KEYS

A machine derives the energy or power for its working from a prime mover. The power in the form of rotary motion is transmitted from the prime mover to the machine either by connecting the prime mover shaft directly to the machine shaft by a coupling or using intermediate machine elements such as gears or pulleys and belts or sprockets and chains. in all these cases the shaft is secured firmly to the flanges or gears or pulleys or sprockets which are mounted on it to prevent the relative rotation between the two a tight fit of the shaft in the bore will be usually insufficient to secure the shaft to the machine element which is mounted on it.

Types of keys:

Keys are classified into two main types (1) taper keys (2) parallel or feather keys. A tapered key is of rectangular or square section with uniform width and tapering thickness. It transmits the turning moment between the shaft and the part mounted on it without any rotational and axial motion between them a parallel key is of rectangular or square section with uniform width and thickness throughout it transmits the turning moment between the shaft and the part mounted on it and also permits the axial motion between them.

The different types of taper keys are:

·      Taper sunk key

·      Saddle key

·      Flat key

·      Gib-head key

The different types of parallel keys are:

·      Parallel or feather sunk key

·      Peg key

·      Single headed feather key

·      Double headed feather key

·      Spline shaft

 Taper sunk key:

Taper sunk keys are of rectangular or square section uniform width with their bottom surface straight and upper surface tapered. The ends of the keys may be squared or rounded either on one or both the ends as since the bottom surface of the key is straight the key way in the shaft will be parallel to its axis. Generally the depth of the key way in the shaft is one half of the thickness of the key when measured at the side of the key way and not when measure on the centre line. However for the keys recommended by the Indian standard institution the depth of the key way in the shaft t measured on the center line of the shaft may be obtained from since the upper surface of the key is tapered the keys way in the part to be mounted on the shaft is also tapered.

If D is the diameter of the shaft in mm

Width of the key  W =0.25D +2 mm

Thickness of the key      T = 0.66 W

At the thick end

Standard taper               l: 100

TAPER KEY 12 X 8 X 50

Saddle key:

A saddle key is of uniform width but tapering in thickness on the upper side and the underside is hollow to fit the shaft since the saddle key holds the shaft and the part mounted on it by friction only it is not suitable for heavy loads this key is used when there is frequent alteration in the position of the key on the shaft the approximate empirical proportions of a key are.

If D is the diameter of the shaft in mm

Width of the key  W =0.25D +2 mm

Thickness of the key      T = 0.35 W

At the thick end

Standard taper               l: 100

SADDLE KEY         12 X 4 X 50

Flat Saddle key:

A flat saddle key is of rectangular section width with the bottom surface straight and the upper surface tapered the flat saddle key is fitted partly into the part to be mounted on the shaft and rests on the flat surface formed on the shaft the flat saddle key holds the shaft and he part mounted on it by the wedge action when the shaft rotates the key is wedged between the flat surface of the shaft and key way of the part mounted on the shaft this type of key is used only where comparatively light work and also less expensive them the sunk keys because of the absence of the key way in the shaft the approximate empirical proportion of a flat saddle key.

If D is the diameter of the shaft in mm

Width of the key  W =0.25D +2 mm

Thickness of the key      T = 0.5 W

At the thick end

Standard taper               l: 100

FLAT SADDLE KEY         12 X 6 X 50

Gib head key:

When a tapered sunk key is used it can be removed by driving out from the exposed small end if this is not accessible a head called Gib is provided integral with the tapered sunk key at its thicker end when a Gib-head key is to be removed a wedge is forced into the gab between the head of the key and end face of the part mounted on the shaft the key ways should be cut in both shaft and the part mounted on it as specified in the case of tapper sunk key the edge of the key may be chamfered to 45 the inside edge the key way also be rounded the approximate empirical proportion of the Gib-head key.

If D is the diameter of the shaft in mm

Width of the key  W =0.25D +2 mm

Thickness of the key      T = 0.66 W

At the thick end

Standard taper               l: 100

Height of the        h = 1.75 T

Width of the head b = 1.5 T

GIB-HEAD KEY      12 X 8 X 50