Re: I am Lookig for stepper??

Chris,

I have always assumed a 95% efficiency for a ball screw and a 35% to
50% efficiency for an ACME thread. Either way that is still way more
enough to bend and break things (maybe I should just stick to circuit
design where I'm on firmer ground):-)

Mariss

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
>
> Mariss wrote:
>
> > Consider this. The force (in lbs) a motor generates is:
> >
> > Lbs = (in-oz times 2pi times TPI) / 16
> >
> > or:
> >
> > (384 times 6.28 times 20) / 16 = 3,014 lbs.
> >
> > Seems to me this is just a bit of over-kill. If you mounted the
axis
> > vertically you could lift your average 4-door car with it.
>
> The thing is that this is a flawed analysis, as it neglects the poor
> efficiency of a sliding contact screw such as used in the sherline.
> Because of this, you don't get to take advantage of the fine pitch
of
> the screw - you get no more force out of it than you would out of a
> much coarser screw. 384 oz-in is overkill for this machine, but 150
> oz-in is just about what you need to get top performance from it.
> This oversimplified calculation would imply that even the 150 oz-in
> motor would generate a sherline-bending 1000 lbs of force - in
> practice, it won't even come close to that, but it will have just
> about enough to torque left to reliably overcome the friction in the
> system when the torque loss at high speed is taking into account.
>
> Chris Stratton