Re: [CAD_CAM_EDM_DRO] Re: Servo controllers for table top machines.

William Carr wrote:

>I recall I was doing a 1/2 inch deep 2" x 2" cutout in foam for
>practice and was puzzled to see it started 1/2 inch deep and ended
>1/4 inch deep at the end.
>
>
>I was told to turn down the z speed. But that converting to servo
>motors would also solve the problem.
>
>So I second the question, why do companies say that servos are
>better? Marketing?
>
>
>

Your machine made a positioning error, and only your EYES caught the
problem.
The computer and machine went on blindly working the part -- WRONG! Because
this was insufficient Z depth, the parts might have been able to be
remachined,
but if it was X or Y, or the Z erred the OTHER way, the part would have been
scrap. I guess it didn't matter as this was a foam test part, but it
could have
happened to an expensive casting or something, and you'd really be mad!

With real servos, any positioning error will be caught. Depending on
the way
the servos are set up, you can have very tight bounds on the allowed
positioning
error, and exceeding those bounds stops the machine. It can't guarantee
that
the part can be saved in all cases, but it certainly guarantees that
only one
scrap part would be made.

Excessive speed and/or acceleration is not the only cause of lost steps (or
servo stalls), it can also be chips in the ways, failure of the lube system,
running the tool into clamps and vises, part slipping out of vise, failed
cutting tool, etc. You want to know if any of these situations develop.

Jon