Motor type and sizing help

[AcuBill]

Hi

I am in the intitial stages of designing a CNC table that would drill holes and also be able to switch out out and put a plasma cutter head on. I am planning on a 4'X 8' table with the gantry moving X & Y with about 3-4" Z movement. I am planning on using a rack and pinion and would like to direct couple the motor to the pinion shafts. (but may change if required) Same possibly for the other motion.

I have no idea how to size or what I should look for in these type motors. Main thing I am looking for is something cheap. I am not familiar much at all wether to use a servo or a steppper. Waht the differences between the two would be or cost. I can supply any ther info to the best of my knowlege to get a better answer.

Thanks much

[Al_The_Man]

Motor sizing depends on many factors including required max. rapid travel/feed rate, weight of gantry etc, if you intend doing drilling you have to have a solid method to counter-act the forces on the Z axis due to this operation.
Also, it is very rare to do a direct drive from motor to pinion, especially on the size of table you are looking at, due partly to the inertia factor when requiring fast acceleration. Typically with direct drive you would be moving 4 to 5 inches/rev of the motor.
Al.