Quote Originally Posted by danilius View Post
Loads of luvverly advice, thanks!

Is the direct drive on the z axis such an issue? Should I make that belt drive as well?

Is there a disadvantage of using two Y motors? Sure, they can get out of sync, but surely two homing switches/sensors should take care of that between jobs?

I was not sure about that. My thinking was that by using two Y motors, I could save some weight, and the two motors and lead screws would compensate for the added stiffness the connecting plate would provide. Is this incorrect?
belt transmission gives you extra flexibility, you can adjust gear ratio means=feed, easier do deal with resonance if any occurs, allows to mount motor in two position (up side down and shaft up).
Z axis takes most vibration as is driving spindle up and down, so those shaky shaky gets to the motor and disturb in high speed. My first machine was driven by coupling - cheap Chinese, than with plastic insert, odiham finally end up with 1:1 pulley.

Y drive, if your power supply can handle biggest nema 23 3Nm motor without extra voltage than one motor should be ok and will wait only few hundreds grams more than 1.9Nm. Advantage of having one motor and two ballscrew is lack of need for squaring the gantry (one motor less, 2 sensor less)
Motor have to be powerful enough so they do not loos steps, if you loose steps you loose your job, material, time.

Gantry - more braces make it stiffer - joining them under bed will increase the weight but benefit you gaining by stiffer, more accurate machine are far more important.
I hope somebody else will give you some inside, I only build 3 machines and even on last one I would make something different, now I designed another one will post it soon.

Good luck with the build