Lead Screw Pitch recommendations?

I am building a 1.8x1.5m CNC. Mainly for plywood and possibly small aluminum parts if that will work.

I will use Nema 23 motors and trapezoidal (metric) screws.

So what pitch should I get? 2mm? 12mm? (pitch=linear travel per revolution)

12mm

Why? According to this it would require about 0.8Nm. More than the motors supply. The 222N are 50lbs which I found as a reference for routers.

Attachment 238542

Ah wait. 0.8Nm from the lead screw vs 3Nm from the motor

I think what is generally accepted is that hobby machines flex a lot. Considering this, it is a waste to have a low pitch, because any extra resolution because of the finer pitch is not realized because of the machine flex.
So what makes sense is to pick your pitch to get higher speeds, so you dont fall asleep watching your machine travel from end to end.
with steppers 2mm pitch = 0.01mm per step and maybe 2000mm / minute max speed.
12mm pitch = 0.06 mm pet step and maybe 12000 mm / minute max speed.

So I would recommend the 12mm pitch also. unless you think your machine will flex less than 0.06mm then you can lower the pitch, to exchange resolution for max speed.

12mm pitch gives you a good mix of resolution and speed. It's pretty much the generally accepted standard for a good performing, low cost router.

Keep in mind that there are hundreds of different Nema 23 motors. Some will work well with those screws, and some will not.

Thanks. Ill get 8mm pitch then, since this is the only one readily available for me.