15MM vs. 20MM RAILS

[woodworker2]

Hi all, I am building a new cnc router with a table cutting size of 42" x 30".
I am planning on using 80/20 extrusion, and I am going to use some linear rails, either Hiwin or THK. Do any of you see a performance difference between 15mm rails and 20mm rails? just for clarification, the rail widths are 15mm and 20mm, the heights are the same on both at 15mm.

[mchabot]

What kind of rail? this is more important than size.
Four point HSR can hold load in all direction, SR not.
A bigger rail can hold higher load, wider rail can hold higher load in some direction, check manufacturer specs they are quite detailled about this.

[mactec54]

woodworker2

For long rails you want them at least 20mm/25mm wide, as the 15mm are harder to get straight in long lengths,unless you have a machined surface with a shoulder to put them on

Mounting on extrusion does not give the 15mm rail much support,3.5mm each side of the slot is not enough

[woodworker2]

Thank you, I have looked at Hiwin and THK, and I can't give you the model numbers, but I did make sure that in the descriptions, that they could be mounted in a vertical application.