Hi, I am in the middle of gathering parts for my home made fixed gantry cnc mill.

At the momment, I have 2 pcs of 25" 20mm rails with 2 slider blocks on each rails. I plan to use this for the table axis (X axis). I still need to find 4 more rails for Y & Z axis. I have the Y axis length in mind at 18". The question is, what is the ideal length should I choose for the Z axis? 12"? 10"? or 8"?

Also, If I use a long slider blocks (92.4mm long with ratings of 1900kgF Dynamic (C) and 3330kgF (Static (C0)), how many sloder blocks should I use on each rails for the Y axis? I will use 2 rails for the Y axis too.The rails width is 20mm.

Thanks in advance.

Dexter