Abstract: A hand-sized, compact tool utilized to cut a ninety degree notch in the edge of sheet material, such as an acoustic ceiling tile, in one easy motion. The tool is designed with a rounded outer surface that is ergonomic and may be fabricated from high density plastic or metal material. The tool employs a pair of standard cutting blades having cutting edges oriented perpendicularly to each other. The tool's unique design assures safety in that the cutting edges are positioned inside a guide groove and are thus, unexposed. Comprising only three parts, the tool may quickly and easily be disassembled to replace worn or broken cutting blades.