Hi again,

Your thinking is wrong here.? It won't be low cost learning at all because the biggest investment in a cnc machine is time and this will take the same if not more time than building something that's properly upto to the job made from steel. Then there's the wasted cost of materials, Wood, glue, screws, nut's & bolts etc all 100% unusable on a real CNC machine.
One 7.5mtr length of 60 x 60 x 4 steel is about the same money as one sheet of top grade ply which you would need to use to have any chance of half decent wood based machine.
Now two lengths of steel will easily build you a machine around the size or possibly larger than that machine Dave is building but it will be much much stronger and take a fraction of the time to weld up the frame than cutting and shapeing plywood.
Welding isn't difficult and you don't need Xray quality welds, simple cheap MMA stick welder is all that's needed and bit of practice on some scrap. if you have access to a MIG welder better still any chimp can weld new clean boxsection with a MIG.

Then we have Electrics ~ There is no cutting corners here if you want a good CNC machine. Electronics are the heart of the machine and cheap electrics are like starting life with heart condition, you can't run fast or breath properly and sooner or later your going to need either a transplant or have coronary.!!

My point being in all this is it doesn't cost more to do it correctly it's actually much cheaper in the long. Yes the initial outlay is more but your only doing it one time and not throwing it all away to build a propoer machine. Trust me on this TIME is where the true cost lies in building a CNC machine Good or Bad there's a lot of time invested so what's the point investing time in something that you know you'll only have to do again.??