Im working on determining the best method to make a gantry type PCB router (machine max size would be 24" x 24", probably smaller).

I think using linear rod bearings and a ground shaft system will be what I go with, but some of the finer details Im not sure about. Using the rail system under the table edge will help keep dust off it, but I have different options, and I am not sure which would be the best for accuracy.

Method 1 - Have a rail down each side (will be the y axis) and have a center feed screw

Method 2 - have a rail down each side and a screw feed down each side (using a 4 axis controller system)

Method 3 - same as 2, but use two rods down each side with the feed screw between

I am hoping that I can get away with 1 rod per side and use 2 linear bearings spaced apart for extra rigidity, but this is only a guess. I also dont know if one rod per side when using 2 feed screw will cause a problem (should the feed screw be above the rail or below, and will it cause the gantry to angle slightly when moving ?

I guess my big problem here is I want to pick a method thats the cheapest and easiest, but not if it messes up accuracy, which im sure I need with PCB milling. Being stuck here really prevents me from proceeding on parts gathering and build start. Im sure that the people here can help, as you have already sent me light years ahead in CNC knowledge in a very short time.