This Friday I will be prototyping the spindle control. It will be a PWM configuration using a 555 Timer and IRF510 Mosfet. The schematic I found uses a diode to protect the circuit from the motor but it doesn’t say what kind of diode. It lists a 1n4148 diodes for other parts of the schematic but I doubt it will work well for this so I might use a 1n4001.
I rather control the spindle speed by hand then having the main controller doing it. I plan to use 5volts to power the PWM circuit and 12volts to power the spindle itself.