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.

enter image description here

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.

enter image description here

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)?

enter image description here

Here are some diagrams from newports website if they help for reference: https://www.newport.com/t/manual-positioning-basics

straightness deviation: enter image description here

tilt rigidity: enter image description here

load capacity: enter image description here


1 Answer 1


The idea is mostly sound.

I have a load F that is too high for my linear rails....so instead of beefing up my rails, I increase the load sharing across 3 or more rails, thus dividing it.

In reality, I have actually seen such things....but only on poorly built machines as a half solution.

In general one can do anything they want....but that doesn't mean it's the correct way to do it.

Linear rails are specifically designed for uses of 2 rails for a specific type of load and/or torque, in various orientations and environments within specific tolerances and drift or alignment tolerances.

Beyond this, trying to align 3, or four rails along a linear axis accurately, without them binding or causing premature wear on the rails or carriages themselves would be tedious and difficult.

But it is possible...you just wouldn't see anyone do it.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.