Abstract: A powered circular saw blade on a vertical shaft is supported on a slide which is slideably mounted on a guideway having feet to enable moving the assembly around on a building sub-floor. The feet are adjustable to enable raising or lowering the guideway base and, thereby, the saw blade. A blade guard is affixed to the guideway base and shaped to admit the saw assembly to an inside corner of a building room. The blade is normally retracted behind the blade guard but can be advanced to position ahead of the guard as the guard is braced against a door jamb or the like and the slide is pushed toward the door jamb to advance the blade into cutting position. Immediately upon release of the advancing force manually applied, a return spring returns the blade to retracted protected position.