Best location to mount Racks on a 3m Long Axis?

[joprinz]

I'm designing a 3m x 2m CNC Router. Considering the length of the axis, most advices I get are to go for a Rack n Pinion drive for X and Y Axis. I am using Linear Guide rails (20mm) with 4 Carriages per Axis. I have also found 1.5 Moduli Racks n matching 1.5 Moduli 20 tooth Pinions.

However I have the following doubts:

1: What will be the Best location to mount the Racks? I intend to go with One Rack per Axis. But I hear mounting on one side of the axis could cause racking. Is it a common problem even if we are using Linear Guideways? if so How bad will it be?

2: I could redesign the table in such a way that I could mount the Rack in the middle of the table underneath the table top (similar to what we do for Ball Screws). Is this a good Option?

2: Do All commercial long axis CNC Routers use two Racks per Axis?

Please Advice!

Joe