20th May 2020, Period 7, Class 12, Engineering Graphics, Machine Parts - Keys - 1

Dear Students,

Good Morning and a warm welcome to today's class.

It feels really nice to meet up for yet another class this morning.

Recall that in our last class, we had learnt about the RIVETS.

Let us now proceed further and learn about another machine part called as KEYS.


What is a KEY?

A key is a piece of metal which is used to fasten two parts together. More specifically, a key is used to join or tighten two circular moving parts together. For example, moving parts such as pulleys and flywheels are joined to the shaft by means of a key. A key prevents relative motion between the two parts so that these can rotate as one composite part. The key can be unfastened and removed. Therefore it is a temporary fastener.

There is a groove cut out on the shaft as well as the pulley, within which a key is seated. The groove is called as the key way.

Types of Keys

1. Rectangular Sunk Key
2. Woodruf Key
3. Gib Head Taper Key
4. Double headed feather key


1. Rectangular Sunk Key

The rectangular sunk key has a rectangular cross section, and a taper that runs along its length. The typical taper is 1: 100. Refer to figure 1 below

What is Taper:  Gradual reduction in the thickness of the key as we move along its length is called as Taper. 


         
Fig 1: Rectangular Sunk Key

Supposing, the key is used on a shaft with diameter, d. Then:

1. Width of the key will be = d/4
2. Thickness of key, t = d/6
3. Length, L = 1.5 d
4. Taper = 1:100 

If the key is not provided with taper then the key will remain lose fitted in the key way and it will disengage when the shaft rotates at high angular velocity. 

Exercise

Q 1. Sketch free hand rectangular sunk key, in position, on a shaft of diameter, d = 40 mm keeping the axis of the shaft parallel to the VP and the HP.