Quote Originally Posted by gamingan View Post
I really prefer the rails mounted on the sides because it also does a bit of dust shielding.
Dust is going to be an issue, regardless how you install the rails. A word of advice is that you already at this stage think about dust extraction. Not only the linear rails which needs to be protected from dust but also the room where you are planning the use of this machine. So personally, I'd mount those rails on the top, as said by others, but I'd also design a dust extractor, a simple dust shoe, as well as some side walls, which not only provides some protection for the rails, but also personal safety.