PURPOSE: To obtain an optimum cutting efficiency by taking a large hook angle, and reducing a rake angle, thereby suppressing a reaction force to an allowable range.

CONSTITUTION: A top plate angle is changed, and a reduce allowable side plate angle of 25 degrees is formed. Accordingly, an influence of an ellipse affecting to a hook angle HA is reduced. A position of a top 34 of a file 12 to a cutting edge 28 is lowered to set the angle HA to 30 degrees. The angle HA is obtained by drawing a line at one point of a side plate cutting edge 26 disposed down from a cutting end. Thus, a predetermined top plate cutter edge angle of about 25 degrees is obtained, and a lowering angle is set to 0 degree. When the angle HA is increased in the degree of allowing against a reaction force to provide a rake angle for allowing the top plate, an optimum cutter can be manufactured.