Bone machining is a common procedure in a majority of orthopaedic surgeries. Machining parameters including spindle speed, feed rate, type of power system (pneumatic and electric) and tool design significantly influence the surface properties of the bone. Surface characteristics such as roughness (average and roughness gradient) and thermal damage due to heat generation (thermal necrosis) determine the success and rate of rehabilitation of these surgeries. Further, pneumatic systems experience significant change in spindle speed during the process of machining. This study aims to understand the influence of dynamic spindle speed in pneumatic systems during machining action at various feed rates, on the surface roughness of the machined features of a porcine fibula. Results of this study will contribute to a better understanding of the dynamics of machining an anisotropic material like bone and will help investigate the need to develop a closed-loop system based on varying spindle speeds during the operation.