Re: [CAD_CAM_EDM_DRO] Z axis servo reduction gear

Les, just for the record I've been given a totally different equation
to calculate force from a screw.
Force= [Torque x 2 x Pi x Eff]/ Srew lead
F=lbs
T= in/lbs
Eff =x/100 or [0.xx]
Lead=inches

In that instance w/ a delrin nut I'd think it would be at lease 30% efficent
50oz-in = 3.13 lb-in

f=[3.13 x 2 x pi x 0.3] / 0.10
f=60lbs

Sorry to cloud the numbers

Just thought I'd throw that out there anyway.

Jarrett J

> 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
> >
>
>
>
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