What Is an Indicating Micrometer?
An indicating micrometer is a type of external micrometer, with an indicator built into the anvil side, sometimes called a snap meter.
The body has a pushbutton to allow the anvil to be moved back and forth. This mechanism makes it easy to attach and detach the measuring object while the spindle is fixed. The amount of movement of the anvil is indicated on the indicator. With the center set at zero, the anvil moves with an approximate runout of 40 to 60 µm. When no measuring force is applied, the anvil swings out to the minus direction.
Uses of Indicating Micrometers
An indicating micrometer is used to measure many external dimensions of similar shapes. Since the anvil side can be moved to attach and detach the object to be measured easily, numerous parts can be measured efficiently. Since the spindle needs to be fixed during measurement, the parts must be of variable dimensional value within the tolerance range when using the anvil.
In addition, since the anvil swings out in the negative direction, the spindle is pushed in during measurement so that the needle is zeroed each time, thereby keeping the measuring pressure constant.
Principle of Indicating Micrometers
The parts of an indicating micrometer are divided into two main structures. The structure can be thought of as a combination of an outer micrometer, and a dial indicator. The spindle part has the same structure as the outer micrometer, and the scale reading is the same. The indicator section indicates the scale by replacing the amount of pushing in of the anvil with the rotation of the needle, and the needle moves with an amplitude of plus or minus 40 to 60 µm, with zero at the center.
When measuring, both the instrumental error of the main unit and the indication error of the indicator section must be taken into account. The repeatability of the indicator’s indication is also an error factor, so the degree to which measurement error affects the measurement results must be considered when applying the measuring instrument.
When in use, the anvil is pushed in slightly and the indicator and spindle scale are both set to zero as the base point. Some models have an adjustment mechanism for the zero position, so the base point of the indicator section can be shifted to match the variation of the measurement target.