GRINDING STONE

To provide a grinding stone for hole-processing having abrasive grain fixed onto a base material, which can grind a center part of a bottom of a processing hole flatly, without making the abrasive grain adhere to a shaft center on a tip surface of the grinding stone.SOLUTION: A grinding stone 100 comprises a shaft body 1 and a grindstone layer 5 having abrasive grain fixed to a tip side of the shaft body, which makes the tip of the shaft body rotating around an axis form a hole with a bottom on a work-piece, which further has a pair of flat surfaces 6 and 7 which are orthogonal to an axial direction of the shaft body and are formed point-symmetrically with a center O of the shaft body as a center, on a surface of the tip of the shaft body, and a pair of first inclined surfaces 10a and 11a which are formed point-symmetrically with the center of the shaft body as a center and are formed continuously on the flat surfaces, where edge parts of the pair of first inclined surfaces inclined in opposites directions cross each other at the center of the shaft body.SELECTED DRAWING: Figure 1 【課題】母材上に砥粒を固定した孔加工用の研削砥石において、砥石先端面の軸中心に砥粒を付着させず、加工孔の孔底中心部を平坦に研削することができる砥石を提供する。【解決手段】軸体１と、前記軸体の先端側に砥粒を固定する砥石層５とを備え、軸回りに回転する前記軸体の先端によって、被加工物に対し有底孔を形成する研削砥石１００であって、前記軸体の先端面において、前記軸体の軸方向に直交するとともに、軸体中心Ｏを中心として点対称に形成された一対の平面部６、７と、前記軸体中心を中心点として点対称に形成され、前記平面部に連続して形成された一対の第１の傾斜面１０ａ、１１ａとを有し、傾斜方向が逆となる前記一対の第１の傾斜面の縁部は、前記軸体中心において交差する。【選択図】図１