Jonathan - thanks for your "useful summary" link - good to see you're still your usual patronizing little self.

Irving - thanks for correcting my shoddy maths - however you just model holding torque - most people want their steppers to move - in which case your maths say nothing.

Cret - many years ago when some folks on here were still in short pants - all I had for my first machine were unipolars and I had them wired full coil bipolar. Mariss from Gecko drive (but hell what does he know?) suggested I try half coil instead and the difference was dramatic. Try both (it's allowed) - see which best suits your requirements.