Re: Servo or sterpper motors. on small mill?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@...> wrote:

>
> If both motor types are understood, and the how, why and where to

apply their performance characteristics, either are good candidates.

>
> To simply say one is "better" than the other, is simply wrong.
>
> Ron

If both motor types are understood, AND (huge AND) the machine will
benifit greatly from one and work poorly on the other, there is a
better unit.

I have a PCB drilling and etching machine and the process of
mechanically etching is done at about 20 inches per minute with a
25,000 RPM spindle. Can you say any motor is more accurate to move a
10 pound gantry around at 20 inches per minute ? I cannot.

I can say that for $50.00, using a stepper, I can get the same results
from a stepper. A servo would cost way more and it would not offer one
iota of performance improvement.

on that machine, the stepper is better because it is simpler and cost
less and offers the exact same result.

I spoke to a man who has a laser table, it moves to better than
0.0001" resolution at over 1,200 inches per minute and the gantry
weighs some 500 pounds. I don't think there is a stepper in the
world that you can afford that could handle that task. There IS a
better motor.

Mariss has said many times that at around 200 watts and below, the
stepper is usually a 'better' choice and above 300 watts a servo is
usually a better choice.

On smaller machines steppers offer more power at the cutting speeds
and less at the rapids speeds than servo's. simple mechanics.

A stepper can be $30.00 for a decent size and $30 for a high quality
driver or about $60 per channel

A servo cannot beat that price, and does not offer better performance.

On a medium duty machine the performance curves cross to where neither
has a clear advantage, and as the machines become more specific, one
becomes better than the other.

I think that the majority of Bridgeport knee mills in this group are
run with servo's, but I know of at least 2 that are stepper driven,
and those steppers are every bit as good. I think there are dozens of
people who tried to used steppers and failed for one reason or
another. On a Bridgeport both can work, Steppers need to be applied
very precicesly, servos have way more room for error. So in that
application, I think we can safely say that servo's are better.


If you understand the motors and the application, I submit one can say
one is better for an application.

Dave