The Union Butterfield 4531 high-speed steel straight flute expansion chucking reamer (also called a machine reamer) is an uncoated (bright) round shank tool with a 45-degree bevel lead, commonly used for reaming of uninterrupted cuts in high-production runs on abrasive materials. An expansion reamer can be expanded using a screw in the center of the reamer as wear decreases its cutting diameter, so it can be reground to its original dimensions and re-sharpened to prevent rapid loss of reamer size or finish. This tool can be used in a drill press, screw machine, or lathe, or other good-quality toolholders.

Straight flute reamers make small, circular, and precise enlargements to through and blind holes. They can be used on a wide variety of materials. Round shanks aid accurate centering; they are designed to be held in a chuck or collet for high-torque applications. High-speed steel (HSS) is a general-purpose steel for cutting tools that is compatible with many metalworking materials, and is often lower in price than other cutting tool substrates. This reamer has a 45-degree bevel lead at the cutting tip to facilitate entry to pre-drilled holes.

In the Union Butterfield 4531 series, reamers 0.3750” to 0.9688” in diameter have six flutes, 1.0000” to 1.3750” in diameter have eight flutes, 1.4375” to 1.8125” in diameter have ten flutes, and 1.8750” to 2.0000” in diameter have 12 flutes. Tolerances for 0.3750” to 1.0000” reamers are +0.0001” to +0.0005” and tolerances for 1.0312” to 2.0000” reamers are +0.0002” to +0.0006”.

Reamers are used to finish existing holes. When holes are created using common applications such as drilling or punching, they often have minute imperfections. Their roundness may be flawed, or their diameters may be slightly smaller than required. Reamers are made to exacting tolerances so they can correct such errors and create precisely round holes with exact dimensions. Reaming is often used before tapping screw threads.

Precision manufactures machine tools under the following brands: Precision Twist, Precision Dormer, and Union Butterfield. They have locations around the world, and provide tools adhering to ANSI, NAS, and DIN standards.