An appropriate and optimum machining parameters setting is crucial during machining operation in order to enhance the surface quality. The best composition type of geopolymer has not been investigated yet. Fly ash has been used in previous study but RFG material has not been used yet. This study will be used RFG material as the reinforcement material due to the increases number of waste tyres in Malaysia. The objectives of this research are to determine the best combination parameters and to analyze the most significant factor of machining RFG in producing the best surface roughness in CNC milling operation. The milling parameters evaluated are cutting speed, feed rate, and depth of cut. L9 Taguchi orthogonal arrays, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) are employed to analyze the effect of these cutting parameters. The analysis of the results indicates that the optimal cutting parameters combination for good surface finish is low cutting speed, high feed rate, and low depth of cut. The best combination of parameters obtained is cutting speed (30 m/min), feed rate (240 mm/min) and depth of cut (0.5 mm). The most significant factor affecting surface roughness on the machining is feed rate which was 50.44 %. The result for the confirmation test shows the average value of surface roughness contributed from the experiment was 0.9427 μm.
