The watermelon mill is used in running the sidetracking system.
API standard

Description:

The watermelon mill is used in running the sidetracking system. The watermelon mill is used in the same string with the window mill for smoothing and cutting clearance in the pack-stock window. The string mill is then added to the string with the taper mill and watermelon mill to make a stiffer cutting assembly and further open the window for subsequent drilling operation. once again the mill is dressed with tungsten carbide material.