A theoretical and experimental investigation of coolant flow in gundrilling

Abstract The basic gundrilling concept and desirable characteristics of coolant in gundrilling are presented. From the measurements of effective cross-sectional areas at the interface of the ν-shank and the tip for three types of gundrill, the small diameter drills did not show a marked difference in their effective areas. For large diameter drills, the two-hole drill claims maximum effective area. The percentage reduction of cross-sectional area in the case of two-hole tip is high for small diameters whereas for large sizes, it is negligible. Experiments on three types of drills were carried out by connecting them in a closed pressurized hydraulic circuit under identical inlet and environmental conditions. For the same inlet pressure, the energy loss was maximum for the one-hole and minimum for the two-hole. To achieve the same Reynolds number, the two-hole drill showed the least energy loss. The results from the theoretical analysis showed a similar trend to those of experimental ones. A high variation between the two at high pressure was noted.