What is a live centre on a centre lathe?

The lathe is one of the machine tools most widely used in machining workshops, and it was the first machine invented for working metals. But for a lathe to work properly it must have certain tools and tooling that make it possible to produce quality workpieces.

The lathe and its operations

The lathe is a machine that can machine workpieces made of different materials such as metal, wood or glass. Turning operations include drilling, straight turning, facing, grooving, among others. Each of these processes has very particular characteristics, and in all of them machining is done by swarf removal or waste, which gives the workpiece being worked the shape you want.

This machine has a very wide range of uses. Lathes are found in the metalworking industry, producing parts that are later sent to other sectors such as automotive, manufacturing, food, aerospace and telecommunications; they are also used for artistic work.

Lathes are known for their versatility, since many different processes can be carried out on them, but also for their speed, accuracy and efficiency. It all depends on the model of machine used and on the right tools being used on it. One of the fundamental accessories for correct machining is the lathe centre.

The centre of the centre lathe

The lathe centre is a type of tooling used on these machine tools for the machining of metal and wooden workpieces. This part is essential on centre lathes, since its function is to shape or turn shafts of a given length.

The lathe centre is housed in the tailstock spindle of the lathe. The spindle is a sort of long, large-diameter screw used to operate the vices and jaws of the machine, and also to carry out the various movements of the lathe carriage. The chuck, to which workpieces are attached, sits on the spindle. The tailstock or movable headstock, generally found on the right of the lathe, slides along the bed of the machine to drill holes or act as a support point during machining.

The lathe tailstock

Before looking at the lathe centre it is essential to know the parts of the body of the tailstock of this machine tool:

• Tailstock spindle: a moving element, cylindrical on the outside but tapered on the inside with a coupling, generally of the Morse type. Thanks to this tapered design, accessories housed in this part of the spindle can be fitted easily and quickly. These accessories are none other than the lathe centres (this includes the live centre) and the drill chuck. At the opposite end of the spindle is the nut that makes it advance or retract.
• Tailstock screw: a fixed element whose main function is to make the spindle advance or retract.
• Anchor: the part that holds the tailstock firmly to the bed or structure of the lathe.
• Sliding base: located at the bottom of the tailstock and in contact with the bed of the machine. This base, as its name suggests, can slide transversely to the axis of the lathe; this movement makes it possible to offset the tailstock for machining tapered workpieces.

Types of lathe centre

Lathe centres usually have a standard size that matches the tapered part fitted in the tailstock spindle of the lathe. This standard size is given what is called the Morse number and runs from Morse taper 1 up to number 7. The former refers to a very small lathe centre, while the latter is a taper of large dimensions.

Lathe centres are only used in certain operations and situations. For example, when, during straight turning, the shaft projects three times its diameter from the chuck of the machine; this avoids vibration of the workpiece shaft. These centres must also be used when the shaft projects twelve times its diameter. In addition, to use lathe centres you need to use centre drills, which prevent the lathe centres from being damaged.

Now, there are two types of centre on a lathe:

Dead centre

This in turn is subdivided into steel dead centres and tungsten carbide dead centres: the first is made of alloy steel and has a 60º angle at one end, while the Morse taper sits at the other; the one made of tungsten carbide has a steel body, but its tip has a part made of tungsten carbide, ground to 60º.

Live centre

The live centre is distinguished by a section with ball, tapered and axial bearings in which a shaft is housed, with a tip with a 60º angle at its end; this tip is made of alloy steel, hardened and ground to extend the service life of this part. At the other end of the live centre is the Morse taper body.