ELS and power needs

[notyetParticipant @notyet]

Just joined up because I found the tread about electronic leadscrews cos I need some info. I am fitting an electric screw drive but I am stuck at the motor part. I have all the electronic gubbins but I have no idea for the size of motor I need to actually operate it. I am fitting this to a Harrison M300     If anyone could give me some sort of guide or calculator to work this out it wuld help my project.

[John HaineParticipant @johnhaine32865]

You need to measure how much torque is needed to turn the leadscrew.  Wrap some string round the l/s handwheel and pull with a spring balance while the half nuts are engaged.  You’ll need to apply a multiplier of 3 or 4 for acceleration and cutting forces.  Divide by any reduction gearing you are apply.  Then select a suitable modern 2 phase stepper motor from Stepper Online.  I’d guess that one of the higher torque NEMA23 types would be suitable.  What driver do you have?

[HuubParticipant @huub]

I have lookup this lathe and is seems to have a 40 mm spindle bore. That is slightly larger than mine (38 mm). The sizes are “comparable”, mine weighs 290 kg.
I use 1.26Nm 56mm Nema23 stepper motors on all axis and that works OK for me. I guess, if you use 2Nm steppers and digital DM556 drivers (or comparable) you are on the safe side. But if you want/need high accelerations because it is a production machine, you need more power. Keep in mind that the rigidity of the lathe has to deal with these forces. The rigidity of my (BF290) lathe is the limiting factor, not the stepper motors.

There is something to consider. I still use the original lead screws. They have play but that doesn’t influence the result because I basically operate it  as a manual lathe. It is just that stepper motors are turning the handles, not my hands. My de/accelerations are modest to be sure it is the spindle that is positioning the tool without any overshoot due to high deceleration. Overshoot and play (backlash) would make the positioning a lottery ticket!

 

[simondavies3Participant @simondavies3]

FWIW I used one of these Closed Loop Steppers for my installation of Clough42’s ELS system.

 

I installed onto a Chinese 125mm centre height lathe and have never had any stalling issues, even when roughing down lumps of steel with 5-6mm doc.

Looks like that particular one is no longer available, but the picture shows the main details of NEMA 23 with 3Nm and a matching driver unit, purchased back in September 2020 so probably yet cheaper now.

Mine was installed in the void under the headstock and drives via a toothed belt and a down ratio of (I think) 1:2.
Best of luck,

Simon

[notyetParticipant @notyet]

Thanks very much for all the ideas and suggestions. I intend to mount the Stepper at the tailstock end of the machine and the bigger the better I think. Cash of course is a consideration, I don’t have money to burn, but then I don’t think any of us has really, so I am going to try to get this right the first time. My worry is, are these real Nm’s or Chinese Nm’s? It is always in the back of my mind when I buy things from China.

[John HaineParticipant @johnhaine32865]

Buy from Stepper Online, not the absolute cheapest but a good supplier for both motors and drivers.  I once bought a NEMA08 motor from an anonymous vendor on eBay for what seemed like a very good price.  It would have been great if not for the bits of ferrous swarf left in the motor.  Buy cheap buy twice!

[notyetParticipant @notyet]

Absolutely right John Haine, I will start a bit of a dialogue with them first I think. Is it worth buying a stepper with a built in rotary encoder or stick with the original plan of a seperate encoder?

I have not said but it is the Clough 42 kit I am going to use and already have most of the bits, I have yet to buy the stepper, the driver and a power supply. I have the rest I think.

[John HaineParticipant @johnhaine32865]

If I understand the kit correctly you need an encoder on the lathe spindle, not the stepper, so has to be separate.  Depending on the steps/rev you need you could make your own. I’m using Mach3 which only supports a single pulse per rev encoder, just uses a slotted disc on the back of the spindle and a slotted opto.  I guess the Clough kit must have both a 1ppr encoder for “indexing” (i.e. knowing where the thread starts) and another to track spindle rotation.

On my Super 7 CNC conversion the X axis is driven by a NEMA23 stepper through a 2:1 reduction.  The drivers (recently upgraded) are DM542T.  That could also drive a NEMA34 stepper, it can support up to 4.5A, 50V.  You only need an encoder on the stepper if it is a closed loop type in which case it needs a specific driver.  Frankly I think closed loop steppers or servos on a hobby lathe are a waste of time unless you are also fitting ballscrews and doing a full CNC conversion.

