Machine Tools

Lathes are considered to be one of the oldest machine tools in existence. Lathes were typically foot-powered until water and steam power were harnessed. One of the first machines driven by Watt's steam engine was a lathe which is how it came to be known as an "engine lathe." The lathe operates by holding the workpiece in a rotating holder, usually a chuck or collet, and then a single-point cutting tool is fed into the workpiece. If the tool is fed along the axis of rotation of the workpiece, it is considered to be a "turning" operation and any desired cylindrical contour can be made. If the cylindrical contour is produced on the inside of the workpiece, the operation is called "boring." In addition to turning and boring, the lathe is also used for threading, tapping, facing, tapering, drilling, reaming, polishing, and knurling. Some typical parts a lathe may produce are pins, bolts, screws, shafts, discs, pulleys, and gear blanks. Different attachments allow a lathe to perform milling, grinding, and broaching operations. With the right combination of attachments, it is said that the lathe is the only machine tool capable of reproducing itself. The size of a lathe is given in terms of the maximum "swing" and length of bed. The swing refers to the maximum diameter of work which can be rotated in the lathe. The length of the lathe bed refers to the maximum length of the lathe ways, not the maximum distance between centers of the chuck and tailstock. Many different varieties of lathes are available ranging from the small precision lathe used for making watch parts to the extremely large lathes used in producing mill rolls and rocket casings.

Lathes can generally be classified in one of the following five basic groups: engine lathes, speed lathes, turret lathes, vertical lathes, and automatics. The engine lathe, sometimes referred to as a "geared-head" lathe, is the most commonly found lathe model. Speed lathes are used where the workpiece is polished or formed (e.g., spinning) rather than cut. Turret lathes have a "turret" tool changer which rotates to permit a number of different tools to be used in a certain sequence. Vertical lathes have a vertical axis of workpiece rotation rather than horizontal. Automatic lathes consist of high production turning machines such as screw machines and single or multiple spindle chucking and bar fed machines. All of the five basic lathe groups can also be found in a computer numerically controlled version, sometimes called a "turning center." The main components of a typical engine lathe include the following: bed, headstock, feedbox, tailstock, and carriage. The bed is the base of the lathe that supports the other components. The precision ways are the part of the bed on which the carriage travels. The bed is a massive casting in order to absorb and dampen vibration from the machining process. The headstock is mounted rigidly on the bed and houses all the gearing and mechanism for the spindle drive and power takeoff source for the feedbox. Controls for selecting and changing spindle speeds are also part of the headstock. The feedbox, which may be an integral part of the headstock or a separate unit, drives both the feed rod and the lead screw for the feed rate or thread lead required.

A direct mechanical connection with the spindle drive is required to provide the proper relationship for feeding or threading operations. The lead screw is a precision part and is usually only used for threading operations to avoid unnecessary wear.

Most engine lathes incorporate a feed rod which is used to drive the carriage for operations other than threading. The headstock spindle supports a faceplate, chuck, or collet, which in turn holds and drives the workpiece. There are four types of standard spindles, all identified by the type of nose: threaded nose, camlock, taper nose key drive, or flanged nose. The threaded nose spindle is usually only found on smaller and less expensive lathes. The camlock type allows faster changing of faceplates or chucks. The taper nose key drive type provides greater support to the workpiece while the flanged spindle nose permits mounting of special chucks or power operated equipment and can be found on turret lathes and automatics. The tailstock is mounted on the bedways and may be positioned and clamped to support work for turning. It may also use a tool mounted in place of the tailstock center so that boring, drilling, or reaming can be done. The tailstock must be perfectly aligned with the headstock spindle in order to produce good parts. The carriage is the tool platform of the machine and supports and feeds the cutting tool over the work. The carriage consists of the cross slide, which bridges the ways to support the compound and tool post, or toolholder, and the apron. The lead screw and the feed rod pass through the apron and transmit feeding power to the carriage. The main controls for positioning and feeding the tool are also located on the apron.