Low cost magnetic coating thickness gauge with holding magnet, bias

Abstract

A low cost magnetic gauge that measures the thickness of non-ferrous coatings such as paint on ferrous materials such as auto bodies. Construction consists principally of two telescoping tubes, connected by a spring, with a permanent magnet at the end of one tube. In operation, the magnet tube is placed against the surface being tested, and the other tube is pulled away from the surface. In a first embodiment, indicia are exposed as the non-magnet tube is pulled away, the reading being the last number exposed before the magnet tube pulls off the surface. A second embodiment employs a ratchet to hold the tubes apart at their maximum extension to facilitate reading. A third embodiment uses a wedge for the same purpose. A fourth embodiment adds a member which is drawn along the non-magnet tube by the magnet tube, and stays at its furthest extension on the non-magnet tube, due to a slight frictional load, when the magnet tube pulls off the material being tested. This embodiment permits recording of the reading, and fast one-hand operation of the gauge. The structure of this invention permits manufacturing costs far below any current coating thickness gauges.