I'm very fond of my pin 1 strobe safety, which locks out all power to the contactors unless it can see 12.5KHz on its pin - And since mach3 starts in Estop mode, it hasn't clunked once since i wired the thing in. I could hear a few clunks and grumblings from the relays and contactors before i fitted the strobe safety, it's dead quiet during startup now. I'm also putting in an interlocked safety for tool changing so that not even an M3/M4 command will start the spindle while a tool's being changed. Worth doing since i won't be the main user of this machine... other people's fingers are VERY expensive.