Here's the background. Having bought a biggish mill (Amadeal VM32L) I find I really would like a power feed. I knew that, of course before buying it, but manufacturers power feeds are not cheap. In addition I would like to consider CNCing this machine at some point and thought a stepper motor would be a good approach.

Also as a software chap, I quite fancied the coding challenge – I've already built a CNC like system for my micromill.

Finally, I've been overspending my engineering budget recently so cost is a factor to avoid a swift blow from the good lady.

I'm struggling with the maths. I found various places where I could calculate the power of the motor I needed, but came away more confused than not.

The table is around 840×210 and I calculated the mass at around 60kg with a 20kg vice on it making 80kG.

The most useful site I found was this which had a calculator on it (a spreadsheet).

This reckoned I needed a 12Nm motor. Which is big and expensive and needs big power supply, drive and so on.

I'd been hoping that the PSUs and drives I already had (15A 24V PSU and 3.5A 6600) would do the trick.

I then started looking at DC motors. In particular cordless drill motors. I have one that I took apart eariler ( a drill), though the gearing is missing some cogs.

I found that I could make the table whizz along good and proper by attaching my 18V cordless drill to to the leadscrew. So enough power and controllers seem cheapish.

However, I was still confused about how much power I actually needed, so I build myself a poor man's dynamometer (if that's the right word.

This consists of a pulley on the X-Axis leadscrew, a bit of string and a luggage weigher.

the pulley radius is about 20mm.

I found I could move the table at milling speed with about 5kG force.

I then took a 50mm facemill and cut a 1mm deep channel in some mild steel. the first time round I'd set the cutting speed too low (450rpm) and it needed 7/8 kg Force. The second time at 800 rpm it only took 5/6kg again.

I think that's 50 Newtons at 2cm which is 1 N.m well shy of what the estimates worked out. Clearly a fast traverse would require more (I shall experiment).

There seems to be a wide range of views of what sort and power of motor is needed for this and I'm struggling to make sense of it.

What I would like is to use a 3./ 3.5 A stepper such as this claiming 3Nm, but I fear that it will struggle. Can you confirm my fears.

On the DC motor side, can I control the speed well enough? I would think so though I'm still left with power requirements. The motor from my (dismantled) drill claims to take 380A at stall speed according to a spec sheet I found, so power becomes a challenge. Specically it looks like I need 30 or 40 A at least at 18V.

I did think of running it off the original battery but with the charger on all the time. Thus the battery acting more like a capacitor.

I'm sorry for all this dribble, but any clarity you can provide would be most welcome!

Iain

Thanks, All.

Martin, I do want high speeds – for return and moving from one end of the table to the other for jobs needing different clamps. I can be quite patient when need be, but I don't relish winding a wheel 200 times just to move the damned table!

Thanks Steve. I think my drill motor idea may be overkill torque-wise, though it does have some interesting challenges for reducing the speed and may give me a chance to use my gear cutters.

Thanks, Jason. One of the complications appears to be that it's not just the torque, but how it behaves electrically. The sources mentioned consider inductance and voltage – the higher the induction, the higher the voltage to run at a given (higher) speed. And, as above, I'm keen to get a fast return.

As far as power is concerned, my preference is for carbide tools on the mill, though they are expensive when you break them. I've not really tried to see how much grunt I can get out of the mill, but I should like to be able to run hard if I need to. Though, again for occasionally deep cuts, I can run by hand if I need to.

I suspect my sweet spot is in the 5 – 8 Nm range for a stepper. Perhaps I should just save my pennies

Iain

OK. I've had enough of dithering. I'm going to treat this as an experiment and be prepared to throw it away.

I've already got a 24v 15A power supply and some 3.5/4A drives, so what I'm going to do is to buy this which gives me a £27.00 introduction to the art and see it it works. God knows why it's sold from Austria, but that's the modern world.

If it's not powerful enough I'll change the gearing.

I can get more speed out of it (I gather) by increasing the voltage which is a relatively cheap thing to do.

If I want to go full CNC later then this is an investment I can comfortable discard.

Gentlemen of the wiper motor variety. I'm afraid that my digital background has betrayed me. I want something I can control and £27 quid seems a reasonable investment.

I will report back once the motor has arrived and I've assembled the bits and build the controller. Hmm. Don't start any short novels!

As always, thanks for all the helpful input.

Iain

Just a quick vaguely related question – I'm planning to connect the motor and lead screw with a timing belt. There are a vast range of options.

Is 10mm width sufficiently strong? Is 5mm pitch too big – should I try for 2mm?

Iain