Bore gauge

A bore gauge is a collective term for the tools that are unique to the process of accurately measuring holes.

They are a direct equivalent of inside calipers and require the operator to develop the correct feel to obtain repeatable results.

The full-ball gauges are easier to set correctly and maintain, under the pressure of measurement, a better representation of the bore.

Half-ball gauges tend to spring just a little bit, and this may be enough to make a measurement incorrect.

It should be lightweight, have low coefficient of thermal expansion, high modulus and stiffness (for example: carbon fibre or aluminium).

This method is not the most accurate because there can be high human error and variation in the micrometer is passed down into the dial bore gauge.

When using a micrometer to set a dial bore gauge, the accuracy of the measurement will be 0.002 inches or 0.0508 millimeters.

The needle is moved when measuring the bore and mechanically or electronically transfers that data to the dial or readout.

The head also includes an interchangeable end that is used to set the nominal size, and reference contacts to aid in alignment with the bore.

Once inserted in the bore, the gauge can be slightly tilted back and forth to produce measurements.

The smallest measurement that is displayed on the dial represents when the head is perpendicular to the bore.

This will be the accurate measurement in reference to the nominal value that the dial bore gauge was zeroed at.