OK, that answers the question about the Sprint motor driver and if it cuts power to the motor. The reason was just to make the install simpler as I suspect the on signal from this breakout board is only 5v, as it will run from a USB cable, so would need two relays, one 5V to 24V, and 24V to 240VAC. Although it would make adding a door or chuck guard interlock easier as it can switch the 24V loop. There is also a delay switching the power supply on, and then another delay spinning up the chuck, and it may have reduced that. And not wanting to keep switching it on and off although you say it's not an issue.

Thank you for your help. It's a big hand up knowing I was on the right path.