How much torque is needed?

[Cold Fusion]

I'm looking into buying a Bridgeport Series 2 nc mill and retrofitting it with a pc control. Since I'm comfortable with the gecko system, this is what I want to stay with. Now the question becomes stepper or servo, as well as how much torque. I'de like it to be a decently fast system, but rapids over 100ipm are not needed. I forsee a lot of aluminum being milled, and on rare occasions steel.

[ESjaavik]

Here is the "works for me" figures:

My mill is about the same size. I run 10Nm stepper on X, 6Nm on Y, and 12Nm on the knee. The last one is not strong enough, I can only run around 50mm feedrate in Z. X and Y will do F=600mm. This is with preloaded ballscrews 30mmx5mm on X, 23mmx5mm on Y and 32mmx10mm on Z. For Acme screws you need 2-3 times bigger motors.
The drives runs 12A/70V on X and Z, and 9A/70V on Y.
X runs directly on the ballscrew, Y over a belt, don't remember but it's close to 1:1.
Z is geared down quite a bit, I don't remember how much at the moment. Anyway it's my recommendation you try to move the quill for a much faster Z. I have just not found out how I can do that with enough accuracy on mine. On the BP there are several solutions.

I might add that on my machine Y moves the spindle and not the table, so it has a lower mass than X (the table).

I'm not satisfied with the speed, so will upgrade to servo. It is my prediction you will not be satisfied with 254mm/min after a short while.

[Cold Fusion]

I've been researching servos and it has me very confused. Do I want DC, AC, brushed, brushless? The stall/continuous ratings also has me a little confused.