False Limit Triggers - Cutter Dependent???

Hi,

I've got a quarter-sheet CNC Router that was built from a kit. It uses stepper motors via a G540 via a parallel cable to a PC with Mach3. The spindle is a water cooled chinese unit controlled via a small VFD that is also connected through the G540 so Mach3 can control the spindle.

Since I first set the thing up I've had intermittent issues with false triggering of limits. I've played with the debounce interval in Mach3 and a few other software settings and for the most part it's calmed down to where I'm not overly bothered, but yesterday I was cutting with a 1/4" bit I don't usually use and it was triggering all over the place, generally driving me nuts. I'm hoping by posting some of the symptoms I can get a little insight on what to do to debug this. Here are some facts:

1. It only triggers when the bit is actually cutting. If I restart the file from the beginning, it will air cut until it gets to where it died before without triggering. Ever. Once it's cutting again, sometimes it will go for a while and sometimes it will trigger again almost instantly. But it never triggers if the bit isn't cutting. To clarify, I'm cutting wood, so it's unlikely this has something to do with grounding the bit to the work.

2. Seems to be somewhat bit dependent. As I said, I don't often use this bit but after one of the (many) shutdowns I screwed up and jogged the machine with the bit down and sheared the bit off. I didn't have another of the same bit so I put in a 1/4" bit of a different type and saw FAR fewer (though not zero) false triggers.

Taken together, I'm betting this has something to do with noise from the spindle, exacerbated by vibrations from the cutting process, but while that seems a reasonable thought based on the symptoms it also strikes me as incredibly odd. Regardless, I'm not sure if that's really the problem and how to fix it if it is. I'd love suggestions.

Thanks!
-Ben

Are you using shielded cables all around. Both for your steppers and for your spindle???

And are they grounded correctly?

Quote:

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Originally Posted by benha

I'm betting this has something to do with noise from the spindle, exacerbated by vibrations from the cutting process, but while that seems a reasonable thought based on the symptoms it also strikes me as incredibly odd. Regardless, I'm not sure if that's really the problem and how to fix it if it is. I'd love suggestions.

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Your prob right Ben. noise is the culprit 99% of the time on low cost mach3 from pc par port output setups. Realize that the more CURRENT (load) your spindle pulls (aka, cutting) the higher the noise.

cutting vibration has NOTHING to do with it.

so. you gotta work on shielding and grounding. lots of past posts on it. basic 1rst todo items:

1) ground pc chassis
2) ground spindle motor body
3) be sure all ur LS use shielded cables.
4) use 4 conductor shielded spindle motor power leads
5) do set those mach3 debounce settings higher.
6) run all POWER wires SEPARATE from control wires
7) tie ALL shields at BOTH ends to ground
8) have ONE common ground strip for everything and take it back to your best local ground with one wire