On Tue, 28 Nov 2006 22:49:39 -0000, "Autolycus"
wrote:


"T i m" wrote in message
.. .

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).

Ah, cheers!

So (just to make sure understand your results) the 1/2" bar will be
~3x stiffer than the 3/8" one ??

All the best ..

T i m