CNC Frame Design Help

[JAZZCNC]

Hello and Welcome.

Ok well for both these Tasks then this design isn't very good.? The moving bed is too weak for aluminium cutting and the level of accuracy you'll need for PCB this setup will make it very difficult and cause more trouble than it's worth.

If you need high level of Z clearence then I would look to a conventional Gantry setup but have the Gantry raise up/down in place of conventional Z axis.
This will give you high strength and great accuracy while having large Z axis clearence.
Your idea of the bed just being supported by unsupported linear guides and just one ballscrew at each side will fail badly i'm afraid. To work any where near good enough you'll need the rails supported and ball screw on each corner. Then you have the problem of keeping the ballscrews in perfect sync so the table is always perpendicular to the cutting tool.
In practice the outcome will be you'll always be chasing the bed and needing to surface the area you want to work in if accuracy is required. I build machine that use adjustable height tables and while they work great in allowing nice range of materials to be used it's not something you move up/down often because of the work involved.
Unless you build into the machine a very accurate way of keeping the table perpendicular to the cutter, Ie using Encoders or sensors etc then your design will be more trouble than it's worth believe me.! . . . . . Even then it needs a complete redesign from what it is now.!

Sorry to be so Negative but it's what I see and with the foresight of experience I see huge potential for failure or at best dissapointment.