In the machining of stone–plastic composites, the cutting efficiency and increased economy are important considerations. To this end, stone–plastic composite was up-milled using tapered cutters. Cutting forces and temperature were measured under varied angle geometries and cutting parameters. Response surface methodology allowed the analysis of changes in cutting forces and temperature, and the significant contributions of each variable and their two-level interactions were determined. Correlations between actual and predicted results were found by developing mathematical models for cutting forces and temperature, which can be used to make accurate predictions. Finally, the optimisation of cutting conditions for tapered milling stone–plastic composites by minimising cutting forces and temperature was determined as taper angle 75°, feed per tooth 0.44 mm and cutting depth 0.5 mm. It is proposed that these parameters be adopted in industrial machining for higher machining efficiency and lower production cost.