Warco WM18 – which Nema 34 for Z axis

[petro1headParticipant @petro1head]

Posted by SillyOldDuffer on 05/04/2023 16:01:44:

Posted by petro1head on 05/04/2023 07:01:05:

Not for CNC, just to powerfeed the Z axis running std screws

Most reccomend a Nema 34 but was wondering which one. Hopefully someone who has done this can advise

I am looking at THIS one?

…

I just put a torque wrench on my WM18 and lifting the head takes less than 20Nm. Unfortunately that's the minimum torque my wrench can measure so the answer isn't conclusive. A 12Nm Nema 34 is definitely in the right ball-park, but an 8Nm uncertainty is a shade more than I would care to risk £70 on.2

Dave

I agree and will probably get the 12Nm one

[JasonBModerator @jasonb]

Posted by SillyOldDuffer on 05/04/2023 16:01:44:

I'll have a think about how to measure the torque needed from first principles. I'll have to bodge something because I don't have a suitable spring gauge or a set of weights.

Lack of weights didn't stop you before Dave

[JasonBModerator @jasonb]

Out of interest I just tried the X3 and SX2.7, both of which have a 2:1 bevel gear. Used a 1/4 drive torque screwdriver as that goes down to quite low settings

X3 14lb in = 28 without the gear = 3.16Nm

SX2.7 12.5lb in = 25 without the gear = 2.8Nm

[petro1headParticipant @petro1head]

The problem with stepper motors is, as the speed rises the torgue reduces. So you buy a 3Nm one but as i gets the revs up, say 1000rpm, the torque is now only 0.5Nm

[JasonBModerator @jasonb]

But do you need anything like that speed?

If it's a metric machine they probably 2mm pitch screw, max travel maybe 300mm so say 20secs top to bottom and you only need 450rpm

If you feel you need it faster then just size the motor to give the torque you need at the revs you want

Edited By JasonB on 05/04/2023 18:26:13

[petro1headParticipant @petro1head]

Ok been doing some checks on my current setup.

The stalling happens when you first turn the motor on. The RPM is 253.

I can adust the Microsteps. Its currently set at 20/4000 steps/rev. If i change it to 25/5000 steps/rev it turns at 203 RPM and does not stall.

To be honest when i installed the stepper i did not fully understand what i was doing so guesed :0

So i am no wondering f i do need to upgrade to a Nema 34? Which will be quite expensive as not only will i need the stepper motor, a driver and a new power suppply (mine is only 6a and the Nema needs min 6a)

if anyone is interested i will start a new thread re Power Feed for Y axis on a Warco WM18

[SillyOldDufferModerator @sillyoldduffer]

Posted by petro1head on 07/04/2023 10:57:14:

Ok been doing some checks on my current setup.

The stalling happens when you first turn the motor on. The RPM is 253.

I can adust the Microsteps. … If i change it to 25/5000 steps/rev it turns at 203 RPM and does not stall.

…

So i am no wondering f i do need to upgrade to a Nema 34? Which will be quite expensive as not only will i need the stepper motor, a driver and a new power suppply (mine is only 6a and the Nema needs min 6a)

…

Not if it works! Stepper motors are interesting beasts, with a combination of "it depends" features.

• Power and Torque depend on Current – so make sure the power supply can deliver enough amps. Also, the electronic driver has a selectable current limiter to avoid overheating the motor. Set it to the maximum the motor will take. The motor can be overrated for short bursts, i.e. as long as it has time to cool down between lifts.
• Max Speed depends on voltage because high voltages help maintain pulse shape. For this reason it's better to use an unregulated power supply than a regulated one. Regulated supplies work OK, but they can't spin the motor flat out. Max speed also depends on the pulse rate available from the electronics, and the motor's ability to cope with fast pulses.
• Positional accuracy is determined by the microstep setting, which trades off against speed, torque, and power. For just lifting a milling head, positional accuracy doesn't matter. (Does if the head was being CNC'd)

So there's a relationship between steps, pulse-rate and the power supply that can be experimented with to produce a range of speed/torque relationships. If one of them provides enough torque to lift the head at a reasonable speed then all is good. I think lower numbers of microsteps per revolution are a better bet for torque than high micro-step settings.

