starting from scratch- router 1st project

[JAZZCNC]

Hello Philippe,

I see several things really.

Yes change to profiled linear rails if you can afford them has they make much better and accurate machine. 15mm will be fine but 20mm often don't really cost much more and the larger bearing size helps.

Ball-screws then I'd use 1610 not 1605 if your mainly cutting soft materials has they allow higher feed rates which you'll need. They also provide enough resolution for most Aluminium work unless working to fine tolerances. If you connect to screws with timing belts/pulleys, and I suggest you do, then it's very easy to change pulleys and increase resolution and torque but at the expense of speed,
I would change the Position of the Long axis (X axis) ballnuts to mid point of gantry and have supporting braces at both sides of drop bracket not just one like you have drawn.
While the Y axis nut being high up is not the ideal it will be fine there and better there than further back but lower down.

Regards the rear plate of the moving carriage then you don't really need it has it's adds very little strength and more weight to the moving carriage reducing acceleration, also adds expense.
It makes building the carriage more difficult has the connecting surfaces and edges must be perfectly 90deg to each other else it turns into a parallelogram, any error will increase binding on the bearings and it doesn't take much to bind them solid. It also interferes with other aspects of the machine which you haven't drawn and maybe not taken into account.? Like cable management. The rear of the gantry is perfect place for Cable chain and with the plate nothing can be fasten at the rear.!! . . Simple thing but can be annoying.
Not having it takes nothing away from machine and makes building easier and less work. Just machine the top bearing plate so the ballnut mounts direct to this and is central, the bearing plate will extend back above the ballnut then you can bolt down direct into the ballnut mount from above so doing away with the drop plate and potential weak spot.

Regards the Gantry then I'd consider having some Triangle gussets around the back strengthening the connection between sides and gantry cross piece, these braces are simple things which really help with resonance dampening.

One last thing.? The Z axis rear plate doesn't look very tall so you may find you need to extend this from how you have it drawn now.? How do you plan to build Z axis.?
With the short back plate I'm getting a feeling your thinking to have the motor travel with the front plate but I'd recommend you don't has it's harder on the motor and reduces acceleration. It makes using Belts to connect motors to screws harder and I suggest you do use timing belts/pulleys has it's better for few reasons. Mainly smoother working motors due to better resonance handling and flexibility regards fine tuning if needed.

Oh and think about capping ends and using Dry sand rather than Concrete has it can be removed for when moving and dampens vibrations very well.