Hello, Sure we can help but first, we need to know more about what you have, so give any info you have on the machine.

Do you want Mach3 to control the speed or just have Start/stop the spindle.? For mach3 to control the speed then your system must provide a control voltage which then gets passed to the VFD or speed controller board the spindle connects to.

If you just want to start/stop then it's much simpler and mach3 just controls a Relay using it's Outputs. Which you then wire your spindle power thru.

So first we need to determine if the BOB or Controller provides speed control.?