Patent ID: 8727677

Claim:
A boring method for boring a workpiece by a boring apparatus, the boring apparatus comprising a base on which a workpiece having a through-hole is placed, a cutting tool to be inserted through the through-hole of the workpiece, a rotary drive device configured to rotate the cutting tool, and a support jig configured to support the cutting tool by a bushing face, the cutting tool including a tool body having a main flow path extending along a length direction of the tool body and a branch flow path extending from the main flow path to an outer circumferential surface of the tool body, and a cutting blade provided on the outer circumferential surface of the tool body, the boring method comprising: forming a concave pocket on the outer circumferential surface of the cutting tool, at a part which faces the bushing face of the support jig and to which the branch flow path is opened, over an area that is larger than an opening area of the branch flow path; forming the branch flow path such that a binding member having an orifice that communicates an upstream side of the branch flow path with a downstream side of the branch flow path is detachably mounted in the branch flow path; preparing a plurality of binding members which differ from one another in diameter of the orifice; mounting the plurality of the binding members in the branch flow path by sequentially replacing the binding members; measuring a pressure of the fluid before passing through the orifice by removing a first insert plug that has been blocking the main flow path at an end of the main flow path and by attaching a pressure gauge to the main flow path, and measuring a pressure of the fluid after passing through the orifice by removing a second insert plug that has been blocking a support jig flow path formed in the support jig from the busing face to an exterior and by attaching a pressure gauge to the support jig flow path; selecting one of the plurality of the binding members, which has a ratio between the pressure of the fluid before passing through the orifice and the pressure of the fluid after passing through the orifice, which is closest to a predetermined ratio value, and mounting the selected binding member in the branch flow path; and supplying a fluid to the main flow path of the cutting tool thereby supplying the fluid between the outer circumferential surface of the cutting tool and the bushing face of the support jig through the main flow path and the branch flow path, and rotating the cutting tool while a hydrodynamic bearing is formed between the cutting tool and the support jig, so as to bore the workpiece.