[yoobsterlol]

So I've been looking around at other people's designs for a cnc, and I have been seeing a lot of rails mounted on the side of the machine, rather than mounted on top. If that's confusing, what I mean by that is the 2 rails for an axis would have the faces of the carriages < > rather than ^ ^. Is there a reason for this? Am I missing something, and is this the best way to orient Hiwin style rails?

[ger21]

While there are some types of rails that have different load ratings dependent on orientation, generally, it doesn't really matter.
Also consider that linear rails can typically handle 10x (or more) the loads that a DIY CNC machine will subject them to.

[cyclestart]

what I mean by that is the 2 rails for an axis would have the faces of the carriages < > rather than ^ ^.

If you align the rails using the methods the manufacturer recommends having them in the same plane ^ ^ makes things simpler.
Same plane, not < >.
I think most people are letting the rails self-align and feel for binding and it seems to work fine in either orientation.
If your machine is extremely rigid the manufacturer method is the way to go.

[rodw]

The rails are much easier to align if you place them on the top surface but having said that, I mounted mine on the side as I could tuck them out of the way. I did give a fair bit of thought on how to align them vertically. IN this orientation, the torque handling is a bit less according to Hiwin but as has been said, its not significant enough to worry about.