Quote Originally Posted by Jonathan View Post
Since the system is symmetrical, we can model it as a single ballscrew with the length doubled and twice the pulley inertia. The calculated torque is 0.75Nm (or 1.09Nm with 30T pulleys). That's still within the ratings of the 3Nm motor... so no need for a Nema 34 motor (though it would clearly work, just be more expensive). If you want higher resolution, you could use 16:20 ratio (16T on motor) and the torque required is 0.55Nm.
No sorry lovely calculations and all that but I can tell you from experience that 1 x 3Nm Nema 23 motor connected to 2 x screws with timing belts won't handle what will become 60Kg+ gantry and be reliable.!
Yes it will move it no problem and work but when the cutting gets hard or the speed and direction changes are fast it will struggle and the chances of lost steps makes it unreliable IME.
Either twin 23's or Single 34 is the way to go for this size/length and weight IMO.