My first go at making a CNC router

[Norgmonster]

Hi All,

I've been working all week so no time to post much.

I'm learning Fusion and getting my design nicely visualized. In doing so i have come up with some questions:

For my X, Y and Z axis I'm thinking to use Hiwin rails and blocks. What size blocks would be sufficient / not overkill for a R&P driven, 4x8 bed? I'm thinking 20 but would 25 be better? Also, as the axis gets smaller can the rails get smaller as well? For example, 25 rails on the x, 20 on the y and 15 on the z.

Also, is it worth using a belt between the stepper motor and ball screw on the z axis to prevent backlash. If the stepper motor is directly driving the ball screw then will an anti backlash nut be sufficient seeing that the travel is only around 20 - 30cm?