How to Read a Depth Micrometer

Using A Depth Micrometer to Measure the Bore of a Hobby Engine

Accurately measuring the depth of a bore or channel is something that any engineer, mechanic or kitcar enthusiast needs to be able to do with a high degree of accuracy. A depth micrometer is the ideal tool for the precise measurement needed. Learning how to read a depth micrometer is easy. By understanding how to operate your depth micrometer you will be able to quickly set and read the gauge.

Things You'll Need

• Ruler (mm)
• Depth micrometer spindle
• Pen
• Paper
• Depth micrometer

Instructions

1. Measure the spindle for your depth micrometer. Your micrometer may have come with a set of spindle, select one and measure (in mm) the length of the spindle from the end to the beginning of the shank. The shank is where the spindle widens.

2. Insert the spindle shank into the bottom of the depth micrometer. The bottom of the micrometer is where the "scale" piece is attached, the scale extends out from the body of the micrometer looks like a handle on a sword. The spindle will fit into a small hole beneath the scale that has a locking knob extending from beneath the scale, turn the knob until you feel the spindle lock into place.

3. Hold the micrometer upright by grasping the grip above the thimble. The grip is the first cylinder of the micrometer which has a grip etched into its surface but no numbers. The thimble is a smooth shaft with a series of measured marks running horizontally around the bottom where the shaft of the thimble fits over the sleeve. The sleeve is the smooth shaft with numbers marked vertically on its surface.

4. Turn the ratchet knob that is centered in the very top of the micrometer above the grip. Depending on which way you turn the ratchet knob, the spindle will extend or retract.

5. Balance the sword handles of the scale on the top of the depression you wish to measure. Turn the ratchet knob until the spindle is extended to the bottom of the depression.

6. Write down the number on the sleeve that the bottom of the thimble is lined up with. Now add that measurement to the original measurement of the spindle. Add to that sum the measurement of 0.005mm (which is the industry standard width of the spindle locking knob). The result will be a precise measurement of the depth of your depression.

Tips & Warnings

• Before inserting the spindle, test a few spindles in the depression to see which one fits without the shank being below the upper edge of the depression.

• Always repeat your measurement three times, if the numbers are different, take the micrometer apart and reassemble and try again.

Resources

• Practical exercises for using a depth micrometer