Method and apparatus for making through-bores

摘要

The invention relates to a method and apparatus for marking entrance and exit opening sites in opposite surfaces of a wall member of a perforation to extend therethrough and is provided, at one surface at a site corresponding to one of the entrance and exit openings with a wave signal transmitter and, at the other surface with a wave signal receiver responding to transmitted signals by rendering an indication of a maximum strength wave signal as a function of the location of the other of the entrance and exit opening. In a preferred embodiment, the receiver is mounted on a drill or the like at a predetermined distance from the axis thereof and the transmitter is provided with a cantilever provided with a marker spaced from the transmitter at a distance corresponding to the predetermined distance.