Long and slender work pieces are turned between centres- Live centre with headstock spindle and dead centre at the tailstock spindle.
They are made out of very hard materials to resist wear and deflection. The included angle of the centre is usually 60 degree for general work and 75 degree for heavy work. The shank of the centre is machined to morse standard taper (0-6). Different types of centres are:
Ordinary centre
Ball centre
Revolving centre
Half centre
Tipped centre
Insert type centre
Pipe centre
Ordinary centre is a general purpose centre.
Ball centre is specially used while taper turning to support the end.
Revolving centre is a frictionless centre fitted with bearing which is suited for supporting jobs running at high speed.
Half centre is used while facing operation to clear the tool.
The centres tipped with hard alloys are excellent to resist wear but expensive.
Pipe centres are used to support the hollow parts.
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