  A Cassegrain mounted adaptive optics instrument presents unique challenges
for opto-mechanical design. The flexure and temperature tolerances for
stability are tighter than those of seeing limited instruments. This criteria
requires particular attention to material properties and mounting techniques.
This paper addresses the mechanical designs developed to meet the optical
functional requirements. One of the key considerations was to have
gravitational deformations, which vary with telescope orientation, stay within
the optical error budget, or ensure that we can compensate with a steering
mirror by maintaining predictable elastic behavior. Here we look at several
cases where deformation is predicted with finite element analysis and Hertzian
deformation analysis and also tested. Techniques used to address thermal
deformation compensation without the use of low CTE materials will also be
discussed.
