3D Printing: Carbon fiber instead of smooth steel rods? (2 Solutions!)
Channel: Roel Van de Paar
Date: 2019-06-26

3D Printing: Carbon fiber instead of smooth steel rods?


The Question: I have a long 8 mm smooth steel rod of about 55 cm long. This rods bend easily
due to the length. If I replace them with 8mm solid carbon fiber rods, will the
bending reduce? Will the bearings wear off the carbon fiber rod? I couldn't
find too much information about this.

Solutions: Please watch the whole video to see all solutions, in order of how many people found them helpful

== This solution helped 10 people ==
Steel is the best material for a linear rod when you have a fixed cross-
section. It will have the least flex of any rod (aside from some exotic metals)
of the same size.
Carbon fiber's material properties might seem superior at first sight, but the
stiffness is very anisotropic -- it's very stiff along the grain and not very
stiff across the grain. So multi-axis stresses like bending aren't necessarily
going to perform up to the theoretical specs. Carbon fiber has exceptional
stiffness-to-weight ratio, but the stiffness-per-area isn't necessarily
superior in this application.
People do occasionally use carbon fiber for linear rods/rails, but only in much
larger sizes than 8 mm. Think ＞25 mm.
And that's really the problem here. 8 mm diameter at 550 mm long is well
outside what's reasonable for bending stiffness. Bending deflection increases
with the CUBE of length, and this is simply far too long for the size of rod.
The general rule of thumb for precision motion applications is length ＜
25*diameter. That's a conservative rule, but it's the right ballpark. You
really shouldn't be going over 200-250 mm or so with an 8 mm rod.

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