Abstract: A cutting instrument has a cutting blade portion formed with a skin made of an electrode material or a reaction product of the electrode material, the electrode material having been molten by pulse discharges induced between the cutting blade portion and an electrode in a machining liquid or gas, having as the electrode one of a mold molded from powder of a kind or powder of a mixture of kinds out of a metal or metals, a metal compound or metal compounds, and a ceramic or ceramics, and a heat-treated mold being the mold as heat-treated.

Abstract: A cutting instrument (1) has a cutting blade portion (13) formed with a skin (7) made of an electrode material or a reaction product of the electrode material, the electrode material having been molten by pulse discharges induced between the cutting blade portion (13) and an electrode in a machining liquid or gas, having as the electrode one of a mold molded from powder of a kind or powder of a mixture of kinds out of a metal or metals, a metal compound or metal compounds, and a ceramic or ceramics, and a heat-treated mold being the mold as heat-treated.

Abstract: There is provided a cultivator blade supporting structure including at least one cultivator blade having a shank and a blade portion, at least one blade holder having a cavity for removably receiving the shank of the cultivator blade, and a rotational driving shaft to which the blade holder is fixed, wherein at least a part of the cavity is defined by first confronting oppositely inclined interior surfaces and second confronting oppositely inclined interior surfaces which have a different inclination angle from the first inclined interior surfaces, so that contact portions of the shank are wedged between and into the first and second inclined interior surfaces when the rotational shaft rotates to cultivate the ground.

Abstract: There is provided a cultivator blade supporting structure. The structure comprises at least one cultivator blade comprising a shank and a blade portion; at least one blade holder having a hollow sleeve for removably receiving the shank of the cultivator blade; and a rotational driving shaft to which the blade holder is fixed, wherein at least a part of the sleeve for receiving the shank of the cultivator blade comprises confronting oppositely inclined interior faces between which the shank is wedged when the cultivator blade is rotated to cultivate the ground.