The YOOCNC controller is mostly garbage. I've bypassed the speed control with a PWM spindle controller from ebay which works a treat. I've also replaced the parallel port interface and drivers with other ebay stuff that seem to work better and I'm no longer dropping steps. About the only thing I'm still using is the case, connectors, transformer and power supply circuit.

Quote Originally Posted by komatias View Post
The spindle motor is run off a 555 based PWM circuit with a peak of 46-50V if IIRC. No inverter just a transformer rectifier to get the DC. The machine is not very stiff so it will go through resonances at different speeds. I seem to remember mine also had a whiny spot.

2/3's of the way should be sufficient to work it. If you are really clever you could tap into the PWM trigger and get Mach3 to set the speed of the motor. Some control boxes have the connection for this on the outside, some don't. Looking up the 3040 manual on the net and opening the box up may give you all the info you need. Would have done this myself but got rid of the stepper motor board in favour of a Gekcco G540 and then lost interest in the spindle mods.