PURPOSE: To obtain a strong and semi-permanent further easily manufactured filtering body of cutting oil, by forming one side end face of narrow slit holes to a vertical face and the other side end face to a sloped face opening to spread in the bottom then an inlet of the slit narrow while its outlet to an open and spread shape.

CONSTITUTION: An upper metal mold 1, in which the bottom face of an angular pillar is recessed to a firmly-set mouth shape and a sloped face 1' and a point end edge successively provided to the sloped face 1' are formed to an edge part 1", is used in suitable places in the bottom part of a conveyer chute. And an angular hole 2 is extensibly provided in the vertical direction toward the center of the angular pillar, while an upper face of the angular pillar is recessed to a horizontal doglegged shape throughout to a center side end edge of the hole 2 and formed to a sloped face 3' coincident with a tilt angle of the sloped face 1' formed to the mold 1, further a bottom metal mold 3, in which an outside end edge of the hole 2 is formed to an edge part 3", is used. Then the conveyer chute is sheared by the edge parts 1", 3" by press work, while a cut place is folded to a firm-set mouth shape by the sloped faces 1', 3', and narrow slit holes 4 are formed between the vertical sheared face and folded point end face. In this way, an inlet of the hole 4 is formed narrow while its outlet is formed to an opening spread shape by a sloped face 5.