Re: Reduction

Jon,

thanks for the explanation. Those "unstated provisos" can really
catch you off guard when you're just starting out. I sure don't
have an ideal voltage source in my basement. :)

From what you've said, I think I'll go with direct-drive to the
leadscrew. At least for the short term. If I find that my motors
are straining, then I can always gear them down with some pullies
later. Are there any compelling reasons not to do this?

...And... I can use my direct-drive CNC to machine the pully
assemblies if I need to. ;)

I like your idea of mounting the encoders on the leadscrew rather
than on the motor for a pully drive system. (In another thread) In
fact, I was considering that option myself. Is it difficult to get
working correctly in terms of alignment and tweaking?

Thanks again for setting me straight.

Jake

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> jbordens wrote:
>
> > > > 45IPM is too fast, of course. I'll probably be dealing
mostly
> > with
> > > > aluminum, plastic, and in some rare instances, steel.
> > >
> > > 45 IPM is to FAST? Really? How about rapid travers, where
you are
> > going
> > > from one place to another? On a Sherline, 45 IPM might be
fine,
> > but on a
> > > larger machine, that may be an annoyance. Why will you only
get 45
> > IPM?
> >
> > My leadscrew is 10TPI. I was figuring for the point at which the
> > motor is at peak power output (1/2 the stall force, 300-in-oz at
450
> > RPMs) Unloaded, the motor is 900RPMs which would be 90IPM.
> >
> > Somewhere in the back of my mind I'm thinking like this, please
tell
> > me if this thinking is flawed. I'm pretty sure it is...:
> >
> > Peak output (watts) is at 450 RPMs @ 300-in-oz. When cutting a
hard
> > material like steel, I'll probably want my motors to be
operating in
> > this range. Hence, I should gear the reduction so that the most
> > power is being transmitted to the table when cutting at steel-
speeds.
> >
> > Not sure if that makes any sense...
>
> You've been listening to Mariss too much, without understanding
some of
> the unstated provisos in his comments. Don't worry about peak
output.
> That only applies to motors run off constant voltage supplies. A
servo motor
> is run from a servo amp, which applies voltage and current as
needed to
> accomplish the desired task. The motor can deliver rated torque
up to
> a speed where the servo amp can no longer supply sufficient
voltage.
> So, you can get full torque up to 90 IPM, if your power supply has
enough
> voltage for that. Also, servo motor voltages are not hard and
fast limits.
> You'll suffer no harm running them up to, say, 25% above rated
voltage,
> assuming that this will be only for momentary rapid feed moves.
The peak
> current limit IS a hard limit, the magnets will be fried if you
exceed that.
>
> Rapid traverse is generally a low force operation, although there
is force
> involved for acceleration. So, you'll have no problem doing 90 IPM
> rapids. Unless you use a router motor for cutting soft materials,
you
> won't ever be machining at these feed rates, anyway.
>
> I have rapid feeds up to 100 or 120 IPM with much smaller motors
than
> yours.
>
> Jon