How to Read Dial Calipers

To properly build an engine, dial calipers are necessary in order to measure the distance between two points with precision. The distance between two points is critical to ensure that proper tolerances are achieved. Distances which are too wide or too narrow will lead to mechanical failure.

Instructions

1. Identify the different components of the dial calipers. Position the dial calipers so that the dial faces you. The dial is the circular piece with a needle inside. Note that on the bottom of the dial is a small screw. This screw is used to calibrate the caliper dial. The jaws underneath the dial are called the lower jaws, while the jaws above the dial are referred to as the upper jaws. Also note the numbers which run along the length of the calipers. These numbers are called the scale. Underneath the scale and to the right of the dial is a thumb screw that is used to open and close the calipers.

2. Calibrate the scale to read "0" when the calipers are closed. To close the calipers, turn the thumb screw in a clockwise direction until the calipers are closed. Loosen the small screw on the bottom of the dial by turning the screw in a counterclockwise direction. The face of the dial can now be turned. Turn the dial until the needle points to "0," then lock the dial into place by turning the small screw at the base of the dial clockwise.

3. Measure the diameter of an object with the calipers. Open the calipers by turning the thumb screw in a counterclockwise direction. Fit the caliper's lower jaws around the object to be measured. Look at the scale along the length of the calipers and count the number of inches indicated. The scale works the same way as a ruler. Therefore, if the scale reads "3," the distance is at least three inches. There are ten points between each inch on the scale. If the scale reads 3.5, the measurement is 3 ½ inches. Read the precise measurement by then looking to the dial. The dial reads from 0 -- 99. Each number on the dial denotes .001 of an inch. Therefore, if the scale reads 3.5, and the dial's needle rests on 10, the precise diameter of the object is 3.510 inches.

4. Measure the distance between two points. Whereas the lower jaws measure the diameter of an object, the upper jaws measure the distance between two objects. Open the calipers by turning the thumb screw in a counterclockwise direction until the upper jaws rest against the two objects. Read the distance between the two objects in the same manner used to measure the diameter of an object in step 3.