Worm Gage

a gear-measuring instrument designed to measure the deviation of the actual helix of a helical spur gear tooth from the calculated helix. The operation of a worm gage is based on the principle of reproducing the calculated helix by a mechanism of the gage and comparing the calculated helix with the actual helix, which is obtained as a trace of the cross section of the tooth surface on a cylindrical surface that is coaxial with the gear shaft. A worm gage makes it possible to detect both the total deviation of the helix angle from the calculated angle and local errors. Existing worm gages are designed for the inspection of gears with a diameter of up to 400 mm.

Worm gages are classified according to the method used to reproduce the calculated helix. In the simplest worm gages, the helix is reproduced by means of a template that has a helix with the same parameters as the helix of the gear being inspected. Such a worm gage is used to inspect gears during mass production. In other worm gages, the helix is reproduced by a mechanical device—for example, a sine bar or a lever device—that simultaneously rotates the gear being inspected and shifts a probe tip containing a primary transducer. In some gages of this type, the mechanical device simultaneously rotates and shifts the gear being inspected with respect to a fixed probe tip that contains a primary transducer. Worm gages that employ a computer rather than a mechanical method of comparing the actual and calculated helices of a gear are widely used.