Was about to get a toy- then I did some research...

[Juranovich]

Those motors sound a little weak to me. You should use the motor calculation sheet to determine what you need. Mines a similar size, and I use 2x2010 X screws (2x4nm low-inductance nema23 steppers) and a 1610 Y screw (3.1nm).

I'm at that stage where I think I've figured out the basic mechanics of a CNC, but I now start to realize all the intricacies of the fine details. So thanks for pointing me in the right direction. I suspect I'll go for 1610 on X and Y to avoid whip and keep the 1605 on Z for precision. As I decide on the final gantry design (and the associated weight) I'll get back to the motor calc to figure out the steppers needed. Just one question though, if I have two steppers driving the long axis, should I input half the total weight of the gantry in the calculator?

Also, you don't happen to have any comments on the frame?