Re: [CAD_CAM_EDM_DRO] Z axis servo reduction gear

Assuming the screw is 100% efficient the formula for thrust is:
torque * (2 * pi) * TPI
2 * pi is near enough 6 for our purposes.
So the thrust available at the motor's continuous rated torque is:
50 * 6 * 10 = 3000 oz or 187 lbs.

However an Acme screw is only around 20 - 30% efficient. Assume worst
case so the available thrust is more like 37 lbs.

You can't safely use peak torque but it is usually safe to use 3 times
continuous torque for short times so the peak available thrust is in the
region of 110 lbs.

So - theoretically direct drive should work. However a good zero
backlash coupling will cost pretty much the same as a couple of pulleys
and a toothed belt so I would probably go for a belt. That way you can
change the ratio if for some reason you find it is under powered. Don't
directly bolt the shaft to the motor. You must have some sort of
flexible coupling otherwise you will probably overload the motor bearings.

Les

dcassyc1 wrote:

> Hello,
> I'm trying to decide whether I need a speed reduction on my Z axis router carriage design. The Z axis is powered by a nema23 servo motor from homeshopcnc,
> http://www.homeshopcnc.com/servo2.html
> and is rated 50 oz in continuous and 350 oz in peak torque. The acme lead screw is 10 tpi V thread and the nut is Delrin AF, the bearings are IGUS dry lin on 3/4 inch shafts. I plan on using the homeshopcnc 3 hp spindle at 21 pounds, so I think the carriage weight will come in at around 30 pounds total by the time the spindle is mounted in a clamp.
> Is it possible to drive the lead screw directly off the motor with no reduction or would I be better off coupling the servo to the screw through a timing belt reduction setup to increase the torque and reduce the load on the motor somewhat? If it's obvious that I need a reduction what sort of ratio should I aim for?
> Thanks
> Denis
>