Parts of a metal lathe

Written by cassie damewood
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Parts of a metal lathe
A lathe is common sight in a machine shop. (Image by, courtesy of Paul Anderson)

Every machine shop has a metal lathe. Many metal industry workers consider it the most basic and important tool in the shop. It is used to cut or "turn" metal. As the piece of metal is rotated on the machine, the cutting tool itself, the lathe, remains stationary.

Parts of the Metal Lathe

The metal lathe parts consist of a chuck, tool post carriage, cross-slide, tailstock and thread-cutting lever (also known as the half nut).

The Chuck

The three-jaw chuck is standard on most metal lathes. Four-jaw varieties are available, but less common. It is one of the most recognisable parts of a metal lathe.

Attached directly to the drive mechanism of the engine lathe, the chuck rotates at adjustable speeds up to 6500rpm. Even though the chuck is self-centring, a dial indicator should be used when the piece of metal to be turned is placed in the chuck. This ensures the metal is straight before the process begins, which is important to check because most metal pieces are not perfectly symmetrical. Once the part dimensions are determined to be accurate, the chuck key is used to tighten it into place.

The Tool Post Carriage and Cross-slide

The depth of the cut in the part being turned is controlled by the dial handle on the cross-slide of the carriage where the tool post is mounted. Each line on the tool post handle dial, depending on the lathe model, is equal to either 1/1000-inch or 2/1000-inch. There are two levers on the carriage. One lever feeds the carriage into the chuck at a predetermined speed. The other lever moves the cross-slide. To prevent damage to the carriage and cross-slide parts, apply a water-soluble oil mixture or light cutting oil to the keep the machine and the part being turned from overheating.

Tail Stock

Attached at the opposite end of the engine lathe from the chuck is the tail stock. The tail stock's most common function is to drill out the centre of the piece of steel begin turned. It uses a chuck much like that in a hand drill to accomplish this.

Thread-cutting Lever

There is a handle on the carriage called the thread-cutting lever, or half nut. It consists of a dial on the back of the carriage that has odd and even numbers on it to control the threading. This metal lathe part is highly sensitive to rpm speed of the rotating part. Directions for using this feature should be explicitly followed.

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