Re: CNC machines from plywood
It is quite possible to build a good plywood CNC.
Unfortunately your design has many weaknesses.
It seems the people inevitably start - designing a CNC that looks like they think a CNC router should look like. Many of the early DIY CNC router designs are very poor but are still around and influencing current designs.
I recommend you do some reading on stiffness and the engineering principles behind a stiff machine.
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)