What Is a Jaw-Type Micrometer?
A jaw-type micrometer is one of the special micrometers used to measure the tooth thickness of spur and helical gears.
It is characterized by the special shape of both measuring elements of the micrometer, which are suitable for measuring gears. It is used to measure straddle tooth thickness, which is measured by placing multiple teeth between them.
Depending on the type, there are two types: an analog type that displays dimensions on a scale, and a digital type that displays numerical values digitally and uses a ratchet stop to measure with constant pressure.
Uses of Jaw-Type Micrometers
Micrometers are mainly used to measure the straddle tooth thickness of spur and helical gears.
Another measurement method used for the same purpose is called the over-pin method, which uses a ball gear micrometer with a precision-machined steel ball as the measuring element, and measures by inserting the steel ball into the grooves of the relative teeth.
The jaw-type micrometer’s measuring element is long, thin, and delicate. Therefore, it must be handled with care when measuring.
Features of the Jaw-Type Micrometers
Measurement of straddle tooth thickness using a jaw-type micrometer is subject to errors in the measurement results due to differences in the contact conditions of the measuring element and the pressure angle between the left and right sides.
Nevertheless, it is the most commonly used method for measuring tooth thickness because the measured value can be converted to the tool drive of the machine tool. Therefore, it is the most common method used to measure tooth thickness.
On the other hand, the over-pin method measures by applying a steel ball to the gear, so errors due to the degree of contact are unlikely to occur. However, in order to measure properly, it is necessary to prepare a steel ball with a diameter that matches the gear size and pitch. In addition, there is the time-consuming task of calculating the appropriate diameter.
In the case of even-numbered teeth, the measurement is made by placing the pin in the groove of the relative tooth, while in the case of odd-numbered teeth, the measurement is made by placing the pin in the groove 180/z(°) offset from the tooth.
The internal diameter measurement of internal gears is also known as the Vitrine pin method.