Re: [CAD_CAM_EDM_DRO] Re: Servo motor selection

jbordens wrote:

> Jon,
>
> Thanks for the reply. Now for the question: what about acme screws
> at 10 threads per inch? Do you feel that I should preform a ball-
> screw retrofit before I go on to the CNC?

Backlash can't be compensated for in software, except for positioning.
But, you can't get smooth motion with reversals when backlash is
present. This is the most important reason for ballscrews.

> I know there are backlash issues and such, but for the short term I
> think that backlash correction should be suffcient to help me. I
> eventually want to do the ballscrew conversion anyway, but the CNC
> project is really what I'm itching for.
>
> With the added friction of acme screws vs. ball screws, is this 600-
> peak, 50oz-in/amp still sufficient? I don't know the pitch diameter
> so its hard for me to calculate the efficiency... Any "rules of
> thumb"?

Well, I'm sure it will work. but, you'll have bumps at the places where
an axis has to turn around, as when milling a circular hole of arbitrary
size. So, you lose some of the advantages of CNC.

> By the way, I've seen your site before, and sadly it confused me
> terribly. I'm going to try to work through it step by step tonight.
>
> (if you promise not to tell anyone, I actually got through high
> school, college, and grad school without ever taking physics...
> shh!...hehe. After all, us computer scientitst don't need any of
> that.. hehe)

Well, I wasn't great at physics, either, but it is pretty important in
analyzing these machines. fortunately, quantum mechanics doesn't
apply!

Jon