| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem that a substrate sash exposed from a circular hole made in a ceiling plate must be cleanly removed along an inner circumferential surface of the circular hole in fitting a luminaire to a ceiling surface, and the removing work has been manually sawed by a metal saw. SOLUTION: A circular folded part 14 is formed at the position offset by a predetermined depth toward the center direction from an outer circumferential edge of a circular blade base material 11, and an outer part of the folded part 14 is inclined in a tapered manner to the end by a predetermined angle to form an annular inclined surface part 15. A blade part 16 is formed on an outer circumferential part of the inclined surface part 15 to constitute a circular cutting blade. This circular cutting blade is fitted to an electric rotating tool. If the substrate sash is cut with the inclined surface part 15 facing the ceiling surface perpendicular thereto, the cutting line can be an elliptical arc having the curvature substantially same as the curvature of the inner circumferential surface of the circular hole in the ceiling plate, and the substrate sash can be cleanly cut along the inner circumferential surface of the circular hole by the power tool.
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