I've got several reasons for that. Steel is "springier" than
concrete. You should get more vibration the way you describe. Also,
the coeffecient of expansion of concrete is essentially zero. Steel
will expand/contract with temprature.

A couple of things to consider.

1. As a material, steel is less "springy" (stiffer) than concrete. Young's
modulus of Steel is around 30,000,000 psi, concrete is around 5,000,000 psi.

2. The coefficient of thermal expansion for concrete is quite similar to that
of steel according this website:

http://www.tfhrc.gov/pavement/pccp/thermal.htm

"The CTE of Portland cement concrete (PCC) ranges from about 8 to 12
microstrains/°C"

Steel is around 10 microstrain/°C

----------

Whether the stucture that is built will be as stiff depends on the design,but
certainly a steep pier can be built that is sufficiently still, the only mode
that is of concern in bending and that a steep column can be plenty stiff. A
properly designed steel column ought to be signifcantly more solid that a
moveable tripod.

As far as the need to have the top of the mount level, as I understand it, this
is not necessary for proper tracking.

From a design point of view, I think it would be wise to do any leveling at the
top of the pier rather than the bottom, though if things were robust it would
not matter. The leveling mechanism could reduce the stiffness of the system.

As far as using a "wedge", I agree that one would be better off with a simple
angled plate or some such thing. Wedges are designed to allow wide ranges of
adjustment which in your case is unneeded.

Jon Isaacs