Reaming is a process which slightly enlarges a pre-existing hole to a tight tolerance diameter. The geometry of a hole drilled in metal by a twist drill may not be accurate enough and may not have the required smooth surface finish for certain engineering applications. Reaming is therefore needed to remove a very thin layer of stressed and disturb material caused by drilling a hole.
Reaming can be done by hand or machine. The tip of a reaming tool is called reamer. A typical reamer is similar to a mill bit. It 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. Common types of reamers include Adjustable reamer, Straight reamer, Rose reamer, Shell reamer, Tapered reamer, and Combination reamer.