I am designing a home CNC mill for machining nonferrous metals. I plan to use linear guides to support either a Y-axis table or the 2 legs of a Y-axis moving gantry.
Linear guides are used to provide low friction linear motion along one axis while resisting forces in other directions (both rotational and translational). They come in many sizes as shown below, and must be mounted to very flat surfaces and adjusted for parallelism with respect to a "reference" guide.
I have a number of identical linear guides at my disposal that are 12mm in width which is on the smaller end of the spectrum (although they are lower in height profile). I am curious if using more than 2 linear guides (3 or 4 all in parallel) is beneficial (provided that I mount them all in parallel). Are there any drawbacks I should think about when considering using more than 2 linear guides to guide something?
The reason I ask is (1) I don't want to waste a linear guide if this is a "weakest link" situation, and (2) using 2 linear guides is by far the most common I've seen in commercial designs for linear stages.
Someone might ask "if you're worried about rigidity why dont you go buy some bigger stronger linear rails"? I guess that's also part of my same question - could using multiple smaller linear guides additively achieve the same effect as a bigger stronger linear guide (while at the same time maybe being lower profile which I think should decrease the moment arm for the roll axis)?
Here are some diagrams from newports website if they help for reference: https://www.newport.com/t/manual-positioning-basics