As a deep hole machining system, three systems, a gun drill system, RTA system and ejecting system, have been generally known. In a drill head used in the gun drill system, a V-groove for swarf ejection is formed throughout the whole length of a head body. In this system, high-pressure cutting oil is fed to a tip of a cutting blade through the inside of a shank of a drill, the swarf generated by the cutting blade is broken by the high-pressure cutting oil, and the broken swarf is forcibly ejected through the V-groove.
A drill head used in the BTA system is constituted by fixing a cutting blade to a tip surface of a head body attached to a tip of a pipe-shaped boring bar and fixing guide pads to a periphery of a tip of the head body. In this system, a casing in which a guide bush is built is arranged adjacently to an end surface of a material to be cut. Further, when cutting oil is pressurized and fed from an oil feeding port with end surfaces of the guide bush and the casing sealed with a sealing material, the cutting oil reaches the cutting blade from a gap between the boring bar and the guide bush through a gap between a cutting hole of the material to be cut and a peripheral surface of the drill head, flows into the boring bar from the cutting blade via a center through hole of the drill head, sweeps the swarf generated by the cutting blade away, and ejects the swarf from an ejecting port.
Additionally, a drill head used in the ejecting system is constituted by fixing the cutting blade to the tip surface of the head body attached to a tip of a shank constituted by a double tube which forms a cutting oil feeding path between an outer tube and an inner tube, and by fixing the guide pads to the periphery of the tip of the head body, and an opening which communicates with a hollow part of the inner tube is formed in the head body. In this ejecting system, most of the cutting oil fed from the oil feeding port of the casing during cutting goes out from an oil hole through the cutting oil feeding path between the outer tube and the inner tube, reaches the cutting blade through the gap between the cutting hole of the material to be cut and the peripheral surface of the drill head, flows into the inner tube from the opening, and a part of the cutting oil directly flows into the inner tube. Then, the inner pressure of the inner tube becomes negative, a pressure difference is generated, and an absorbing force is generated. Swarf is absorbed by a vacuum effect of the absorbing force and ejected from the ejecting port.
FIG. 3(a) is a side view showing a conventional drill head used in the BTA system and ejecting system, and FIG. 3(b) is an end view thereof. In FIG. 3, the reference symbol 1 denotes a hollow-shaped head body, a cutting blade 12 constituted by a single blade is fixed to the tip surface of the head body 1, guide pads 13 and 14 are fixed to the periphery of the tip of the head body 1, and the reference symbol 5 denotes a hole for ejecting swarf and cutting oil. FIG. 4(a) is a side view showing another conventional drill head similarly used in the BTA system and ejecting system, and FIG. 4(b) is an end view thereof. In FIG. 4, cutting blades 12a, 12b, and 12c, which constitute a divided blade, are fixed to the tip surface of the head body 1, and the guide pads 13 and 14 are fixed to the periphery of the tip of the head body 1.