To Measure the Diameter of a Recessed Hole (Metrology)

It is impossible to measure the diameter of a recessed hole by micrometer or any of the conventional instruments. A lot of difficulty is,generally experienced in measuring the diameters of the recessed hole. A simple method of measuring the diameter by two balls of different diameters is given below.
The two balls are placed upon each other as shown in Fig. 9.18, i.e. balls must be touching each other and also the sides of the walls. With the help of a depth micrometer the distance from top surface, to the top surface of both the balls is measured. Let these distances be hx and
h2 and the diameter of the balls di and d2 respectively. 0\ and 02 are the centres of the two balls.
tmp3C66_thumbFig. 9.18
Fig. 9.18

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