RE: [CAD_CAM_EDM_DRO] Sizing servo motors for BP size mill

I am running G320 drives on a Bridgeport series II with about the same setup
as you are listing below. I have no idea what the torque is on the servo
motors I am using as they are E-Bay specials and not marked with a torque
rating. They are roughly NEMA 42 diameter and about 8" long on the X and Y
motor and about 10" on the Z not including the shafts or the encoders. They
are 90 vdc rated (one of the few things marked on them). The X and Y are off
a large laser cutting table and the Z is off a Hurco mill. I am very happy
with the performance.

Regarding the waviness you can pretty much figure it out by calculating the
movement per step for what you have now and what it will be on the servos.
For the G320 a step is 1 encoder pulse which is 4X the line count of the
encoder. So, a 250 line encoder will have 1000 steps per revolution. If you
steppers are half step than the waviness will be less than 1/2 of what you
have now. If you have full step steppers it will be 1/5 what you have now. I
would caution you about going to too high a resolution as your required
steps per second rapidly get so high the computer may have a hard time
putting out a fast enough pulse rate. Depends upon the software you use and
how fast you go. On Bridgett I am set at 120 ipm for X and Y and that
requires 20000 steps per second.

If your goal is resolution you will not gain anything by using G340s instead
of G320s. To get the most resolution you need to run them in 1X mode and
that is exactly the same as what a G320 is. So there, I just saved you
$60.00

Hope this helps,
Tim
[Denver, CO]

> -----Original Message-----
>
>
> I am looking at possibly converting my Ahha mill to run brush servo
> motors using the Gecko 340 drives. Ball screws are .200 pitch, will run
> 2:1 belt reduction.
> Current stepper motors are older Sigma and I was told they are rated for
> 840 oz/in at 10 amps. They are presently running at 7.4 amps via
> Compumotor drivers.
>
> What in/lb range servo motors should I be looking for to offer a modest
> increase over what I have now?
> Also, a significant reason for looking into this is I do commercial
> work. When interpolating radii and holes, as well as shallow angle
> tapers, I get a visibly wavy cut. We're not taking much here. It's an
> aesthetics issue here, there are just classes of work where this is not
> acceptable and thus I lose out on the work.
> Will the Gecko drivers with a high resolution encoder improve upon this
> finish?
> (not looking for perfection, just a significant improvement)
>
> Thanks,
>
> Jon
>
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