instructions for mechanical all-purpose OD micrometers
Zero-setting Mitutoyo micrometers (mechanical/analog)
There is no easier way to make measuring errors with serious consequences than to use a micrometer that has not been set to zero. Before use, even with a brand new micrometer, be sure that it is set to zero. The manufacturer admonishes us to "observe the following points to correctly zero adjust the micrometer." .
- Rotate the ratchet stop 1-1/2 to 2 times to exert a constant measuring force.
- Allow sufficient time for the micrometer [to become] thermally stabilized, especially when moved from a significantly different temperature.
- Zero adjust the micrometer in a posture in which measurements are actually performed.
- Use a calibrated standard bar (micrometer standard).
With the spindle closed on the 0-1" micrometer, or closed onto a micrometer standard for larger micrometers, the zero of the barrel should coincide with the zero on the rotating thimble. For instance, on a 1-2" micrometer you must insert a 1" standard and close the thimble. If the zeros don't line up, use the wrench which came with your tool, hook it around the barrel so it fits into the small hole and gently turn the barrel until the zeros line up. If the barrel won't budge, use the back of a screwdriver to gently tap the wrench. Old micrometers may have become corroded and the barrel won't move. In this case you'll have to send it in for reconditioning. Micrometer wrenches are available if you've lost yours.
It follows that zero-setting a 2-3" micrometer requires a 2" micrometer standard (measuring rod), a 3-4" will require a 3" measuring rod, and so forth. Further information on measuring rods can be found on page 58.