Re: [CAD_CAM_EDM_DRO] RE: motor sizing vertical slide EDM

Hi Tom:
Sounds like you've got a pretty comprehensive understanding of the whole
process and are clear on your needs.
One thing I'm having difficulty with though....how will you reconcile the
mutually antagonistic goals of high speed versus fine resolution.
I'm facing this same issue with a much simpler problem (CNC conversion of an
engine lathe).
Finding a workable balance for my problem is a path well-trodden by many
already, and I can follow in those footsteps, but you're accepting a far
more expensive risk if you miscalculate.
Fine pitch leadscrew plus high rapid rates equals insane screw or ballnut
rotation speeds (sounds like servo to me) together with the corresponding
acceleration, screw whip, and thermal growth issues.
Coarse pitch leadscrew to reduce motor speed equals poorer resolution and a
far higher workload for the drivetrain components.
Seems to me that the design choices of Hurco opted for resolution over
speed, and Sodick had to break new ground to tilt the equation the other way
successfully.
Are you planning to do a sophisticated build with everything formally
engineered, including thermal growth management?
I don't see how you can really avoid it, given your stated goals.
If this is going to be a high end project, have you considered using the new
SKF roller screw instead of a conventional ballscrew?
There are some significant advantages:
First, you can get much finer pitches with hellaciously high load ratings,
so you can often eliminate having to gear the screw down.
Second, you can manage high cyclic loads far better, and for a lot longer
before failure of the screw.(much larger contact area of nut to screw)
Third, to the best of my knowledge, you can manage high speeds better
(larger root diameter for a given screw OD therefore better screw stiffness
at high speeds)
The only downside is that they carry a correspondingly audacious price tag.
Check them out on the SKF website...they're worth a look at least.
www.skf.com/portal/skf_ca/home/products?contentId=150201&lang=en
Cheers

Marcus