What Is a Helix Angle?

The acute angle between the tangent of the cylindrical spiral line on the cylindrical surface and the straight generatrix of the cylindrical surface passing through the tangent point is called the spiral angle.

On a cylindrical surface,

Helical gears, worm gears, and other parts are generally used to indicate the inclination of the gear teeth. The helix angle of the worm is very large, and it is customarily expressed by the lead angle. Gear helix angle types are as follows:

1. Pitch circle helix angle : the angle formed between the tooth tooth length curve and the axis on the pitch cylinder. The helix angle of the helical rack is the intersection angle between the axial plane and the tangent plane on the pitch plane. Unless otherwise specified, helix angle refers to the helix angle on the pitch cylinder.

2. Base circle helix angle _{b: The} base circle helix angle refers to the helix angle on the base cylinder.

3. Axial base circle helix angle _{x b} : The axial base circle helix angle refers to the angle formed between the tangent plane and the axial plane on the axially acting plane. ^[1]

To process gears with different helix angles on a gear shaper, it is necessary to replace the spiral guides with different helix angles, and also to make gear cutters with different helix angles. Here, it is very troublesome to replace a set of spiral guides, and it is not easy to manufacture-harrow helical gear cutters. If we specify a spiral guide, the method of changing the number of teeth of the inserting cutter according to the standard modulus is adapted to a certain range of different spiral angles. In other words, when we design the internal and external gear parameters, if the helix angle specified by the spiral guide can be selected according to the magnitude of the modulus, then using the same spiral guide, as long as the gear shaper is replaced, it can be processed Range of internal gears with different helix angles. In this way, the auxiliary time for replacing the spiral guide rail is greatly shortened, and the processing economy is very prominent. ^[1]

There are many ways to measure the helix angle. It is best to have an existing helix angle measuring instrument. Otherwise, the following methods can be used:

Roll printing

Coat the top of the gear with a thin layer of red oil, and make its end face a ruler, and roll on white paper. At this time, a tooth print is left on the paper strip, and the helix angle of the tooth print is obtained by using a protractor. The helix angle measured by this method is the helix angle of the tooth tip circle, the helix angle _f on the index circle, and then solved according to the corresponding formula. The helix angle obtained by this method is approximate, because has errors. This method basically meets the requirements when mapping helical gears replaced in pairs. However, when only one gear is changed, this measurement method cannot meet the requirements. In particular, helical cylindrical gears with variable displacement are not suitable for measuring the helix angle with this method. Because the helical angle of the helical cylindrical gear and the displacement coefficient compensate each other, that is, the measurement error of the spiral angle will affect the value of the displacement coefficient.

In order to make the correct fitting without affecting the original design performance, a measurement method with high numerical accuracy must be used. Commonly used methods are "universal milling machine method", "ball method", "method of measuring tooth pitch" and so on. ^[2]