Driver & Driven

**manofgresley** · 15-09-2013

Hi

I should know the answer to this, and i think i do, i just need reassuring.

I have a 3Nm, Nema 23 motor, i am going to use to power my Z axis on my milling machine, i intend to use a toothed belt & pulleys, my question is this, should the DRIVER pully (ie, attached to motor shaft) be LARGER or SMALLER the the pulley being DRIVEN (ie attached to Z axis Leadscrew)

Regards

Ray

**JAZZCNC** · 15-09-2013

Well really that depends on what your after.? If your wanting higher speeds then larger pulley on driver, this will come at the cost of torque.
If have a fast motor and are wanting slower speeds with more torque then smaller on the driver.

I think you'll be looking to increase torque so go small on driver.

**birchy** · 15-09-2013

It all depends what gear ratios you want to achieve. Generally speaking, a direct drive system would use either Oldham Couplings or drive pulleys of the same diameter. For increased torque and slower speed, you need to use a smaller pulley on the motor (or a larger pulley on the leadscrew).

Incidentally, notice I linked to HTD5 pulleys above? I bought T5 pulleys and then discovered the belts are pretty expensive. The HTD5 pulleys are (apparently) a better choice as they will have less backlash and are easier/cheaper to get hold of.

**manofgresley** · 15-09-2013

Hi again

My X & Y axis are direct drive, using Oldham Couplings, the Milling head, gearbox & motor are quiet heavy, i am not to bothered how fast the Z axis travels, i am more interested in relieving some work on the motor, thats why i thought of using timing belt instead of direct drive, should i use 2:1 or 3:1 Should this be Driver to Driven or Driven to Driver?

Regards

Ray

**JAZZCNC** · 15-09-2013

I'd go 3:1 with small pulley on stepper.

If you want to relieve some stress on the motor then use some form of counter balance, either weights or gas struts.

**manofgresley** · 15-09-2013

Hi All

Again many thanks, believe it or not, that's just what i was thinking of, honest, just had one of those age moments that lasted a couple of hours.

Ray

**birchy** · 15-09-2013

I have pulleys for 3:1 on my Z-axis as well!

However, this interesting response was a reply when I asked the very same question: http://www.mycncuk.com/forums/faqs-p...html#post47446

**manofgresley** · 16-09-2013

Thanks Birchy.

I had already decided on a key way driven pulley on the Z axis Leadscrew, has the existing shaft has one in, so i will utilise the existing keyway.

Regards

Ray