On the smallest mill I use regularly It has developed the habit of going into E-Stop when the coolant pump starts and stops. Its controlled by an HH52P 24VDC coil relay. The same model relay is used to control the spindle on-off signal to the VFD.
All I use this machine for is engraving, but its still annoying. I have a simple work around. Start the coolant pump manually (on screen button), and if it trips the e-stop reset and start it again. Then begin code execution. To be honest its not that big of a deal. The shop is busy and I mostly just want to get parts out the door. Still I think it has to be a simple noise problem of some kind. Maybe an especially noisy arc when the relay actuates.
I'm going to try a new relay. These are probably the cheapest Chinese relays available. (I did have to replace the spindle start relay a couple years ago).
What do you think is most likely? Do you think there is a way to mitigate it? Maybe with a choke? Possibly a diode on the coil trigger input?
I think if it is the relay itself its most likely the primary contacts because it happens sometimes on both pump start and pump stop. Neither affects the machine position since both happen when the machine is momentarily stationary. Its just annoying.
It did not happen at all for the first several years I owned it, and it is the oldest CNC machine I use regularly. (almost everyday)
It is a Mach3 controlled machine using a Smoothstepper for the motion interface between the PC and the BOB. The wiring is pretty clean and orderly and I have checked every connection on the machine.
Other than being a cheap (relatively) Chinese cast iron dovetail mill, that like many I had to fix before it was passable to use, It really doesn't have any other problems. Before getting other newer machines I made a lot of molds with this little machine.
Well, now to order some more relays.