Hi All,
I too was having major issues with the same setup until I rewired my spindle with shielded cable. I also earthed everything back to a single star point and now I could not be happier. I was getting false stops and Mach3 would hang as soon as the spindle started. I shielded both ends of the spindle cable and added an earth to the spindle, PC and controller box in a star configuration. I also cut some small ferrite cores of an old VGA cable and added one to each end of the RS 485 cable. Please also ensure that you also use a shielded twisted 2 core cable for the RS 485. I also added an EMI filter on the input of the VFD which connects in series between the 240v outlet (Aus) and the mains plug on the VFD. I completed all of this at the one time, so I can't be sure which part was the most effective but it is now a totally stable and usable machine. Please also don't forget to uncheck the 'Disable Spindle Relay' checkbox if you haven't done so already as it will prevent some of the spindle M commands from operating.
Regards,
Damon