Involute-Profile-Measuring Instrument

an instrument designed to measure the contours of involute gear teeth in a section perpendicular to the axis of the gear wheel. It functions by comparing an involute generated by the instrument with the actual involute of the tooth profile. Depending on the design of the mechanism for generating the involute, such gauges are classified as individual (disk) and universal types. In a disk-type instrument, the comparison curves are reproduced by means of interchangeable disks having diameters equal to those of the base circles of the gear wheels being checked. In universal instruments the curves are reproduced by a special device that is adjusted for the different radii of the base circles. Among the most popular of the latter type are instruments in which the generating mechanism contains a disk of fixed diameter and a lever-band linkage or a mechanism having a fixed involute template and a lever linkage. The disk-type instruments are the most accurate.

Involute-profile-measuring instruments are made in several standard sizes for measuring tooth contours of both internal and external gear wheels having base circle diameters usually between 40 and 1,250 mm. They are usually provided with an auxiliary device for measuring the helix of helical gear wheels (seeWORM GAGE) that moves the measuring point of the indicating mechanism along the axis of the gear wheel being measured as the wheel turns. Measurements are usually obtained by means of a recorder.

A promising advance in the development of involute-profile-measuring instruments is a system that uses pulses from a transducer and a miniature computer. In a number of such instruments the gear wheel being measured is rotated and the measuring point is shifted so that pulses that are proportional to the angle of rotation of the gear wheel and to the linear movement of the point arrive simultaneously at the computer. The data are compared in the computer with theoretical values previously supplied. In other versions the theoretical angles and the linear movements of the gear wheel and measuring point are provided by the computer, and the indicating device gives the deviation of the actual contour from the theoretical values.