Motor to lead screw coupling method

[nevilletParticipant @nevillet]

This is my small project is to control the X (and in the future) Y axis of a Sieg SX2P with stepper motors.

I’ve sourced a Nema 23-3Nm stepper motor, a driver and with some very basic Arduino code managed to get the motor turning at varying speeds and directions.

The next part of the project is to couple the 8mm shaft of the motor to the 12mm leadscrew.

I was thinking of making a tubular sleeve coupling in steel that had an 8mm hole in one end and a 12mm in the other and using grub screws to secure the shafts into the coupling.

This would of course mean that the motor is permanently coupled to the leadscrew but when the motor is deenergised the hand wheel should still be usable though stiffer than usual.

Any thoughts on this plan?

[bernard towersParticipant @bernardtowers37738]

you could always fit a dog clutch so you could disconnect completely as it could be stiff to turn with the motor connected and i believe that some of them lock up when de-energized.

[Michael GilliganParticipant @michaelgilligan61133]

Before you go making couplers … have a look at this:

https://docs.rs-online.com/5fa4/A700000011930125.pdf

Then browse the web for something with the same general design, but a more affordable price tag.

MichaelG.

[nevilletParticipant @nevillet]

Many thanks for the suggestions.

The coupling you suggest do offer some flexibility between the two shafts.
Amazon have a wide range including this one:

[Peter Cook 6Participant @petercook6]

When spun by hand stepper motors can generate fairly large voltages. Applying that voltage to the driver when it is unpowered may be a risk.

[Harry WilkesParticipant @harrywilkes58467]

Michael have used those when I was working very useful coupling.

H

[nevilletParticipant @nevillet]

On the voltages generated:

fast hand speed = 3.5V
Attached to a battery drill at max  = 57V

So when in manual mode best to disconnect the motor from the driver.
Would one wire off each winding be sufficiant?

[Graham TitmanParticipant @grahamtitman81812]

Easy enough to make piece of 1inch or 25mm dia bar two drills and a hacksaw about 15mins each

[Peter Cook 6]

On Peter Cook 6 Said:

When spun by hand stepper motors can generate fairly large voltages. Applying that voltage to the driver when it is unpowered may be a risk.

The motor generates a back emf when it is powered, and it usually rotates a lot faster when it’s powered as well, so this is not likely to be a problem. It never has been with my set up anyway

If you set the enable input on the driver board correctly the stepper motor does not lock up when stationary

[nevillet]

On nevillet Said:

On the voltages generated:

fast hand speed = 3.5V
Attached to a battery drill at max  = 57V

So when in manual mode best to disconnect the motor from the driver.
Would one wire off each winding be sufficiant?

Disconnecting motors and electronics is bad practice, don’t!  Motor windings being inductive store energy, and when disconnected the magnetic field collapses causing a voltage.  If there’s no discharge path, volts rise until the insulation fails somewhere.  You don’t want the failure to be in the motor windings or inside the electronics.  If it can go wrong, it will!  All to easy for humans to throw the disconnect switch at the wrong moment.

In normal operation a stepper controller is powered by up to 40V, maybe more.   It won’t be inconvenienced by a 3.5V back voltage, and the output stage will probably be robust well beyond 40V.   Like as not the Electronics Engineer who designed the controller has protected it.  And it’s decades since transistors were so delicate as to be called ‘three legged fuses’.

Is it likely the mill’s lead-screw will ever be spun fast enough to generate 57V?  If it ain’t bust don’t fix it…

Dave

[nevilletParticipant @nevillet]

Hi Graham,  thanks for your suggestion.

The hacksaw detail, was that to give the coupling some flexability?

[John HinkleyParticipant @johnhinkley26699]

Neville,

If you want to retain a form of direct manual control of the mill without the need for clutches or switching off the power, consider modifying your software to incorporate rotary controls to each axis, in the manner of the oft-quoted electronicleadscrew.eu site.  Watch the 2-axis video to get an idea of their operation in practice.

