[Qbot2640]

Originally Posted by Tottanka

im planning on a 3/8'' dead shaft, for a 6x6 or 8x8 DT.
is that a problem in your opinion?

There are many variables to consider: total load, length of shaft from support to load, Modulus of Elasticity of the chosen material, etc. But the comparison of section modulus in 3/8" round to 1/2" round (and to 1/2" hex) is rather surprising.

3/8" Round has a section modulus of 85mm^3
1/2" Round has a section modulus of 202mm^3
and 1/2" Hex has a section modulus of 213mm^3

We have bent 1/2" steel round in a non-drivetrain robotics application, and we have bent 1/2" bolts used as dead axles supported on both sides of the wheel (estimate 5" spacing)...this comparison would make me very hesitant to use 3/8"

Sources:

http://67.237.145.72/PDFs/SECTIONPROPERTIES.pdf
http://www.engineersedge.com/calcula...re_case_15.htm