Fingers crossed it'll cut ally

[Tenson]

Mark, I've just skim read this thread in one turn, so forgive me if I missed the details. Have you got the PSU sorted for the big motor?

I also built a spindle with a large 270KV motor. I then modified a 750watt PC PSU to have a variable output voltage on what was originally the 12V line. Although I can make the PSU output any voltage unloaded, when the motor loads the PSU the voltage drops down the the point at which it can supply that amount of power*. I found that even driving the motor with 750watts didn't give a significant amount of cutting power; I can take 0.5mm cuts with a 6mm tool at 80mm/min but it is not very clean and the spindle RPM is too slow for 3mm cutters.

*The PSU will always limit at 750watts (this is a natural limit, not a protection circuit). Since the load of the motor is fixed (0.36 ohms), and the total power is fixed, the voltage must drop to 16.5V. I decided I need more power, but I'm not sure how to get it; even a budget ATX PSU >1000watts is not cheap.

[blackburn mark]

Mark, I've just skim read this thread in one turn,

owch! that must have taken a bit of doing.... well done.

750watt

that should be loads! something not right there... i used a 300w pc supply for quite a while (managed to trip the supply out a couple of times while using a hole saw... besides that its managed ok?)

im now on a cheap 12v 350w china special iv not tripped that one so far

im assuming your saying its to slow for 3mm tooling in wood ?
90% of my cutting is 3mm single flute in acetal between 1mm and 3mm DOC aprox 2000rpm between 200 and 300 feed

at 270kv you would need 48v to get aprox 13000rpm ... might be a tad fast if your using double row A/C bearings unless you have them swishing around in a nice light oil ?
you might have problems with the esc and windings getting hot

id be tempted to make a second spindle with a higher kv rating .... 890kv would give you 10680rpm at 12v