A machining process with significantly higher cutting speeds than conventional machining can enhance surface finish, machining productivity, and tool life. However, it also results in increased cutting temperatures, which can impact the surface quality of workpiece and the life of cutting tool. This study explores the effects of cutting speed (100–550 m/min), feed rate (0.01–0.2 mm/tooth), and cutting depth (0.2–0.5 mm) on the surface roughness of parts machined on a milling CNC machine. The experiment used carbon steel C45 as the workpiece material, a carbide face milling as the cutting tool, and soluble cutting oil as the coolant. The findings revealed that a rise in both the cutting speed and feed rate leads to an increment in surface roughness. However, these increases also lead to higher cutting temperatures, which can have implications on the life of the cutting tool and the quality of the surface that has been machined. This research is crucial for choosing appropriate cutting parameters to achieve the desired surface roughness and ensure efficiency in high-speed machining applications. Furthermore, the research findings contribute to broadening the understanding of machining and material processing.