The contact micrometer is an instrument that measures the dimensions of a particular by tightening it with a micrometric screw.
Generally, the term “contact micrometer” refers to external micrometers but there are also other types of micrometers, for example internal micrometers, depth micrometers or 3-point micrometers, depending on the different measurement applications.
The measurable range differs in steps of 25 mm - eg. from 0 to 25 mm and from 25 to 50 mm - depending on the size of the part to be measured, so it is generally necessary to use a micrometer that corresponds to the target.
To calibrate a micrometer, use a gauge block. In order to make accurate measurements, the anvil surface must always be flat. After several measurements, the surface may no longer be flat due to wear or dirt accumulation. Therefore, periodically use a part known as interferometric glass for flatness to check if the surface is flat according to the displayed Newton's rings.
When measuring a metal target and calibrating with a gauge block, pay attention to thermal expansion. Whenever possible, avoid holding metal with bare hands or use gloves that do not transmit heat and are designed for precision work.
The calibration interval of the micrometers is generally between 3 months and 1 year.