I agree that your first machine will probably get scrapped. So the threaded rod will be just fine.
When you build the final one though, I wouldn't consider anything other than ballscrews. Note that with a good ballscrew, say 3/4" diameter x .200 pitch, placing the screw in a vertical position, the nut will spin from top to bottom with gravity alone. This lack is friction is exactly what you want.
Likewise, good linear rails that don't bind will make it such that the load on the motor is almost purely inertial, with very little frictional force.
You'd be surprised at how a tiny 270 oz-in NEMA 23 stepper motor powered with a 24v power supply and less than 2A of current is perfectly capable of moving a 100lb gantry at 150IPM, assuming ballscrews, quality linear rails, and 1.5 to 1 gear ratio.
Compare this to a mill table. A 9x42 weighs about 150-175 lbs, but would require at least a 640-oz in stepper with a 48v+ power source and 3 to 1 gearing to move it at 75-100 IPM.
Friction sucks. |