Bert, thank you for your comment.
180N/0,05mm may be wishfull thinking. I can probably reduce that requirement to half, with 8mm 1fl carbide endmill doc=20mm woc=0.5mm S24k F7238 P=0.82kW CF=8.5kg, but even if that proves to be unrealistic, it cannot get worse than my current setup which can complete the part.

I've made my own calculator (gulp) using example calculations I found in THK/NSK catalogues. It calculates inertias, drive and acceleration torque, required pulse frequency, resolution and max feed using following params:
- screw lead, diameter, length, efficiency
- sliding mass and friction
- cutting forces
- acceleration and direction (vertical or horizontal)
- gearing (number of teeth, gears inertia)
- dynamic friction torque for preloaded ballscrews and support bearings (basic torque based on BCD and preload for ballscrews)
- rotor inertia
It shows warning if max feed rate is compromised by ballscrew critical speed or there's an inertia missmatch greater than 1:3

I've just checked it against the calculator I found here:
http://www.mycncuk.com/threads/1524-...otor-do-I-need
basic calculations seem close (it has acceleration locked to max feed), and it seems to suggest motor with 3x the required torque.

With steppers I would need 10mm lead ballscrews rotating @800rpm. X axis max feed (rapid) would be compromised, and that could be handled with 20mm lead ballscrew and stronger motor.
With 3000rpm ac servos, Y and Z would need 2.5mm lead direct driven ballscrew or 5mm lead geared down up to 1:2. X would have to be 20mm dia 10mm lead ballscrew geared down to 1:2.5 to keep it spining under the critical speed.

I'd like to reduce the footprint of the machine as much as possible, so I would hide motors inside a column and use belt driven ballscrews, otherwise, direct driven ballscrews would be better solution in the long run since I wouldn't have to worry about belt wear (I'm using belts on my current setup).

If pulleys are used, I would like to use shaft-to-pulley clamping devices (sleeve coupler?), but they would increase the required number of teeth (diameter) of motor side pulley raising the motor side inertia significantly.

X axis 2010-1300mm ballscrew could be driven by 400W AC servo (1.3Nm, 360gcm^2, 3000rpm, 2x2500p/r) geared 24:60 providing 12m/min feed rate @ 250kHz, 0.8um per step resolution.

Inertia wise, for Y and Z, 16mm dia ballscrews would be ideal, but with gearing it seems that 20mm would work and it would be stiffer. I'm considering new ballscrews I found on ebay (could be cut and remachined, but calc for actual length)

Y 2005-284mm balscrew driven by 200W AC servo (0.67Nm, 134gcm^2, 3000rpm,16bit enc) geared down 20:36 (motor side sleeve coupler cannot be used since pulley dia is too small) providing 8m/min @ 330kHz, 0.042um/step resolution

Z axis ballscrew would not have BF support, reducing it's length to 160mm (w/ double nut). It could be direct driven with 200W AC servo, but if I want to hide the motor inside the column (and thus introduce pulleys), I have inertia problem. Again, if not using sleeve coupler for the motor side pulley, I could go up to 20:36, but with coupler there is no solution for 135gcm^2 rotor inertia (14mm motor shaft requires coupler with 26mm outer diameter, and I guess that minimum pulley dia is at least 10mm larger - 24T pulley, and that pulley introduces too much inertia on the motor side). So, solution is either with 20T motor pulley with set screws or direct drive and motor sticking out of column.

With 16mm dia (or less) ballscrews, total inertia drops, shaft end has smaller diameter so smaller sleeve coupler could be used (not very significant since it's on ballscrew side). It turns out that Y and Z axes could be driven with geared down 100W motors (smaller shaft dia - smaller sleeve coupler, less teeth on pulley), making 12mm ballscrews ideal in that respect. And there's my question from previous post :)