Lathe Machine Operations – Plain Turning or Straight Turning

Plain Turning or Straight Turning. The work is turned straight when it is made to rotate about the lathe axis, and the tool is fed parallel to the lathe axis. The straight turning produces a cylindrical surface by removing excess metal from the work piece. After facing the ends and drilling the centre, the job is carefully mounted between the centres using a lathe dog attached to the work piece. A properly ground right hand turning tool is used for this purpose. Tool is clamped on the tool post with the minimum overhang and is set with its cutting edge approximately at the lathe axis or slightly above it. For light cuts the tool may be inclined towards the headstock, but for heavy cuts the tool must be inclined towards the tailstock. The automatic feed is engaged to move the carriage to the desired length, then the feed is disengaged and the carriage is brought back to the starting position. The process is repeated until the job is finally finished.

There are two kinds of cuts that can be given onto a work piece: Rough Turning & Finish Turning

rough turning operation

Rough Turning.    The rough turning is the process of removal of excess material from the work piece in a minimum time by applying high rate of feed and heavy depth of cut. The roughing cut should be so made that the machine, the tool, and the work piece can bear the load. The depth of cut for roughing operations in average machine shop work is from 2 to 5mm and the rate of feed is from 0.3 to 1.5 mm per revolution of the work. Rough turning operations are carried out by rough turning tool.

Read more about   Machine Tool Basics - Lathe Cutting Tools

Finish Turning. The finish turning operation requires high cutting speed, small feed, and a very small depth of cut to generate a smooth surface. A finish turning tool having sharp cutting edge is held securely on the tool post for this purpose. In finish turning operation, the depth of cut ranges from 0.5 to 1 mm and feed from 0.1 to 0.3 mm per revolution of the work piece. The cross feed dial is used to set an accurate depth of cut. After measuring the diameter of rough turned surface, the depth of cut to be given is determined by subtracting the finished diameter from the measured value. The tool is then made to advance by half of the above value by rotating the cross slide hand-wheel through required number of divisions on the dial. The machine is started and a trial cut is made from the end of the work to 5 or 6 mm by applying hand feed and the finished diameter is checked by a micrometer. Once the correct diameter is made, the rest is finished by the automatic feed.