Lathes perform the machining operation known as "turning." In turning, material is removed from a workpiece by rotating it against a tool. Turning is an important manufacturing operation in the production of many metal, plastic and wood parts. Lathes can be either manually operated or computer controlled (CNC). Lathes can have have many variations, special features and attachments to facilitate a wide range of jobs.
The simplest lathe type is the wood lathe. As the name suggests, it is designed for turning wood. Wood lathes are small machines consisting of a bed, headstock, tailstock and tool rest. There are no precision ways as are found on a metal-working machine, since the cutting tools are moved by hand and not by machine power. Great skill is needed to control the cutting tool to accurately turn smooth curves and complex contours on the work piece.
The spindle is usually driven by a belt connected to a motor, and speed changes are made by manually moving the belt to one of several pulleys mounted to the back of the spindle.
Lathe tools are held manually against the work, with the support of the tool rest. The tool rest is adjustable and is clamped to the bed at a position convenient for the operation at hand.
Engine lathes are the classic metal turning workhorses of the production machine shop. They come in many sizes and are adaptable to working virtually any material. These machines have a longitudinal bed to which is mounted a headstock and tailstock.
As in the wood lathe, the headstock contains the spindle. However, the spindle drive is more complex, including variable speed capability or selectable gearing to provide a much wider range of speeds.
A carriage moves back forth on bed ways for longitudinal turning. A cross-slide and compound rest are mounted to the top of the carriage to provide cross and angular cutting capability.
The lathe cutting tools are moved against the work manually using hand wheels or automatically under the power of a lead screw that is driven by gears in the headstock.
The tool room lathe is a small- to medium-sized engine lathe specially designed for high-precision work. These machines find use in tool and die shops, where custom parts and precision fixtures are produced, often in support of production machining operations.
Tool room lathes are manufactured with special attention to spindle accuracy, smooth operation and precise alignment of the carriage and cross slide. A tool room lathe is capable of better accuracy and precision than a standard engine lathe.
Turret lathes are used in production machine shops where several sequential operations are needed on single workpiece. It is costly and time consuming to remove a workpiece from one machine and hold it in another. Removing and reholding a workpiece also introduces errors in work alignment and machining accuracy.
The turret lathe has a rotating turret mounted to the carriage so that as soon as an operation with one tool is completed, the turret is indexed to bring another tool into working position. The part is then machined again without having to remove it from the chuck or collet. Eight (or more) different operations can be performed on a workpiece using this type of machine.
Computer numerically controlled lathes have largely supplanted engine lathes in production machining environments. CNC lathes offer the advantages of greater powered axis drives, feedback control to monitor and maintain tool positioning and high-speed repeatability of complex machine motions. Once a program is verified, an operation can be quickly set up again without the need for tedious manual adjustments.
CNC lathes excel at cutting curved contours without the need for specially shaped tools. This is done by programmed variation of the speed of two motion axes and the spindle simultaneously---an operation that is impossible with an engine lathe.
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