[cadmonkey]

Yes you could top mount the Z and keep the handwheels. Be forewarned - mentioning keeping the handwheels on converted machines can start a flame war around here... I'll just say this - keep in mind the wheel is at just the right height to knock you in the *^$s when you're running under automatic control... You can do manual work with the CNC software either by jogging or entering in G code on the fly. You can have the quill extended and locked a bit and still be rigid enough, just not too far, especially with larger cutters. If you want to send pulses back with steppers you need to add encoders onto the shaft and read those - just like servos do (though some servo drives don't route the encoders back to PC, they just throw a fault when they haven't seen the complementary amount of movement as has been commanded). I don't know what results 1/2 stepping would yield on the ACME screws as far as resonance and resolution go. Sorry.