CALIPERS

Dial calipers are precision measuring instruments that are used to check the thickness, inside or outside measurements of parts. Some calipers have a rod that extends out of the end that is used to measure depth and steps.

These calipers have an easy to read dial with a needle that moves like an analog clock, and indicates the measurements as the caliper is opened and closed. A gear behind the dial drives the needle in the dial as the gear moves across teeth on a rack in the body of the caliper.

Some racks are on top, others are on the bottom. Some are covered, others have all the teeth exposed. Care must be taken to keep the rack clean and clear of dirt and debris. A clogged tooth on the rack may prevent the dial caliper from opening or closing. If clogged, and the caliper is forced open or closed, you will get an incorrect reading as the gear jumps over the clogged tooth in the rack.

The easiest dial caliper to read and use has .100” of measurement per revolution. Dial calipers are generally available with inch or millimeter readings. Some have fractions, used by those in the jewelry making and watch making trades.

Measuring with a dial caliper requires a combination of reading the graduations and numbers on a linear scale along with the graduations and numbers in the dial. Each line, or graduation, on the linear scale indicates .100”, a number 1 indicates 1”, number 2 indicates 2”, etc.

The dial usually indicates either .100” or .200” of travel per revolution of the needle. Each line on the face of the dial equals .001”, there are 10 groups of 10 lines per group, for a total of 100 lines on a dial with .100” per revolution, 200 lines with .200” per revolution.

Begin by cleaning the caliper jaws. Simply close the jaws on a clean piece of paper, and slide the paper out. This will remove any light dirt, grease, oil, etc. With the jaws in the closed position, adjust the dial to the zero position. You are now ready to measure your parts.

Carefully open the caliper, noting the position of the moving edge of the caliper relative to the lines on the linear scale. For example, if the edge is on the ninth line you are at .900”. Then note the position of the needle on the face of the dial. If the needle is pointing between the 0 and the 10, on the 7th line, this is .007”.

Add the .900” to the .007” and the reading on your dial caliper is .907”.

Dial calipers are made in many different countries, of many different materials, and are of many different qualities. Not all calipers are alike. Like anything else, you get what you pay for.