Mini Mill Conversion - best stepper drive choice

Mini Mill Conversion - most appropriate stepper drive choice

A friend and myself are separately working on CNC conversions of mini mills. Mine is an old Sieg X2, where I intend to go cheap and use trapezoidal screws and Delrin nuts - kind of as an experiment to see what's possible. My friend's is a bit classier - one of the larger cast iron Proxxon mills, where he's using decent ballscrews and hence expects decent results!

We are both intending to use 3Nm steppers - which we presume from reading around the forum seem appropriate. What we would like some input on, is the best choice of stepper drives to use.

I know the AM882 is the drive of choice for a router, where you would be wanting to run the motors at 68v to achieve higher speed operation. My understanding however is that for a small mill, you're really not looking for such axis speed, and hence could quite happily run the motors at a lower voltage. This in turn allows lower cost stepper drives and power supply, as well as reducing heating effects in the motors.

Is this a reasonable argument? Or not? And if so, what are the "preferred" stepper drives and supply voltages for this type of application?

Thanks in advance for any suggestions!

Cheers
Graeme

No suggestions guys? Just looking for a little guidance on what supply voltage I should be using for a job like this, and therefore what drives would be a good bet. Any pointers would be much appreciated!

Well, since you asked...

I would be very tempted to go the obvious route of AM882 (EM806 if you're feeling posh) plus the usual 45V toroidal-based linear power supply giving around 68V (off-load, anyway). Lower voltage power supplies won't save much money, and you can always turn max stepper current down to minimise heating if you don't need the torque. Frankly, I'm not too sure what other decent driver choices there are. Gecko? Over-priced and under-specced compared with the Leadshine drivers. Then it's down to the TB66xx kind of thing, which I've used happily off a 12V supply but which probably aren't fit for anything serious.

My philosophy here is to pay just a little bit more; in the long run you spend less by spending slightly more to start with than trying to minimise costs and wasting what you did spend when you replace it with the right kit. Different if you are manufacturing many-off. I remember a quote from somewhere along the lines of, "Pay a little too much for a tool and you forget the cost the first time you use it. Pay too little and you regret it every time you use it."

YMMV!

Hi Neale,

And you may well be right that this would be the best way forwards! My philosophy for most things is to buy well and buy once.

I suppose I was waiting for someone who has done similar mini mill conversions to come along and say that 68v is overkill for such a machine, and that you would be better using a decent 50v drive - like an EM503 - and a matching 45v PSU. Or whatever. It could save a few of those £s without affecting the performance.

But maybe the kit that is well proven for routers is equally suited to a mini mill? A well trodden path that simply works well. I have to say that the price difference between the EM503 and the EM806 (as examples) belies the much increased current and voltage capabilities of the higher spec drive....

Plus one on the AM882 route I use them on my mill, lathe and router all on 68V

Ultimately it depends on how much performance you're hoping for.

Higher voltage will let you run faster, which on a ballscrew equipped mill of X2 size, probably wouldn't give you much performance gain, as the steppers wouldn't get up to high speed that often.

However, as you'll be using trapezoidal screws, which will have a smaller pitch, and be less efficient, you'll want to maximise torque, and most likely run at higher motor speeds. Which means higher voltage drives could be quite beneficial, but can you justify the extra cost?

Mmm, as ever there is no right answer I guess! What I'm hearing is that AM882's will undoubtedly do the job on both mills, but is it worth the outlay. On the ballscrew mill, they probably wouldn't be used to their potential, and for the trapezoidal mill they may just be overkill for a "cheap" implementation - albeit their abilities may be useful.

So, what would be the next step down, voltage and drive wise? Given that as a data point will allow me to price it up and decide if the saving is worth it?

Hi Neale,

I work for Charter Controls who are the UK importers for Geckodrive in the USA. I don't know if you have seen any of my previous posts but as a member of this forum you can use a discount code on our website. If you enter coupon code "mycncuk" at checkout you will get 15% off the list price. You can see the items and what we have in stock here: https://charter-controls.com/manufacturer/geckodrive

If there is anything else I can help with, please let me know.

Regards
Murray Greenhill
Attachment 21346

Some of this depends on motor type 4 or 8 wire. With 4 wire your stuck to how motors are wound at factory, often series. 8 wire can choose which.

My choice for small Mill would be to go with AM882 with 60-65vdc and wire motors in series. This will give you more torque down low and seen as you won't be going fast there'll still be plenty of torque left up high. The reason you need 60-65V is because series requires more voltage to get decent speed.

Router then you'd wire motors parallel because want more RPM and torque to run higher up the rpm range. This does come at the cost of losing little lower down.! . . . Can't have cake and eat it I'm afraid.:dejection:

The AM882 will offer more motor choices and upgrade potential if required. There advanced Resonance handling and smoothness are worth paying that little more for IMO.

That's a really interesting take there, Jazz. All the motors we are using are eight wire, so we do have complete flexibility. And that means the PSU for the mill only needs to supply half the current that an equivalent router one might - say 4A at your 65v, allowing for a small saving in cost, but a larger saving in space. I am coming round to the benefits of the AM882 even for this application - future proofing certainly - as well as gaining the advanced resonance handling etc. I think that must be the way forwards.

So now I have to take a deep breath and start considering my first large value order into China - six drives. Seems no alternative for the AM882. Anyone have any idea why it's not available in the UK, especially since it is the stepper drive of choice on this forum?

Just note that if motors are 2A then you'll need to configure current using the AM882 Tuning software as the DIP switch lowest setting is 2.8A. The Tuning software allows setting from 0.5A upto 8A in 0.1 increments.
This will mean you'll require RS232 cable (serial)

Think the reason why not in UK anymore is can't compete with China prices. Don't worry about buying from china I've bough 100s never had issue. But be aware you'll pay VAT and Shipping admin fee around £10-15. If you ask seller they will put low price on paper work which will help with vat.

Cheers Jazz - good tip on the current setting, as it will be in the order of 2A for series connected I think.

Good info also on the Chinese supply. Are there any "well proven" Chinese suppliers you could name? Or do you go different each time?