Spiral-Edge Countersinks: One Curved Slot Up the Cone Makes an Edge That Slices Instead of Scraping (Laursen, 1926)

Laust K. Laursen of College Station, Texas, received US 1,586,559, dated 1 June 1926. Ordinary countersinks have straight edges in radial planes, which press on the wood all at once and scrape it, like pushing a knife straight down on a loaf. Laursen curved the edge into a spiral running up and out from near the point, ahead of the radial line as the tool turns. It reaches the wood a little at a time and slices, leaving a smooth countersink without chatter. His simplest form is one curved slot in the cone, its leading edge sharpened and the cone behind it relieved. We make a set of three in tool steel. The patent gives no sizes; every size here is ours.