A dial indicator is a device used for measuring very small increments. It is used in the machining process for quantifying precision metal parts. There are generally three types of incremental measurements used by the dial indicator. The largest increment is .005, pronounced five-thousandth of an inch. The next smallest is .001, pronounced one-thousandth of an inch. The most accurate measurement is .0001, called one ten-thousandth of an inch. Reading a dial indicator is only a matter of understanding the two dials on the large gauge. A small dial, located on the lower portion of the large faced gauge, indicates one revolution of the large dial in .100 movement. The large pointer is broken down into the indicators small measurements. The indicators precision measurement specification is always shown on the face of the gauge. For the example below, the indicator push arm has a full movement of one inch and is broken into .001" increments.
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- One-inch dial indicator .001" increments
Note the large dial face on the indicator. The large dial has numbers graduated by 10. It is listed 0 through 90. Between each number, there are 9 small lines that indicate a measurement of .001".
Observe the smaller dial below the large hand of the .001" movement. It has numbers on the face, and they are also broken into 10 separate numbers. The range is .0 to .9, where .9 is equal to .900" or nine-hundreds of an inch. One inch on this dial indicator is equal to the reading 1.000".
Adjust the indicator to zero by loosening the outer indicator ring. A small thumbscrew can be loosened and tightened to adjust the .001" measurement ring. By moving the zero ring, you can calibrate the indicator for any position.
Push on the indicators push arm. Set the dials to the following position. The small dial is on .4". The large dial is at 10. The inch reading would be .410".
Relieve some pressure on the movement arm. Have the large dial come down to five lines below the 10. The reading in inches is now .405".
Allow the dial indicator to come back to a full zero by letting go of the push arm. Double check the outer ring to register that the 0 is behind the large dial on the indicator face.
Move the indicator to the following position. Place the small dial on .1 and the large dial on five lines past the number 20. The reading in inches is .125" or 1/8 of an inch.
Depress the rod even further until the small dial is at .2 and the larger dial is at 50. The reading is now .250" or ¼ inch.
Push the rod a little further until the small dial is on .5 and the large dial is on 0. This indicates that the push arm has now moved .500" or a ½ inch.
You can practice some more by moving the arm to the following positions. Small dial on .3 and the large dial 5 lines past 70 is equal .375" or 3/8 inch. Small dial on .6 and the large dial 5 lines past 20 is equal to .625" or 5/8 inch. Small dial on .7 and the large dial on 50 is equal to .750" of ¾ inch.
Tips and warnings
- Keep all dial indicators in a dry location. Moisture can ruin the precision movement.
- When moving a dial indicator from a cold area to a warm area, always allow the dial indicator to acclimate to the surrounding temperature.
- Never allow the indicator to become wet or covered in oil. Both of these situations will damage the internal mechanisms.