This is a disc of metal which screws onto the headstock spindle; it is drilled with a number of holes which enable a piece of timber to be screwed to it. When the turning is completed the base of the work has screw holes in it, or a large amount of timber has to be wasted to discard that part of the turning blank which housed the screws.
Another simple system is the screw chuck, suitable for small items. This is a woodscrew which is attached to the drive spindle; the timber is then screwed onto it.
There is now a tremendous variety of more sophisticated devices based on the engineering chuck. These are usually four jaw chucks which can grip a spigot or, with the same jaws, expand into a groove to grip the wood. These chucks have interchangeable jaws so they can be adapted for different types and sizes of turning.
Some chucks are designed to fit a specific size of headstock spindle, others are redesigned to take a range of inserts which allow the chuck to be used on different lathes - if you change lathes you don't need to buy a new chuck, just a new insert.
Early models of these chucks were operated by two tommy bars which meant that you needed three hands to load the timber, or use the tailstock to support the timber while it was being attached to the chuck. Most chucks are now operated by a single chuck key.
Most of the four jaw chucks are rather too large and heavy for use on the smaller lathes. There are several three jaw chucks suitable for the small lathes. These have their limitations: they are operated by two tommy bars and they have only one set of jaws - but they are not very expensive. Record and Charnwood have a small four jaw chucks with a single chuck key and four sets of jaws - not cheap but an excellent piece of equipment.
The size of timber that can be turned depends on the power of the motor and the distance between the drive spindle and the lathe bed. The distance from the spindle to the lathe bed clearly limits the size of timber that can be turned but it also affects the use of bowl gouges. To overcome these problems many lathes have a headstock which can be rotated so that the timber does not swing over the lathe bed. This may require an extra toolrest or the existing toolrest being moved to the other side of the headstock.