A polishing system includes a platen having a top surface to support an annular polishing pad, a carrier head to hold a substrate in contact with the annular polishing pad, a support structure extending above the platen and to which one or more polishing system components are secured, and a support post. The platen is rotatable about an axis of rotation that passes through approximately a center of the platen. The first support post has an upper end coupled to and supporting the support structure and a lower portion that is supported on the platen or that extends through an aperture in the platen.