On 11/27/2010 09:15 AM, Pete Keillor wrote:
On Sat, 27 Nov 2010 08:29:07 -0600, Ignoramus18541
wrote:

snip
Controlling the spindle is slightly more important, as it lets me
change tools. But, I suppose, I could turn off the spindle manually.

Personally, I would be leery of changing a tool manually under a
program stop. I'd much prefer to turn it off manually. I wouldn't
want my hands on the spindle without being certain it wasn't going to
move. Or are you using a tool changer?

Mind you, that's in theory. I have no cnc equipment.
Well, I have no safety override, so the spindle is under computer
control all the time. However, the PPMC hardware does have a fairly
comprehensive E-stop circuit with a watchdog timer, so if it loses
communication with the computer, it goes to E-stop and shuts off spindle
and servo drives.

I have never had an unexpected spindle start or other wild event.
Just connecting a VFD to the parallel port, without some kind of estop
and watchdog circuit sounds risky, though.

I'm pretty sure I've seen Stuart Stevenson at MPM change tools without
e-stopping the machine, and those machines would throw you across the
room if the spindle started when you weren't expecting it.

Jon