RE: motor sizing vertical slide EDM

Hello All:

Graham:
thanks, To get fine reaction ( measurable motion when the smallest change in
control voltage is detected), Hurco used large gear reduction ( meaning the
motor kept moving more ) and fine pitch lead screw ( smaller motion but
easily discernable by the control system). Good idea, my AGie AB uses 5000
rpm dc motor with 5000:1 double worm reduction and 2mm pitch lead screws.
This also allow the motor to stay out of the 'dead' area , respond to very
small changes in control voltage, and move very small amounts.(max velocity
is 2mm/minute! but can cut with .01"x.01" tools )

Mariss:
thanks,
1) yes the reversals create near 3500 lbs force, didnt know that was 5G. That
general idea was why I was opting for 1.5" dia ballscrew, maybe it oughta be
bigger!
1a) reasonable systems react at 40ms ( acceleration times that are 8x of what
you stated, so it's true that better reaction will be had with the more
powerful motors). The reversal is misleading tho, at the beginning of the
reversal, the velocity will be near 0 but 'forward' ( EDM is slow but quick,
sort of 'nervous').
1b) I'm sure I'll be buried inside the accelration ramp time during my
reaction, and wont arrive at the full velocity. The reason for the outlandish
desired velocity is to decrease this time. Rather than the slow 'rapids' of
most machines ( a result of good control at low velocity sacrificing top
velocity ) I opt for higher rapid rates only to increase the reaction speed
at low velocity ( this gets me the 'quick' ).

re: question
Does the use of the high velocity to get 'quick' make sense? is it valid?
Recent experiment showed systems with nasty old generators ran sweet when the
mechanics and motors were changed ( 150W dc brushed to 400 watt Yaskawa ).
Just this change contributed to the control loop enough so the system
suddenly competed with new equipment.
2) that's a lot of calcs, I gotta study ;-) thanks

Marcus:
Anytime the EDM control loop handles the gap position better, it runs better.
It isnt very noticeable at 'rough' but is always noticable at 'finish' ( what
rough and finish are to different disciplines varies a lot ). But systems
always respond better when quicker and able to resolve finer position.
I know about crawling: imagine systems with 3 meters of X travel and rack
type tool changers! The operators avoid changing tools!
I plan on servo but see a great advantage in using steppers on the contol
side. It's just that steppers of that power are more expensive and hot. I
could use the amp styles that take servos with rotary encoders and 'step'
them.
re: linear motors: yes the street buzz is that Sodick Inova got near 5G on
those 'jumps'. I've gotten near 2.5 with the Yaskawa setup mentioned above,
and suddenly could cut 'no flush' with simple generators. Quicker is better!
re: mother of all rams: Nope, several machines have much larger. A SIP in
Elmhurst Illinois was made for steel on steel, and the ram face was 1.5 meter
square, It was hydraulic, didnt move as fast as we said earlier, but way way
over 700lbs.Also many of the older Nassovia's ( bought by Charmille, bought
by Geo Fischer) were much bigger. I've got 350 lbs of platen based fixturing
to begin with, and also have a 300 lbs slide ( the motor sees near 700
static ).I can actually ignore the weight of the graphite electrode! It
doesnt change the equations enuf!
The ability to burn deep skinny ribs can be viewed as an overall performance
test of your system. The systems that cant cut .020" X x 1.0"Y x 2.0"Z will
be having trouble with simpler forms, and the better system wont. With the
new Yaskawas, I cut 10mm deep with a 250um wire, no spin, no flush, just
jump! Quick is good, stiff is neccesary.
In this control type, the ability to cut small deep and fine are 'poles' in
the equation. Quicker expands the distance between the poles, and makes the
system more 'robust'.

Thanks guys!
I think that I've gone overkill, but not by much. I doubt I'll reduce
anything till I test it on a real system. Get pragmatic, get dirty, then
reduce.

regards
TomP