Two SAG mills at the CSA Mine Concentrator in New South Wales Australia were recently replaced and optimised using grindcurves as an operational tool. The mill upgrade included the exchange of the motor with a higher-power motor capacity including variable speed drives (VSD). The internal design of the shell lining was also changed to a skip row design with increased lifter spacings. After mill commissioning and start-up, grindcurves determined the optimum operating guidelines for throughput and product size for different circuit configurations based on mill filling, bearing pressure and power draw. A simplified 3-point grindcurve was also developed to facilitate the overall process, gain stability of the mill, and minimise production risks during low and high mill filling conditions. This 3-point curve was analysed with basic statistics and robust regressions for throughput and particle size. In overall, Mill 2 was optimised in approximately two months at different mill speeds, whereas Mill 1 took approximately nine months due to the need of readjusting bearing pressures after commissioning. This paper provides an overview of the metallurgical mill optimisation after commissioning.