Limit Switch Ground

[kolias]

My home made CNC router is working well since last June and have done a lot of hobby work but I had ONLY 3 instances where the Z axis plunged uncontrolled 1” thru my stock and into the table in a matter of a split of a second before I had a chance to hit the Estop.

The gcode each time was asking for only 1/8” depth. I have traced a possible problem to a loose connection in the XLR connector which I fixed but to provide an added safety I grounded the 3 motor cables and also installed a limit switch on the Z axis.

However I had some problems with that limit switch. First by wiring the COM + NC connections to my BOB I was always getting on mach3 the message “Limit Switch Triggered” even when I was switching the polarity (active state).

Then decided to wire COM + NO connections to my BOB and then I got it working nicely. Strange isn’t it? But having a limit switch wired like that is not safe.

Then thru another forum I was told to re connect the limit switch as COM + NC and set the parameter “Debounce Interval” on mach3 to 2000. That worked nicely. Apparently the “Debounce Interval” parameter filters noise from the cable and then I was told then to ground the cable from the limit switch.

I connected the ground from this cable to my DC ground bar in the same screw as I have the ground from my 3 motors but now I was getting the same message “Limit Switch Triggered” even when I was setting the “Debounce Parameter” from 0 to 2500. Somehow by grounding the cable I was getting much more noise.

Now I operate my CNC without grounding the limit switch cable and with the parameter set at 2000.

Any ideas why I get more noise when I ground the cable?

Nicolas

[kolias]

I'm surprised no one provided an answer but I got help from another forum.

All I did was to install a 0.01uF capacitor at the control end of the limit switch wiring and now the "noise" is completely gone and the "Debounce Interval" is set back to 0.

Very simple and effective. Perhaps other forum members can find this info useful.

Nicolas

[Scramjet]

Hi
Think is little late you found solution, but thats right, i did same with my encoders cables and noise gone, think is same for switches, maybe is becouse the power of the bob needs to be higher i mean in terms of current, maybe is too low and needs to be filtered by capacitors.

E. Chan