Abstract: A broken bit detector for use in conjunction with printed circuit board drilling machines or the like. The detector includes a light emitter and a light sensor contained within a pressure foot. The light emitter projects a beam of light through a central opening in the pressure foot and toward the light detector. Normally, the beam will be broken by a drill bit which passes through the opening. If a bit is not present, the light beam will not be broken and will be detected by the photosensor. Pressurized air is forced outward from both the light emitter and light detector in order to prevent any chips created by the drilling operation from striking the emitter or detector. The use of the air creates a shield which results in an accurate detector having a long life.