Moving off steppers and on to the spindle motor:

I spent this afternoon setting up the inverter and its control in Mach. I found that by fiddling with the PWM base frequency that I could get 100% on Mach spindle control to correspond to 100hz on the inverter (which previously it would not).

Having sorted this out I turned to pulleys and defined the four motor speeds as pulleys. I then calibrated the spindle speed to a range that I thought would work without me having to move the mechanical variator (Reeves type drive) or even replace it with a single fixed ratio poly-v-belt drive. I reasoned I needed speeds between 150rpm and 4000rpm. However, having run the slowest speed of the motor at the lowest reasonable frequency I quickly concluded that the motor has insufficient torque at this speed.

So I've decided to use be able to use the variator in two positions giving tops speeds of 2000rpm and 4000rpm with plenty of low-down torque in the lower range setting. I'll be mostly machining cast iron and steel so the lower range will be deployed most of the time.

As I understand it Mach3 while it's possible to tell Mach3 the spindle speed it cannot change the pulley setting automatically. It would have been nice if one of the four motor speed control relays could have been linked and operated by this feature of the software, but I guess I'm hoping for too much! In any case I'll have to set the variator manually.