I am using a Nema 24 on my Warco WM 290V [ 4 Nm allegedly] running 1:1 & it is underpowered on heavy roughing cuts, I'm thinking of going to a 2:1 ratio which should improve things I think.

Tony

If you buy closed loop stepper motors you can have an error signal to stop things if there is an issue with lost steps. It may cost more initially but you are only doing this once so may be a consideration. If you then have a slightly smaller stepper motor the occasional times you try to move things either too fast or too hard the error signal will trigger. Leadshine make closed loop driver and steppers but there are probably others, I haven't looked for a while.

This photo is of a rotating ball nut operating a push/pull ballscrew connected to the carriage. Note the small stepper motor. It is a Leadshine 3 phase closed loop matched to their driver unit.

Martin C

The power supply for stepper motors is an important consideration. I have a NEMA 24 4Nm stepper directly driving the Z axis on my Champion V20 mill. I use a 40volt DC home made linear power supply and the system has more than enough power to lift the head without any other assistance.

That suggests to me that problems with lack of torque are possibly due to poorly set up drivers or too-weak power supplies.

Which is why I was interested in the drive being used – limited testing with a couple of cheap single chip solution drives (Toshiba TB6600 & TB67S109ATFG) and a Stepperonline digital drive on a 2.2Nm Nema 23 motor from Arc Eurotrade has shown noticable differences in performance using the same 36V power supply.

The digital drive from Stepperonline performs much better than the other two – quieter, much less resonance & the motor warms up more, suggesting that the current is higher than the cheapies (not had a meter in circuit yet to check the actual currents) . This drive was more expensive, but not outrageously so (£13 delivered versus £5-6 each for the cheapies) but is rated for 50 V DC supply or 36V AC compared to 30 or 40V for the others – I have yet to try a 48V supply with the Stepperonline drive, as it only arrived last week.

Testing so far has not involved driving anything, just the motor alone being driven while hand held (the resonance can be so bad with the cheapies it dances about on my desk) & it may be that adding a driven load will change things (just adding an aluminium pullley changed the resonance somewhat).

Nigel B.

I did quite a bit of work on the 'rattle dampers' – fitted one to each axis of my small CNC router, which upped the rapids hugely Also fitted one to the stepper on my rotary table/hobber, which likewise upped the max rates tremendously. For the life of me I cannot find it in all my posts on this forum! No search mechanism here helps…

Anyway, I don't wish to contaminate this thread with info on all that, but to extract the available torque from a stepper requires that the correct supply voltage be used – as high as possible – to overcome Di/Dt at high(er) rpm's, where torque will fall anyway, but if the supply volts are as high as possible, at least that will not cause premature loss of torque.

Another critical element is stepper acceleration. If accelerated very slowly you would normally not have any issues – and unless really undersized, no steps easily lost. This would be the typical use in an auto-feed say on a mill axis, where acceleration is not normally an issue. It is a different matter on a NC application, where rapid moves are at high(er) speed, so acceleration tuning becomes key.

However, a stepper can also lose steps, and even start to go in reverse(!) when it hits bad mechanical resonance.

Coupling the stepper to the machine shifts the resonance point, but it is still there. Coping with this resonance is achieved in two ways – acceleration through the resonance point(s) as quickly as possible, fitting a flywheel to force the rotor through the resonance without stalling, or fitting a viscous or rattle damper.

There is a lot of info available of the design of a viscous damper, and they work very well – are the best type. However, it is still almost impossible to design one in the hobby shop, as you need to know so many paramaters regarding the machine the stepper is driving – all inertial masses, friction coefficient, damping constants, stiction, etc – nigh on impossible for the hobby man to measure.

My rattle dampers were a fair suck on both thumbs – first I found the resonance point of the system ( stpper mounted on the machine) where the stepper would stall or lose steps. Then I added a plain flywheel and sized that till it no longer occurred. Then search for new resonance point and change the flywheel circumferential mass till that resonance no longer caused a stall – then checked the first resonance point, etc…

When resonance was no longer an issue of concern, I then pushed the stepper acceleration , till it stalled or lost steps, and then drilled out that flywheel and fitted mild steel slugs – rods – as close to the periphery as practical. I found the acceleration achieved was then easily 2 to 3 times more, before problems reappeared.

Unlike the viscous damper, there is NO design info, patent, or published science on the rattle damper..

But is does work very well indeed, even if you have to become a little infantile and suck your thumb.

I have no idea if my 'design' is optimal, or what can be done to make it better, but the concept does seem to be effective over a broad design envelope, and very forgiving of error margins. But do the flywheel versus resonance thing first – the flywheel alone already enabled around a 1.2 to 1.5 times acceleration increase.

High stepper acceleration is not required as all, for powered axis drives, lathe auto-feed drives, mill Z axis raising, etc. I doubt you will need more than a 2NM stepper to lift the bench top mill Z axis, with a good ratio drive between stepp and leadscrew. If you accelerate slowly all will be fine.

However, electronic threading on the lathe, or gear hobbing is different. When pushing the envelope – high RPM ( 150 to 400) and large thread pitches ( 3mm say) require that the stepper accelerate the leadscrew ( and carriage) very rapidly to ensure the cutting tool and thread being cut are in synch when starting to cut the thread. Lost steps here are a major pain.

And there's the dissertation again. I have a few very detailed posts on these subjects, on the forum – can't find them…penalty for posting to much rubbish.

Joe

Link to Joe's rattle damper

**LINK**

scroll down to 07/11/18

Just interchangeable terms, I think.

Martin.

Temperature of stepper motors is not a good guide to a good system. As hybrid steppers monitor position the matched drivers back off the current when they are stationary so in practice do not get hot doing nothing.

Like Blowlamp my experience with hybrid closed loop stepper systems is no resonance on lathe or mill.

Martin C

Sorry to be a latecomer to the party on this one but I have just completed the fitting of the Clough42 ELS to my Myford Super 7 Big Bore lathe. I have done a write up which might help others with similar machines. The main head scratching was how to couple the encoder and the servo to the Myford but this worked out well in the end.

**LINK**

Pic of motor and encoder on my 254.

For anyone interested I did some work on the Clough42 software.
Adding; custom threads, thread to shoulder, multistart threads and a few other bits and pieces.
You can pull them down from **LINK**