By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Until July 27th

Stepper power for autofeed on lathe

All Topics | Latest Posts

Search for:  in Thread Title in  
Phil Grant09/10/2018 20:46:50
21 forum posts

Hi,

Been having a read through the forum as research for adding a stepper motor to my Warco super mini lathe autofeed.

It looks like the kit Myfordby uses in his youtube video is favourite at the moment.

I've designed and made a bracket to replace the gears at the end of the lathe using a Nema 23 stepper motor and I was wondering if anyone has a suggestion as to the power needed for the stepper, is 3Nm OK or too much.

I've fettled the leadscrew mounts and it turns freely by hand with no load but not sure what sort of torque will be required when cutting.

I'm using a stepper motor with a simple speed control at first but looking to add an arduino into the mix later for thread cutting and maybe adding another stepper to the cross feed later to dabble in a CNC conversion maybe......

Thanks for any help.

not done it yet09/10/2018 21:19:25
3028 forum posts
11 photos

Feed rate for surface cutting is one thing, but advancing 2.5mm per spindle revolution may need rather more power, I would guess? Not thought whether 3Nm is enough or too much.

John Haine09/10/2018 22:22:17
2545 forum posts
132 photos

The Z feed for my Super7 CNC conversion uses a type AC5707645251 size 23 stepper motor that came from Arc Euro Trade (I think they no longer stock these). Googling it says that it's rated torque is 180Ncm - what a ragbag of units! But that's 1.8 Nm. There's a 2:1 toothed belt reduction between motor and leadscrew. I have never had a problem with inadequate torque either surfacing or screwcutting. The leadscrew pitch is 1/8" so slightly larger than yours. I can't see why more torque would be a problem? The driver is the ubiquitous 2m541 type, also from Arc, supply ~40V and probably running peak current of 2.5A or so.

Phil Grant09/10/2018 22:56:22
21 forum posts
Posted by John Haine on 09/10/2018 22:22:17:

The Z feed for my Super7 CNC conversion uses a type AC5707645251 size 23 stepper motor that came from Arc Euro Trade (I think they no longer stock these). Googling it says that it's rated torque is 180Ncm - what a ragbag of units! But that's 1.8 Nm. There's a 2:1 toothed belt reduction between motor and leadscrew. I have never had a problem with inadequate torque either surfacing or screwcutting. The leadscrew pitch is 1/8" so slightly larger than yours. I can't see why more torque would be a problem? The driver is the ubiquitous 2m541 type, also from Arc, supply ~40V and probably running peak current of 2.5A or so.

Thanks for the info.

Phil Grant21/10/2018 11:20:22
21 forum posts

Hi,

Went for one of these in the end **LINK** with a DM542T controller and 24V power supply direct from stepperonline delivered from the UK.

Quite reasonably priced and delivered in a few days.

Got it all on the bench working with an Arduino using Accelstepper library.

Got to get some sort of user interface together then attach it to the lathe.

Muzzer21/10/2018 11:36:30
avatar
2904 forum posts
448 photos

Most of the hobby people just go on the basis of what others have found to work. The reason being that it's not easy to measure or estimate the required torque and speed extremes. And even then, to describe a stepper as "1.8Nm" is often unhelpful. I doubt if many of them could actually muster that level of torque to begin with - and it falls off very rapidly with speed.

You'll notice that the Chinese outfit you used also sell clones of the Leadshine "integrated easy servo" stepper motors. These combine the stepper driver module into the motor, along with an encoder on the motor shaft. This requires a lot less messing about to connect up the driver (just provide the step/dir signals and DC power) and being closed loop, it won't suffer from lost steps and can recover from a temporary overload. That's many of the advantages of a true servo with the cost of a stepper - and no external amp / driver, cleaner wiring etc. That additional level of control robustness means you don't need such a large margin of safety on the torque to guard against loss of position.

Incidentally, as the torque from a stepper motor drops off roughly proportional to speed, there is usually no advantage in creating a step-down reduction by using gears or pulleys. The effect of such a reduction is to make the motor run at twice the speed - and about half the torque. The net result is simply a reduction in the maximum speed of the output shaft, which is a problem for stepper motors to begin with. You are generally better off driving the leadscrews directly with steppers.

Murray

Martin Connelly21/10/2018 12:47:59
avatar
845 forum posts
95 photos

I use small Leadshine hybrids on my lathe. I do have a timing belt drive though because I spin the nut to push and pull the lead screw attached to the saddle. The driven pulley is threaded onto a bush that fits into a pair of flanged bearings and allows backlash elimination by squeezing down on the two bearings that sandwich a fixed plate between them. The reason for this system is that it allows modification with minimal change on the lathe so it can be reverted to manual if required. The downside is that you need to allow for a leadscrew sticking out of the tailstock end.

If you are not after rapid motions a large motor is overkill. Hobby use is not usually looking to shave seconds off a job.

Martin C

SillyOldDuffer21/10/2018 12:56:18
4415 forum posts
957 photos

Posted by Muzzer on 21/10/2018 11:36:30:

...

Incidentally, as the torque from a stepper motor drops off roughly proportional to speed, there is usually no advantage in creating a step-down reduction by using gears or pulleys. The effect of such a reduction is to make the motor run at twice the speed - and about half the torque. The net result is simply a reduction in the maximum speed of the output shaft, which is a problem for stepper motors to begin with. You are generally better off driving the leadscrews directly with steppers.

Murray

I love this forum! Thanks to Murray, I realised my understanding of steppers was adrift re their relationship to gearing and did some emergency googling.

I found this graph with description here which is illustrative as an example.

Very educational.

Ta

Dave

Martin Connelly21/10/2018 13:17:10
avatar
845 forum posts
95 photos

I don't think that graph applies to hybrid stepper systems. They are supposed to have superior dynamic torque compared to standard stepper motors.

Martin C

Edited By Martin Connelly on 21/10/2018 13:24:50

Martin Connelly21/10/2018 13:22:38
avatar
845 forum posts
95 photos

img_20181021_125704.jpg

This is how I have my lathe set up for the Z axis drive. The leadscrew is 16mm if you are wondering about sizes.

The leadscrew connects to a plain rod to push/pull the carriage. This type of setup also allows for testing the drive torque with minimal changes to the lathe if you are experimenting with different systems.

Martin C

Phil Grant23/10/2018 22:27:41
21 forum posts

Getting to grips with the Arduino controlling the stepper motor, waiting for some parts to mount it on the lathe but in the meantime I designed and 3D printed an end cover with cable management to fit with the flexible plastic tubing I have for protecting the cables.

If anyone is interested I can post the STL file on Thingiverse.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Ausee.com.au
Warco
Eccentric Engineering
ChesterUK
Meridienne Sept 2019
TRANSWAVE Converters
Eccentric July 5 2018
Allendale Electronics
emcomachinetools
Sarik
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest