<Dd> Note: All units must be converted to the corresponding decimal (or USCU) units . </Dd> <P> Machining operations usually divide into two categories, distinguished by purpose and cutting conditions: </P> <Ul> <Li> Roughing cuts </Li> <Li> Finishing cuts </Li> </Ul> <P> Roughing cuts are used to remove large amount of material from the starting workpart as rapidly as possible, i.e. with a large Material Removal Rate (MRR), in order to produce a shape close to the desired form, but leaving some material on the piece for a subsequent finishing operation . Finishing cuts are used to complete the part and achieve the final dimension, tolerances, and surface finish . In production machining jobs, one or more roughing cuts are usually performed on the work, followed by one or two finishing cuts . Roughing operations are done at high feeds and depths--feeds of 0.4--1.25 mm / rev (0.015--0.050 in / rev) and depths of 2.5--20 mm (0.100--0.750 in) are typical, but actual values depend on the workpiece materials . Finishing operations are carried out at low feeds and depths--feeds of 0.0125--0.04 mm / rev (0.0005--0.0015 in / rev) and depths of 0.75--2.0 mm (0.030--0.075 in) are typical . Cutting speeds are lower in roughing than in finishing . </P>

The first step in machining raw material after loading the material is known as