What Is an Inside Micrometer?
An inside micrometer is a precision measuring instrument designed to measure the inside diameter of hole shapes. It typically features three variations: a three-point measuring instrument for inside diameter, a dial gauge type measuring the extent of element push-in, and a rod-shaped version for measuring larger diameters. Some instrument manufacturers may use the term “Inside Micrometer” exclusively for the rod-shaped type that measures by two-point contact.
Uses of Inside Micrometer
Inside micrometers are primarily used in the manufacturing, quality control, and product development of industrial metal products. They are crucial for measuring not just circular inside diameters but also groove widths and distances. However, due to their structural limitations, they are not suitable for measuring very small diameters or dimensions, where alternative instruments like pin gauges or image measurement systems are recommended.
Principle of Inside Micrometer
The inside micrometer operates by making direct contact with the inside diameter of a hole and reading the distance between the measuring elements. The measurement is typically read from a micrometer or a dial gauge. Rod-shaped inside micrometers measure the inside diameter based on the screw’s forward or backward movement. They lack a ratchet, thus requiring careful application of measuring pressure. The 3-point inside micrometer uses a conical transducer to convert screw movement into the opening and closing of the measuring element, typically equipped with a ratchet for consistent measuring pressure.
Types of Inside Micrometers
1. Hole Test ABS Borematic
This type of inside micrometer measures by inserting the measuring element into the bore and reading the micrometer attached to the spindle. Three-point measuring instruments are known for stable measurements but have a limited measuring range.
2. Inner Micrometer
The rod-shaped inside micrometer measures the inside diameter by contacting the bore with both ends of the instrument. Accurate measurement requires careful positioning and practice.
3. Cylinder Gauge
Cylinder gauges are two-point contact instruments with readings provided by a dial gauge or a digital display. They allow for constant measuring pressure but require attention to the tilt between contact points.
Note that some inside micrometers may also refer to air micrometers and electric micrometers, which measure non-contactually by detecting the gap between the probe and the hole using air or electrical means.