AbstractThe primary objective of this research was to compare the surface finish resulting when using a semi‐synthetic cutting fluid to that of a premium soluble oil. The secondary objective was to determine the effects of drill diameter, cutting speed, and fluid concentration on surface finish.The surface measurements were made on the walls of 6.350 and 9.525 mm lind holes drilled 25.4 mm into aluminium 390. Each cutting fluid was introduced using a flood application. Additional factors in the experimental design for each cutting fluid included two levels of cutting speed and two levels of fluid concentration.Variations in drill diameter, cutting speed, and the interaction between these factors were significant with respect to surface finish for both the semi‐synthetic fluid and the soluble oil. Fluid concentration for the semi‐synthetic fluid also had a significant effect on the surface finish. The surface finish produced while using the semi‐synthetic fluid was approximately the same as that with the solu