[John Haine]

On John Haine Said:

…..

On my Super 7 CNC conversion the X axis is driven by a NEMA23 stepper through a 2:1 reduction.  …..

Oops.  That’s the Z axis (longitudinal).  X axis is direct drive by a similar stepper.  I have fitted a ballscrew to the X (cross-slide), too hard to fit on the Z without major work to the carriage.

[John Haine]

On John Haine Said:

If I understand the kit correctly you need an encoder on the lathe spindle, not the stepper, so has to be separate.  Depending on the steps/rev you need you could make your own. I’m using Mach3 which only supports a single pulse per rev encoder, just uses a slotted disc on the back of the spindle and a slotted opto.  I guess the Clough kit must have both a 1ppr encoder for “indexing” (i.e. knowing where the thread starts) and another to track spindle rotation.

 

John, you are correct in that you need a separate encoder on the spindle. The Clough42 solution needs to have a high resolution encoder to operate successfully – I believe that I used a quadrature output, 200 PPr, thus 400 detection edges per revolution. The chosen encoder resolution is set in the ELS configuration file along with any stepper to leadscrew and other ratios (due to belt drive ratios, etc).

As far as I recall, there is no ‘index’ function, the ELS monitors the status of the spindle constantly.

Also, for the OP, the point of having an encoder on the spindle is to detect the spindle state. Putting an encoder on the stepper will not achieve that aim. You may have been confused by steppers with inbuilt encoders for use as closed loop steppers. Unlike John, I like the use of closed loop steppers (with their dedicated control box) since this more or less eliminates the risk of step loss – or at least alerts when this has happened. Unlikely to be an issue when screwcutting – unless you do so at elevated speeds – but important if you are significantly reducing a diameter with autofeed.

Simon

[RobinParticipant @robin]

I think the course most people sail is to fit way too much motor, run it as close to max Volts as possible, wind up the steps per rev and see how many opto isolators they can cram in between the PC and the stepper driver.

It seems to work, but apples are not the only fruit…

I am playing with a box of 3 PKP566, 5 phase stepper motors from Oriental Motor. 4A of 24VDC gives me 500 steps/rev and 0.4Nm of torque at 1800 rpm. I keep the torque/rev graph on the wall in case I start to doubt my recollection 🙂

Robin

[simondavies3]

On simondavies3 Said:

…..

As far as I recall, there is no ‘index’ function, the ELS monitors the status of the spindle constantly.

 

Hmm…not sure that’s a good idea!  I’m fairly sure that Mach4, LinuxCNC and UCCNC all use both an encoder with say 400ppr plus an index which generates 1 pulse per rev.  The high ppr is used so the controller can continuously monitor spindle speed and compensate if cutting forces slow it down.  The index tells it what the spindle angle is once per rev so it knows where to start the acceleration to take a cut.  In principle you could just use the ppr encoder but these pulses will be say 400 times faster so the controller is more likely to miss one.

[Tony Pratt 1Participant @tonypratt1]

I have a Clough42 ELS fitted to my Warco 290V which is way smaller and lighter overall compared to a Harrison M300, I’m using a Nema 23 running at a 1:1 ratio and using the 3 position gearbox to give a mechanical advantage the system works fine BUT is clearly on the edge of it’s power. I must confess I do not fully understand how to increase the stepper power input but obviously others do, it works for me so I will leave well alone and yes the encoder should read off the spindle.

My considered opinion is that the OP should use a Nema 24 for the reason outlined above and from distant memory the first stepper I purchased did not meet the stated torque so that is something to be aware of.

Tony

[mgnbukParticipant @mgnbuk]

A lot of talk of “NEMA” frame sizes, but little information about the actual rated torque of the motors used.

NEMA 17, 23, 34 etc is just a motor frame size designation – basically sets the mounting flange dimensions. A NEMA 23 frame motor can be had in several different torque ratings, so just saying “NEMA 23” isn’t that helpful.

Clough42 did a video here in which he did a lot of tests on the performance of various steppers & drives for his ELS project. Worth a look.

Nigel B.

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