Main purpose of this research to investigate the effect of the main factors of the surface roughness in AISI P20 Steel end milling. The results of the research could be applied in the manufacture of automotive components and mold industries. This study was conducted by using CNC end milling machine with 8 mm diameters fine type carbide tool with twin cutting tip. The controlled factors were the speed, the feed rate and the depth of cut. For this experiment, we used Taguchi design with L16 Orthogonal Array and the result showed that the factors effected of surface roughness was the cutting speed is most influence factors affect the surface roughness. Furthermore, the surface roughness was likely to reduce when speed was 3000rpm and the feed rate was 1000mm/min and Depth of cut 0.8mm The result of the research led to the linear regression equation measurement value which was Ra = 6.760 - 0.946 Cutting speed –0.204 Depth of Cut – 0.368 Feed rate. The equation formula should be used with the speed in the range of 1200 - 3000rpm, rate of feed in the range of 1000 - 2500mm/min and the depth of cut 0.2 - 0.8. The equation was used to confirm the research results, it was found that the mean absolute percentage error (MAPE) of the surface roughness obtained from the predictive value comparing to the value of the experiment was 4.87%, which was less than the specified error and it was acceptable.
