Taper shank drills, of which the shank is sufficiently large, are directly fitted in the tapered hole of the spindle nose. The taper shank tools of which the shank is too small to fit the taper hole of the spindle are held in a socket. 

The shank of this socket has a standard taper to fit in to the taper hole of the spindle. Still the smaller taper shank drills or other tools are first fitted with a sleeve, which fits in to the socket and the complete assembly in the spindle. 

The socket as well as sleeve both carries a key slot each and a tang is provided at the end of the tapered hole and helps in providing a positive drive for the tool as the grip of taper alone is not sufficient. 

The drift helps in taking out the socket, sleeve or the tool by driving it in to the key slot. By doing so the drift presses against the top of the tang and because of the taper on the shank as well as the corresponding hole, the part or the tool is driven out. Straight shank drills are always held in a drill chuck.

Holding Parallel Shank Drills

Holding Parallel Shank Drills

A drill chuck is the most useful device for holding the parallel shank drills and other small tools. Two types of chucks are commonly used.

1. Self centering three-jaw Chuck.

2. Quick change Chuck.

Self centering three-jaw Chuck

A drill chuck is capable of holding wide range of drill sizes and it is usually provided with radial fingers for this purpose. 

The chuck key is used for rotating the tool head body of the chuck. Inside the body, there are three radial fingers which carry teeth on their outer faces. These teeth mesh with three toothed blocks, mounted on ball bearings inside. For operating the chuck, the pilot of the key is inserted in the pilot hole so that the teeth of the gear, provided on the key, engage with the teeth provided on the body. As the key is rotated, the outer body rotates together with the toothed blocks inside. 

This forces the fingers to move out wards or in wards, depending on the direction of rotation of the key. This enables a firm gripping of the tool or its loosening respectively. While operating this chuck, the drill spindle has to be stopped and then only the key is fitted and rotated.

Quick change Chuck: 

It is mainly used in mass production work. The main advantage of this chuck is that the machine spindle is not required to be stopped, while changing the tool. 

Thus a number of tools can be held and replaced quickly, one after the other, without stopping the spindle. This type of requirement is always there, when a number of different operations like reaming, boring, spot facing etc are to be performed repeatedly on the same machine, such that a different tool is to be held for each operation.

A drill chuck is normally permanently fitted to the drill spindle on smaller and lighter type of drill machines. But on larger and heavier type of machines, the chucks carry standard taper shanks, which fit in to the corresponding tapered holes in the spindles.

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