John

 

[John HaineParticipant @johnhaine32865]

Look for Oldham couplings.

[HuubParticipant @huub]

I converted both my lathes to CNC. The motor is coupled to the shaft using an Oldham coupler. I still can (and do) operate the lathe manual without disengaging the steppers. The handles are still mounted. In the last 10 years, this has never lead to a problem (tested drivers: TB6560, TB6600, TMC2209, DM556). Seems I don’t turn the handles fast enough to generate to much EMF voltage.
I am currently converting my Manual mill to CNC. To connect the steppers I will use “double diaphragm couplers”. Not for a reason, just to experience the difference.

If the steppers are engaged, the dials are small and you turn the handle, than you will notice the 200 steps/rev the stepper can made. This has a small but noticeable impact on the accuracy in manual mode.

[Stuart Smith 5Participant @stuartsmith5]

I used a toothed drive belt with a 40 toothed pulley on the stepper and an 80 toothed pulley on the left hand end of the leadscrew.

With the ‘enable’ pin disabled, I can still use the manual handle on the right without any noticeable notching. Doesn’t seem to cause any problems with the stepper driver or Arduino nano I used.

Stuart

[Graham TitmanParticipant @grahamtitman81812]

Yes the hacksaw or if you have one a slitting saw and i missed the drill and tap for the grub screw it works out a lot cheaper than buying  Oldham couplings.

[Martin CargillParticipant @martincargill50290]

I know it is not the answer for this problem but I once used a piece of braided air hose and two jubilee clips to drive a vacuum pump.

The coupling had failed as it had moved down the shaft and had eaten itself. As a temp measure I stripped out what was left of the coupling and fitted a piece of braided clear air hose to the two shafts using two jubilee clips. This was still working when we came to change to the correct coupling about two months later (the pump manufacturer was slow in providing a spare).

The motor was (from memory) rated at 3hp and it was spinning at 1425rpm.

 

Martin

[John Haine]

On John Haine Said:

Look for Oldham couplings.

If the stated prices are to be believed … ARC has some astonishing reductions !

https://www.arceurotrade.co.uk/Catalogue/Stepper-Motors/Oldham-Couplings/33mm-Oldham-Hubs—Clamp-Style—Aliminium

MichaelG.

[Russell EberhardtParticipant @russelleberhardt48058]

While thinking about the motor coupling, give some thought to the leadscrew support.  I found that a significant part of the backlash was a result of the leadscrew moving backwards and forwards as it was turned.  Eliminating that with adjustment gave too much friction so I modified it by adding two ball thrust bearings from ARC, one each side of the block, as shown in the pictures:

Russell

 

[nevilletParticipant @nevillet]

Looking at the Oldham couplings on AceEuro, there appears to be only one half and it’s missing the middle part.

Or am I missing something?

[bernard towersParticipant @bernardtowers37738]

All three parts are there for me except the centre piece for the 33mm coupling.

[nevilletParticipant @nevillet]

So if I order two of these do they automaticly add the centre part?

[Michael GilliganParticipant @michaelgilligan61133]

This ARC page seems to make more sense than the first one that I linked:

https://www.arceurotrade.co.uk/Catalogue/Stepper-Motors/Oldham-Couplings/19mm-dia-Oldham-Hubs—Clamp-Style—Aluminium

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

On John Haine Said:

Look for Oldham couplings.

If the stated prices are to be believed … ARC has some astonishing reductions !

https://www.arceurotrade.co.uk/Catalogue/Stepper-Motors/Oldham-Couplings/33mm-Oldham-Hubs—Clamp-Style—Aliminium

MichaelG.

Probably cheap as they don’t have any more of the middle bits to go with them! Out of stock and unlikely to be restocked.

My KX-3 has the same sort of couplings

[JasonBModerator @jasonb]

The hacksaw method only allows you to clamp the bit of 1″ stock to the shafts. It will not take up any out-of-alignment of the two shafts which the Oldham coupling does.

[Author]

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