View Full Version : Please help me with step motor choice.

07-06-2017, 12:59 PM
Hello, I Am currently converting an emco 120 lathe.
It has a Chinese cnc controller, simalar to fanuc system.

I need to buy a stepper/driver combination for the lathe but I need some help choosing the best route.

The axis force from the brochure states 10n force.
Then ball screws are 5mm pitch, and the motor ball screw has a 2:1 ratio where the motor turns twice for every rev of the ball screw.
The machine max rapid speed was 2000mm/min
So I guess if I've calculated correctly, the motor would turn at 800 rpm at max rapid. I have no clue what the motor torque should be?

So my question is should I buy nema 34 4.5nm closed loop stepper/driver?
Or should I buy nema 34 8.7nm open loop steppers with dsp drivers?
Or should I buy 4.5nm open loop steppers/dsp drives, and close the loop to my controller using an encoder?
Or just simple and cheap 4.5nm open loop system?

These options are all I can physically fit in the space available.
Ideally I'd like to increase the rapids a little without compromising performance or reliability.

Many thanks

08-06-2017, 12:34 AM
Nema 24s will perform far better than 34s for that size of machine.

Combine with good drives and power supply, and you'll get better performance than 34s.

Lee Roberts
08-06-2017, 11:02 AM
Toolman there is also quite a few sticky threads in the Stepper and Servo (http://www.mycncuk.com/forums/80-Stepper-Servo-Motors) forum if you would like a better understanding and some more reading.

Link: http://www.mycncuk.com/forums/80-Stepper-Servo-Motors

As said above, you typically cant go wrong for most machines by using Nema23's in the 3Nm flavour, basically try and find the versions with the lowest inductance and the cheapest price, right now that is the ones from CNC4YOU listed here:

Link: https://www.cnc4you.co.uk/Stepper-Motor/Nema23-3.1Nm

3 of these with p&p is still the better option than going via China and importing some, they continue to hold their price well at our purchase level.

Edit: Lee, the way you can increase the rapids is to use higher voltage drivers, look at units like the EM806 (http://www.ebay.co.uk/itm/322520323977) or the AM882 (http://www.ebay.co.uk/itm/330782929553), using software you can fine tune these drives once fitted as they are digital.

Good Luck!