The paper presents an experimental study on the workspace and force requirements for general craniotomy tools and introduces a new manipulator for a craniotomy robot that is optimized to meet these requirements. The craniotomy is a surgical technique that allows the surgeon to access organ (brain) inside the skull. Surgical drill and cutter are used to open the skull prior to the neurosurgery. The technical requirements of this application are studied through discussion with medical personnel, observation of the real operation, and experimentations. The surgical tool has been instrumented and used on animal bones to collect clinical data including cutting force and motion range. A serial spherical arm is adopted for the present application, and its kinematic and force transmission indices are defined to identify an optimal mechanism through two different optimization methods. Last, a computer-aided design model of the optimized robotic manipulator for craniotomy application is presented.