi coupling, but we stopped using them very early on. We still use the oldham type for the rotary table conversions we build, for quicker assembly, and still to get over alignment stress/strain issues.

Which ever way you decide is fine. Good Luck.

Ketan at ARC.

[JourneymanParticipant @journeyman]

That's exactly what I did, used the same coupling see Journeyman's Workshop

John

[Ketan SwaliParticipant @ketanswali79440]

Posted by Journeyman on 08/05/2020 20:49:32:

That's exactly what I did, used the same coupling see Journeyman's Workshop

John

Thats a good write-up John.

Ketan at ARC.

[JourneymanParticipant @journeyman]

Thanks, no original thinking by me. Based on Carl Wilson's article in MEW 249. Works well although I haven't used it much.

John

[Brian AbbottParticipant @brianabbott67793]

Thanks John.

Good read and will be very useful.

[old martParticipant @oldmart]

An Oldham coupling could suffer with backlash if it gets worn, but those springy one piece type will not. However, as Ketan says, the Oldham is easier to couple up as there are no grub screws to tighten up.

[Ketan SwaliParticipant @ketanswali79440]

Sorry Old Mart,

That is not the experience we have has with Oldham Couplings!

JS and I spent a long time developing the modifications to the KX CNC machines as well as the modulations from manual to stepper motor modifications of the rotary tables…. more than 12 years ago, well before most on here started to come up with the ideas.

Before we put the modified rotary tables with stepper motors onto the market, we ran Extensive tests, especially with Steve Blackmore – the demolition king, to break them. After additions of several D.C. Needle roller bearings and Thrust NRBs and Oldham couplings to the assembly, such rotary tables became a lot more robust. Because of the cost of the modified rotary tables, most of our customers for them were and still are industrial users who consider them to be cheap!

The SIEG factory made two versions of the KXs. We sent them the Oldham couplings for all the KX CNC machines we sold, after seeing the failure under certain ‘abuse’ conditions using the various flexi coupling versions they fit as standard. The KXs sold by others have flexi, including the clones. To the best of my knowledge, not a single one of the KXs we supplied over 10 years, including the one we use has had a ‘backlash’ / failure issue due to the U.K. made Oldham couplings fitted into the ARC supplied KXs, which are more expensive to buy than the flexi couplings… even from original Oldham couplings makers themselves, and even they recommend these over their own versions of flexi, for industrial applications.

Until around 2017, Oldham couplings were not made or available in China. Even when they started making such couplings in China, they had many failures initially, and only recently, they have made improvements. Even so, the Chinese equivalent is more expensive than their flexi, and sometimes their similar ‘looking’ types are still not Oldham types, but are marketed as such. It would be wrong to compare an Oldham coupling with flexi, in our opinion. But, as I said earlier, it is up to the user and their application.

Ketan at ARC

 

 

Edited By Ketan Swali on 09/05/2020 22:31:45

[Colin HeseltineParticipant @colinheseltine48622]

Brian,

i bought the Oldham couplings I used on my rotary table conversion from HPC gears. They are still open.

Colin

[Ketan SwaliParticipant @ketanswali79440]

Also, forgot to say that Oldham couplings also have grub screws to fix/clamp them onto the shafts, and yes they are easier to couple up and are always better than flexi to maintain alignment without stress.

Ketan at ARC

Edited By Ketan Swali on 09/05/2020 22:35:37

[Michael GilliganParticipant @michaelgilligan61133]

It’s worth looking through the enormous range offered by RS : **LINK**

https://uk.rs-online.com/web/c/pneumatics-hydraulics-power-transmission/power-transmission-couplings/couplings/

Use the filters in the sidebar to home-in on items of interest.

… Most of their listings have a datasheet available.

MichaelG.

[Ketan SwaliParticipant @ketanswali79440]

The ones which ARC sells are made by HUCO.

Ketan at ARC

[Ex contributorParticipant @mgnbuk]

I would not use the spiral cut solid type as a motor coupling. They were designed to drive low torque loads such as resolvers and tacho generators and were not particularly reliable when used as intended.

A better solution is a jaw coupling with a backlash-free elastomer insert, like this

The clamp hub desgn is better than grub screws directly contacting the shaft (particularly if the shaft does not have a flat). This is the type of coupling that Denford originally employed on my Triac.

Be aware that there are "general purpose" types of this coupling that do not have a backlash-free insert – all the backlash-free ones I have come across have a red insert & require a firm push to engage the two jaws over the insert. As with an Oldham coupling the motor can be removed leaving the ballscrew jaw in place – unlike an Oldham coupling the insert is not subject to wear.

Nigel B.

[Michael GilliganParticipant @michaelgilligan61133]

All good stuff, Nigel ^^^

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

MichaelG.

[john carruthersParticipant @johncarruthers46255]

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.

[Ketan SwaliParticipant @ketanswali79440]

Posted by mgnbuk on 10/05/2020 10:19:43:

I would not use the spiral cut solid type as a motor coupling. They were designed to drive low torque loads such as resolvers and tacho generators and were not particularly reliable when used as intended.

A better solution is a jaw coupling with a backlash-free elastomer insert, like this

The clamp hub desgn is better than grub screws directly contacting the shaft (particularly if the shaft does not have a flat). This is the type of coupling that Denford originally employed on my Triac.

Be aware that there are "general purpose" types of this coupling that do not have a backlash-free insert – all the backlash-free ones I have come across have a red insert & require a firm push to engage the two jaws over the insert. As with an Oldham coupling the motor can be removed leaving the ballscrew jaw in place – unlike an Oldham coupling the insert is not subject to wear.

Nigel B.

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.

[Ex contributorParticipant @mgnbuk]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by mgnbuk on 10/05/2020 10:57:10:

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.

Nigel B.

.

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.

.

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

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