Drill Diameter Selection When Chamfering With respect to guide hole diameter D, select the drill diameter (cutting diameter) DC to be within the range of D < DC < 2D. OOKK NG NG DC D If DC is equal to or greater than 2D: If DC is a drill diameter equal to D: Example) If guide hole diameter D is .197": If drill diameter DC is too large Chamfering cannot be performed if Drill diameter DC should be equal to or compared to guide hole diameter drill diameter DC is the same as guide greater than .236" but less than .394". D (equal to or greater than 2D), hole diameter D. Select a DC of .236", .276", or .315". chamfering cannot be performed. When Centering The tool cannot be used for processing if the centering diameter has the same guide hole diameter as drill diameter DC. Refer to the usable length LU (page M172) as a guideline. In the region of roughly DC/4, which is the region of the two-step point angles, the central area will not have a 90° bottom hole angle. M DC/4 DC DC M173 LU PL DRILLING