In the first part of this paper, geometrical relations were formulated to describe the geometry of a self-piloting drill with external chip removal. A novel approach to the design of the cutting tip was proposed and an experimental comparison between conventional and newly designed drills was made. In deep hole drilling, after the tool and the machine, the most important component is the coolant. It is important that the coolant be distributed uniformly within the machining zone to improve chip removal, lubrication and cooling. Thus, in this paper, the coolant flow in the limited space between the drill flanks and the bottom of the hole being drilled (called “bottom clearance”) is emphasized. Experimental investigations were done by using a specially designed workpiece which enables continuous monitoring of coolant flow and pressure distribution in the machining zone. The investigation shows that the newly designed drill is characterized by a significantly better coolant distribution in the bottom clearance resulting in an increase in tool life and better chip removal conditions.

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