10/29/19Design of Machine Element and Cad Cam3IntroductionA key is a piece of mild steel inserted between the shaft and hub or boss of the pulley to connect these together in order to prevent relative motion between them. It is always inserted parallel to the axis of the shaft. Keys are used as temporary fastenings and are subjected to considerable crushing and shearing stresses. A keyway is a slot or recess in a shaft and hub of the pulley to accommodate a key.Types of KeysThe following types of keys are important from the subject point of view :1. Sunk keys, 2. Saddle keys, 3. Tangent keys, 4. Round keys, 5. Splines.1.Sunk Keys:The sunk keys are provided half in the keyway of the shaft and half in the keyway of the hub or boss of the pulley. The sunk keys are of the following types :1. Rectangular sunk key. A rectangular sunk key is shown in Fig. The usual proportions of this key are :Width of key, w = d / 4 ; and thickness of key, t = 2w / 3 = d / 6where d = Diameter of the shaft or diameter of the hole in the hub.The key has taper 1 in 100 on the top side only.Rectangular sunk key.
10/29/19Design of Machine Element and Cad Cam42. Square sunk key. The only difference between a rectangular sunk key and a square sunk key is that its width and thickness are equal, i.e. w = t = d / 43. Parallel sunk key. The parallel sunk keys may be of rectangular or square section uniform in width and thickness throughout. It may be noted that a parallel key is a taper less and is used where the pulley, gear or other mating piece is required to slide along the shaft.4. Gib-head key. It is a rectangular sunk key with a head at one end known as gib head. It is usually provided to facilitate the removal of key. A gib head key is shown in Fig(a) and its use in shown in Fig(b).