The effects of pilot hole geometry on tool-work engagement efficacy in deep hole drilling

Deep hole drilling using single-lip drill (SLD) without a starting bush induces a severe cutting edge chipping if the pilot hole profile is not selected properly. In this paper, a new parameter 'Engagement Ratio' (ER) is introduced to determine appropriate pilot hole profile. ER depends on pilot hole and tool geometry combination. Application of ER is illustrated with geometrical model for four different engagement conditions. The range of values of ER for Inconel 718 was defined based on experimental results to ensure smooth engagement. Moreover, this approach can be extended to select the pilot hole geometry for other materials.