The Alvord Polk 179-0 90 degree angle center reamer is a general purpose round shank tool made of high-speed steel with no finish or coating, and is most commonly chosen for chamfering the entry of a predrilled hole, and the conical part of the hole is then called a countersink. This tool can be used in a drill press, screw machine, lathe, or other good-quality toolholder. Countersinks, or center reamers, are manufactured with six common angles: 60 degrees, 82 degrees, 90 degrees, 100 degrees, 110 degrees, and 120 degrees. The most common of these are 82 and 90 degrees. High-speed steel is a general purpose steel for cutting tools and is compatible with many metalworking materials. It is often lower in price than other cutting tool materials. There are three flutes for all reamers in this series. Tolerances are plus or minus a half of a degree on the angle for all reamers in the 179-0 series. Center reamers are used to enlarge an existing hole at the entry of the hole in order to create a chamfer, in this case called a countersink. Countersunk holes are often intended to allow a screw’s head to be flush with the surface of the item being fastened. Center reamers probably obtained their name due to the use of a center reamer to clean out and refinish a “center,” which is simply a conical impression used for holding the workpiece, when machining “between centers.” Reaming positively affects the mechanical properties of the hole by producing a hole with an exceptionally smooth finish and very tight tolerance. 60 degree center reamers are used for machining between centers, 82 degree center reamers finish a hole for standard inch countersunk screws, 90 degree center reamers finish a hole for metric fasteners, and 100, 110, and 120 degree fasteners are typical countersink angles for rivets. Alvord Polk manufactures a broad family of cutting tools, brushes, and tooling components, following ISO 9001 standards for quality and environmental impact of their products. Their offices and manufacturing facilities have been located in the United States since 1881.
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