I am about to begin building a very large CNC router for creating timber components and have had quite a bit of difficulty finding information on this forum, or anywhere on the internet, about building very large scale cnc machines. Lots of the machines I see being built are quite a few steps smaller than the machine I need so I am having quite a bit of difficulty deciding on the the details and design.

I will be using the machine to create joinery in large solid wood timbers (8x8, 6x12, 6x6 etc), I use everything from white oak to pine so the machine must be able to handle the hardest of woods. I will mainly be using a 7 inch long, 3/4 inch diameter carbide cutter head. My goal is to be able to use this cutter head to create 1/2'' - 3/4'' depth of cut which will allow for very aggressive material removal.

I see lots of build threads on here where the original post has lots of the design and details figured out, or at least a strong direction for the machine, I unfortunately cannot decide which way is best to approach this build.

I am posting in hopes the talented people of this forum can guide my decision making, so here is where I am at now:

-Spindle HP: 10 minimum (I have been in contact with a forum member who has a used 12 HP komo spindle which seems to be a good for for this machine)
-Work envelope: 48'' X , 120'' Y, 16'' Z
-Gantry style design
-I am really hoping to use large stepper motors instead of servo's, accuracy is not extremely critical in this application
-I am thinking rack and pinion to create movement
-square linear motion rails
-Welded steel frame
-Rapid feed rates and very quick movements are not critical, the depth of cut is much more important. I have seen that a lot of builds decide what the rapids and feed rates should be and work from there, but on this build the aggressive depth of cut will be the starting point for feed rates. With this being said, it will be a machine used for my business, and time is money, so an efficient machine is critical.
-Mach 3 controller


So with this being said, I cannot decide on a starting point. I am torn between the following:

-A gantry with high vertical uprights (I think this is referred to as low rail design)
-A gantry that sits on high frame rails (I think this is high rail design)
-A moving table (Table moves only in Y direction, Gantry moves in only X direction)
-Some other approach I am not even aware of


I am hoping the talented people of this forum can chime in and aid my design process!

Thanks,
George