On Sun, 25 Jul 2010 12:25:58 +0000 (UTC), des bromilow
wrote:

Hello Bob,

Basically I'm trying to remove the timber, and reduce the weight - the "tabletop"
is actually the top of a small shelf/ cabinet which holds the lathe.

By making the tabletop steel, I can weld things to the top, and drill and
tap fixtures as required - things I'd be less comfortable doing with wood
underlay.

I've got 4mm (just over 1/8") thick galvanised sheet that I plan on using
to replace the 12mm MDF.

If the properties says the 4mm isn't as "stiff" then I'll be putting some
braces or something in - but I'm trying to reduce the weight since I'm adding
other accessories such as VSD, taper turner, etc to the system.


You're looking for the modulus of elasticity of the materials, AKA
Young's modulus. All other variables held equal, deflection varies
inversely with the cube of the thickness. So the modulus of the steel
would have to be 27x (3x3x3) that of the MDF for equal stiffness.

Damping is also something to consider. You may get more vibration with
a thin steel sheet than with the MDF, even if the stiffness is the
same.

--
Ned Simmons