Reamer

A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precision reamers which are used for more basic enlargement of holes or for removing burrs. The process of enlarging the hole is called reaming. There are many different types of reamer and they may be designed for use as a hand tool or in a machine tool, such as a milling machine or drill press.

A typical reamer consists of a set of parallel straight or helical cutting edges along the length of a cylindrical body. Each cutting edge is ground at a slight angle and with a slight undercut below the cutting edge. Reamers must combine both hardness in the cutting edges, for long life, and toughness, so that the tool does not fail under the normal forces of use. They should only be used to remove small amounts of material. This ensures a long life for the reamer and a superior finish to the hole.

The spiral may be clockwise or counter-clockwise depending on usage. For example, a tapered hand reamer with a clockwise spiral will tend to self feed as it is used, possibly leading to a wedging action and consequent breakage. A counter-clockwise spiral is therefore preferred even though the reamer is still turned in the clockwise direction.

For production machine tools, the shank type is usually one of the following: a standard taper (such as Morse or Brown & Sharpe), a straight round shank to be held by a collet, or a straight round shank with a flat for a set screw, to be held by a solid toolholder. For hand tools, the shank end is usually a square drive, intended for use with the same type of wrench used to turn a tap for the cutting of screw threads.

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