Re: Smaller machine stepper motor speeds and resolution

Funny how calculations can take us into the world of the unworkable.

Yes, 60tpi would offer a great speed/power ratio. and be in the
meaty part of the stepper power band, but (hate that but) have you
thought about the thread ? if a ball screw was used and the thread
was set to have a quarter ball width for support, your 60 then is a
inch divided by 75 . One unit for the ball width (60) and one quarter
for the web of the thread.

that results in a precision ground thread with a web of 0.013".

So with the power of the NEMA23, you might rip the threads off in
short order.

ACME ? I'm not sure of the formula but supposing it is half nut and
half bolt, then each bolt thread would equal half of the inch, that
would be 60 up and 60 down. divide 1 inch by 120 and each thread is
just slightly over 8 thou. A thick piece of copy paper is only
about 6 thou so this is one thin thread !

As a friend used to say, "Don't force it, get a bigger hammer"


Dave








--- In CAD_CAM_EDM_DRO@y..., "stevenson_engineers" <machines@n...>
wrote:

> --- In CAD_CAM_EDM_DRO@y..., Mark Taft <mark.taft@m...> wrote:
> > HI everyone,
> >
> > I am converting a small mill to CNC and have been considering
> >stepper motor
> > speed and resolution of the z feed.
> >
> > Its obviously a compromise using steppers, so you need to gear

the

> >feed at a
> > rate which is practical ( fast as possible) while not loosing
> >accuracy
> > resolution or losing steps ( being under powered).
> >
> > I have studied the stepper motor specs for the smaller 34 and 23
> >sized
> > motors.
> > They seem to get most torque at about 900 - 1000 Hz..
> >
> > With a 200 step motor this works out at about 4-5 Rps (revs per
> >second) ,
> >
> > using a lead screw of 60 tpi and a 4 inch travel ( maximum) it
> >takes about
> > 60 seconds.
> >
> > I am picking a 60 tpi screw for increased torque.
> >
> Don't bother.
> You are wasting your time with a screw this fine. A micrometer is

40

> tpi. Imagine driving that up and down all day with a motor and
> expecting it to last and be accurate.
> If you are worried about torque just pick the next size up motor.
>
> John S.