Concern one;

A friend asked me how this project will meet the "connectivity" requirement of the Hackaday Prize. I'm not sure I liked the phrasing; it sounded like they were suggesting I was just going to cobble something on at the last minute.

I don't think anything needs cobbling on. What will be used for debugging and control in the prototype will become a data-logging output. Tying control into existing CNC control methods hardly seems pointing out.

Data-logging isn't anything fancy, but it's extremely useful. Being able to plot current use and RPM for certain cutting speeds and tools could help you find the optimum feedrates you can handle, or watch for worn tools. Or you could simply keep an eye on how much power you're using, or even just general machine health (free-spinning current is higher than it was last month for the same speed? That doesn't sound good).

That's all just software though, this just gives an all-in-one way of accessing it. With a simple serial output, I expect there'll be many more ways found of using it all than I can imagine alone.

Obviously I'll have the microcontroler opto-isolated from any high voltage stuff. USB ports are better not on fire.

Concern two;

Is it really nessesary to have the special power supply? Couldn't I make do with just using better fuses as a safety?

Maybe.

It may be overkill to have it arranged this way. And if you want to do it "treadmill style", you should be able to just replace the whole PFC power board with a rectifier and set the apropriate range limits in software (Id: that's a good idea actually, I'll put it in as a redundant config option).

Personally though I don't like it. Just doing PWM off straight rectified mains is going to be electrically noisy for one. I also have a suspicion that even though a limited PWM duty keeps motor speed down, the high-voltage peaks that still go through the motor are what causes the most common failure; overheating.

If using a properly regulated power supply from the start solves the issue of motor-overheating, I may be able to remove the temperature interlock from the design completely. But this is again entering into the "black magic" area of motor control, so we'll just see if behaves well enough when the time comes.