Re: [CAD_CAM_EDM_DRO] Re: Calculating stepper power

Hi All:
The project is to determine the feasibility of changing the hydraulic
servovalve driven ram on my sinker EDM for stepper control.
I want to do this because the hydraulic system is noisy, hot, and won't hold
position perfectly when it's locked.

Here's what the machine is doing now:
Rapid descent or rise with the servovalve fully open...50 IPM
Full ram stroke stop to stop...6"
Ram weight with orbiter and chuck...18 lb.
Heaviest electrode used to date...3 lb
Current electrode capacity....300 lb (it's hydraulic!!)
Unconstrained ram descent rate while set to burn...3.6 IPM
Ram descent rate while burning...depends on gap voltage, but very slow.
Ram speed for rapid cycling (pulse flushing) 3.6 IPM
Typical pulse flushing stroke....0.020"
Rapid rate (used for homing ) on the Gromax orbiter... 1.6 IPM (This is a
stepper driven device that allows me to do sideways burns...very cool).
Typical spark gap....0.0015" to 0.0005" for the kinds of burns I do.
Permissible spark gap variance from commanded....I'm guessing 10% up or down

I have a very nice Hiwin screw with preloaded ballnut that's 0.2" pitch.
I have some space constraints in the machine frame, that limit what I can
do, so I've decided to bolt the end of the screw to the ram and rotate the
nut.

Here's where I'm now at...please give me a kick if I'm out to lunch here:

10:1 reduction using compound timing belt drive from the stepper to the
ballnut.
A double stack NEMA 23 frame stepper and half step or 10X microstepping
drive. (biggest honkin' stepper I can buy that's NEMA 23!!!)
This gives me the following, on a 200 step motor:

Full step increment...0.0001"
(This theoretically gives me my target positioning resolution with half
stepping, and maybe a bit better with 10X microstepping.)

1.6 IPM feedrate...80 RPM on the stepper
3.6 IPM feedrate....180 RPM on the stepper
50 IPM rapid rate...2500 RPM on the stepper. I can live with half of this if
necessary!!

For control I was planning to do the following:
Shamelessly bug my friends, some of whom know infinitely more about this
than I ever will (I'm electronically challenged)
Borrow the circuit design that's already working well in the Gromax orbiter.
Cry and beg for help on the list when I get totally stuck!
I appreciate any and all feedback...the alternative is dropping muchos
dineros on a proper CNC sinker, but I hate to commit that much money, even
for a used machine.
Cheers

Marcus