Re: Limit switch problems..observations

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@y...>
wrote:

> Hello,
>
> Caudlet, I agree with nearly everything you wrote...
>
> But some additional physics might be worth observing. A spinning
> cutter, engaged in material, is an accident waiting to happen if
> cutting the power allows it to backfeed, even while it spins down...
>
> A broken cutter is likely, and like so many accidents, the

secondary

> result can be worse than the "caused it" problem...
>
> Killing power is not always the best estop. Be sure to COMPLETELY
> think through the results of an estop, given the SPECIFIC machine
> setup.
>
> Hope this helps,
>
> Ballendo
>
> P.S. What's safe for steppers is not the same as what is safe for
> servos, and vice versa.
>
> You may be right but I have to make the assumption that if you hit

aa limit, or hit the big red button the cutter is already chewing up
soemting it should not (if it is in the material). I realize there
are issues with big mills that could present some nasty sceneros, but
if the machine has gone off in the weeds and is cutting fixtures,
worksurfaces or itself then short of dynamic braking I can't think of
a situation where I would want it to keep moving. I realize that
removing the power from a motor will leave you in a free wheel
condition and a big ole cutter spinning could hang in material and
move the table but I trust the software even less (and I am an IT guy
and programmer) to stop things. I do have low ohm power resistors
that short across the motors and present a level of braking. At the
hobby level the tendency is to just wire it and go...often with no
limits or e-stop at all. Most of us are not running 10HP mega-
mills. My servos drive ballscrews and a pretty heavy gantry. When I
remove power they stop even when I had a 3HP router cutting oak.

Like you say, you have to weigh each situation and design for worst
case.