Re: [CAD_CAM_EDM_DRO] Re: Reduction

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