I know, another "Help me Pick a Stepper" thread...

I've done tons of research on steppers and I've been familiar with them for a long while but I'm stuck at deciding which ones to buy. I've got a 3040 CNC frame coming and want to outfit it with electronics to learn with but that will also be suitable for a larger and better machine that I can build in the future. I'll be using a 2.2kW water cooled spindle and a sensorless vector drive from Hitachi. I'm using a TinyG for control (for now) since it's easy and pretty cheap. I'll re-purpose it in a 4 axis machine down the road.

But for now, I'm limited to 2.8-ish amps/phase and 30 volt motors. I know the relationships between voltage, current and inductance (I think) but don't know how they apply to a CNC router used mainly for wood and plastic but hopefully also aluminum so I can make parts for my second, larger router. What's most valuable? Torque? Low inductance for quick travel? Voltage for speed? I know you can't have all three but which should I be concerned most with in this application? The 3040 has ballscrews so it should move easily with low torque but will I need more torque when cutting aluminum? I'm not super concerned with the time to complete a job but will I need more speed in order to machine wood and plastic?

Does anyone want to just tell me which stepper to get? lol

Thanks!

P.S. Anyone know what NEMA size the generic 3040 frame uses? I can't seem to find any reliable info on that...

Chjade84,

The majority of 30 series routers are equipped with nema 23 steppers.

If you were planning on repurposing the motors on a larger machine in the future the 425 ounce Automation Technologies model would be a good choice.

See link below:

NEMA23 425oz/in 2.8A Stepper Motor

Welcome to the Zone,

Jeff...

I actually have that one bookmarked! :)

My only concern was would it be able to move quick enough with just 30 volts?

Thanks for the welcome, glad to be here!

The short answer would be "no". With such high inductance (6.8 mh, except if you run it in series, which boosts it to 27.2) it would need a lot of voltage to do anything but crawl along. Using the formula 32 * 2.6 (square root of 6.8) = 83.4v gives you the maximum voltage; the optimum voltage is only a little bit less. Look for a motor with less inductance.

So I need an inductance of around 1 mh... What about torque? What's an acceptable torque figure for CNC in wood and even light aluminum? I don't need to go fast on the rare cases where I need to do aluminum but I would like a good surface finish and to run with a proper chip load.

chjade84,

If you are limited to 30 volts this motor would be better however it needs 3.5 amps to perform optimally.

NEMA23 381oz/in 3.5A Dual Shaft Stepper Motor KL23H2100-35-4B | Automation Technology Inc

or this one:

Stepper Motors | HobbyCNC

#23-205-DS8 285oz-in bipolar rating, 205oz-in unipolar rating. 3v, 3A, 200 S/R, 2.2mH, Size #23, Dual Shaft, 8 wire faster than the 305’s. Good all around choice.
NEW LOWER PRICE!



Jeff...

Chjade84,

Your best bet is to revise your stepper driver specs and power supply then you can choose motors that will perform much better.

Jeff...

Unfortunately I'm limited to 3A and 30V - technically it's only 2.5A but I'm told you can run to 3A with active cooling which isn't a problem. Maybe I just have to go with smaller ~175oz-in motors and wait to get nice motors until I get a proper driver. I just have no idea what power is adequate for a smaller CNC like this. 50oz-in? 100? 300? I also won't have my frame until Monday so I can't measure the torque required to move the axis yet either. It can't be much though, with ballscrews and bearings...

My specs are:
<= 30V
<= 2.8-3A
0-? in/min (what's needed for wood as well as aluminum?)
Torque: ?

Chjade84,

If it were me I would purchase the KL23H2100-35-4A
381 oz In. Hybrid Motor
1.8° /200 Steps Per Rev.
3.5 Amps Current Per Phase
Inductance 2.8 mH
4-wire Bi-polar,
NEMA 23 Frame

Run them at the reduced current you have available, that way you will not need to replace the motors when you upgrade later.

They will perform almost like a 280 ounce motor with the current you have available.

Jeff...

Oh, duh! You don't NEED to run them at full current... I... I should know that... lol They can only pull the current you supply.

Thank you. :)

This page may help you:
techref.massmind.org/techref/io/stepper/estimate.htm