Another form of chuck centre or driving centre for wood work is shown in [Fig. 772], being especially useful when the work cannot be supported by the lathe dead centre. The body a screws on to the thread on the live spindle of the lathe, while the work screws on the pointed screw b, which will hold disc-shaped pieces of moderate diameter, as about 4 or 5 inches, leaving its face to be operated on as may be desired. To prevent b from splitting the work, or when hard wood is to be turned, a small hole may be bored up the work to permit b to enter sufficiently easily.
When a piece of work to be turned between the lathe centres is of such a form that there is no place to receive centres, provision must be made to supply the deficiency.
Fig. 773.
In [Fig. 773], for example, a temporary centre b is fitted into the socket to receive the centre.
In small work that has been drilled or bored, a short mandrel is used instead of the piece b.
Fig. 774.