That your motor and power supply lifts the head at 5000 micro-steps is promising. I'd certainly experiment more before spending big money!

Dave

[John HaineParticipant @johnhaine32865]

How are you generating the pulses? If the stepper stalls on switch on it may indicate that it needs and acceleration phase. On my xfeed I use grbl for control and the acceleration comes for free.

[petro1headParticipant @petro1head]

Posted by John Haine on 07/04/2023 12:31:36:

How are you generating the pulses? If the stepper stalls on switch on it may indicate that it needs and acceleration phase. On my xfeed I use grbl for control and the acceleration comes for free.

With one of these – https://www.ebay.co.uk/itm/325143354034

[petro1headParticipant @petro1head]

So, did some more testing and it still stalls, not as much but have decided to buy a Nema 34

[SillyOldDufferModerator @sillyoldduffer]

Posted by petro1head on 07/04/2023 21:32:52:

So, did some more testing and it still stalls, not as much but have decided to buy a Nema 34

The good thing now is you can be confident the bigger motor will work. As the small one had nearly enough torque to do the job, only moderately more oomph is needed. Apart having to spend precious money, ouch, over-sizing the motor means it won't get hot, and the extra power could wind the head up faster.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by petro1head on 07/04/2023 21:32:52:

So, did some more testing and it still stalls, not as much but have decided to buy a Nema 34

.

Obviously, I am guessing …. but I suspect that the problem is as much to to with the mechanics of the machine as the dynamics of the stepper motor.

I would bet that if you measured the torque very carefully you would find an initial peak, due to ‘stiction’ … and the poor ol’ stepper motor needs to overcome that before things get moving.

MichaelG.

.

Brief explanation of stiction here:

https://www.linearmotiontips.com/how-to-reduce-the-effects-of-stiction-stick-slip-in-linear-guides/

Edited By Michael Gilligan on 08/04/2023 10:01:44

[petro1headParticipant @petro1head]

Posted by Michael Gilligan on 08/04/2023 09:54:35:

Posted by petro1head on 07/04/2023 21:32:52:

So, did some more testing and it still stalls, not as much but have decided to buy a Nema 34

.

Obviously, I am guessing …. but I suspect that the problem is as much to to with the mechanics of the machine as the dynamics of the stepper motor.

I would bet that if you measured the torque very carefully you would find an initial peak, due to ‘stiction’ … and the poor ol’ stepper motor needs to overcome that before things get moving.

MichaelG.

.

Brief explanation of stiction here:

**LINK**

Edited By Michael Gilligan on 08/04/2023 10:01:44

I think you have explained it thanks.

I will report back once i have the new motor

I will also create a new thread re the Y axisvand i dont think i have seen someone do this on this sizevand type of mill.

Yet again cheers guys

[petro1headParticipant @petro1head]

Posted by Michael Gilligan on 08/04/2023 09:54:35:

Posted by petro1head on 07/04/2023 21:32:52:

So, did some more testing and it still stalls, not as much but have decided to buy a Nema 34

.

Obviously, I am guessing …. but I suspect that the problem is as much to to with the mechanics of the machine as the dynamics of the stepper motor.

I would bet that if you measured the torque very carefully you would find an initial peak, due to ‘stiction’ … and the poor ol’ stepper motor needs to overcome that before things get moving.

MichaelG.

.

Brief explanation of stiction here:

**LINK**

Edited By Michael Gilligan on 08/04/2023 10:01:44

I think you have explained it thanks.

I will report back once i have the new motor

I will also create a new thread re the Y axisvand i dont think i have seen someone do this on this sizevand type of mill.

Yet again cheers guys

[petro1headParticipant @petro1head]

Well I have now fitted the Nema 34, much better, no stalling

[JasonBModerator @jasonb]

Might help others if you say what torque rating you fitted as the "34" simply refers to the bolt hole pattern & overall size not how powerful it is.

[petro1headParticipant @petro1head]

Posted by JasonB on 14/04/2023 09:05:49:

Might help others if you say what torque rating you fitted as the "34" simply refers to the bolt hole pattern & overall size not how powerful it is.

It was the 8Nm one

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