Linear rail weight bearing capacity

Hi,

I am trying to calculate the minimum linear rail sizes that can carry my Y axis and Z axis cars. .The Z axis carries the X axis, so it has two 8 mm rods, a Wade's extruder, a Nema 17 stepper, a plastic X car with four 8 mm bearings, 3 fans and also 2 Z elevators but the weight is practically on the leadscrews, so I don't think a very large rail would be needed (maybe a LM9?). I am not so sure about the Y axis, as it is horizontal and has to carry an aluminum Y car with the MK2 heated bed, an aluminum plate, and a build surface. Would a LM9 be enough? Maybe 12? Could I calculate it with a formula if I knew the weight of the components?

Thanks.

This site may help with capacities.
[www.pbclinear.com]

Look up elastic beam deflections equations. Once you know the mass, length, and area moment of inertia you can find the deflection. You can of course rearrange everything to find the moment of inertia required to meet your deflection tolerance.

I can't in good conscience read this thread and not recommend some good linear guides as an alternative to unsupported rods.

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epicepee
I can't in good conscience read this thread and not recommend some good linear guides as an alternative to unsupported rods.

That's exactly why I have posted this. I am trying to choose the right size of linear guides to replace my unsupported rods.

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drmaestro

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epicepee
I can't in good conscience read this thread and not recommend some good linear guides as an alternative to unsupported rods.

That's exactly why I have posted this. I am trying to choose the right size of linear guides to replace my unsupported rods.

Ah, sorry, I misunderstood.

Most linear guides are massively overqualified. MGN9 (9mm) rails can take thousands of Newtons, and yet most people use 12mm rails just because they're more available. Find one that looks reputable and cheap and you'llbe fine.

Keep in mind that the narrower the rail the more it can flex. In the X carriage anyway.