It is a lathe accessory. It is used to support a lengthy work to carry out lathe operations. When a work is held in a chuck, the centre is assembled to the tailstock, and it supports the overhanging end of the work. The work is
to be provided with a centre drilled hole on the face of the overhanging end. When the job is held in between centres to carry out the operation, it functions together with a driving plate and a suitable lathe carrier.
The centre, which is accommodated in the main spindle sleeve, is known as a ‘live centre’ and the centre fixed in the tailstock spindle is known as a dead centre. In construction, both centres are identical, made as one
unit that consists of a conical point of 60° included angle, a body provided with a Morse taper shank and a tang. The dead centre is made out of high carbon steel, hardened and around whereas the live centre need not have its conical tip hardened as it revolves with the work. A good lubricant should be used for the dead centre.
Different types of Lathe Centres are as follows
- Ordinary centre
- Half centre
- Tipped centre
- Ball centre
- Pipe centre
- Revolving centre
- Insert-type centre
- Self-driving live centre
- Female centre
- Swivl “V” centre
1. Ordinary Centre
Ordinary Centre are used for general purpose.
2. Half Centre
Though it is termed as half centre, little less than half is relieved at the tip portion. Used while facing the job without disturbing the setting.
A carbide or a hard alloy tip is brazed into an ordinary steel shank. The hard tip is wear- resistant.
4. Ball centre
Minimum wear and strain. Particularly suitable for taper turning.
5. Pipe centre
Used for supporting pipes, shells and hollow end jobs.
6. Revolving centre
Revolving Centres are Frictionless. Used for supporting heavy jobs and jobs revolving with high speeds. A high-speed steel inserted centre is supported by two bearings housed in a body. It is also called the revolving dead centre.
7. Insert-type centre
Economical. Only the small high-speed steel insert is replaced.
8. Self-driving live centre
Self driving live centre is usually mounted on the head-stock spindle. Used while machining the entire length of the job in one setting. Grooves cut around the circumference of the centre point provide for good gripping of the job and for getting the drive. This centre can be used for only soft jobs and not for hardened jobs.
9. Female centre
Female centre is used to support the end of the job where no countersink hole is permitted.
10. Swivel “V” centre
Swivel “V” centre is used to support a job in the `V’ portion and to drill holes across the round job by using a drill bit in the headstock spindle.