First build - Mid-scale gantry router design

[routercnc]

Welcome to the forum,

My machine has hiwin type rails on Z (15mm x 300mm) and Y (20mm x 700mm) but the X axis (900mm) is 16mm supported round rail. I can cut aluminium well and hold a good enough tolerance to press fit bearings into a bore, so it can be done with a mix like that. However, the hiwin (square / profile linear rail) are so much better and stiffer and the prices these days means that if you are starting from scratch you stand a better chance with hiwin all round.

As for 500x500 single ballscrew, my experiences are this is OK for wood, but aluminium is less than ideal as the gantry will rack a bit when you cut at the extremes. I upgraded from single to twin and it is much better. You might be OK cutting in the middle for very small parts but I personally wouldn't go there again.

Spindle to bed clearance is a personal design choice, and 150mm or so is popular, but if you go larger you will loose stiffness when cutting a full depth. Some designs use an adjustable bed, or use a purpose made 'solid packer block' to bring work up to the cutter. For me simple is best and 150mm or so is worth starting at in your design to see if it will cut everything you need.

You haven't mentioned gantries yet but an elevated X axis allows a superior gantry design(i.e. minimal / no gantry sides). Have a look at the recent build logs as most people go this way now - Jonathan, Silyavski, Eddie, Neil etc.