Cutting of Helical Gears

Cutting of Helical Gears

Cutting of Helical Gears - The following methods are used for cutting helical gears.

(a) Milling

(b) Hobbing

(c) Shaping

(d) Rack cutting

Milling is used less than any other method, because of the difficulty in obtaining high accuracy and productivity,

Hobbing is used extensively for generating the teeth of helical gears for any production volume. In medium to high production, it is common to use fixtures that allow hobbing of two or more identical gears in one loading of the machine.

When hobbing spur, gears with a single thread hob, the blank rotates one tooth space for each rotation of the hob, the rotation being synchronized by means of change gears, When hobbing helical gears, the rotation of the work is retarded or advanced in relation to the rotation of the hob, and the feed is also held in definite relation to the work and the hob.

Whether the workpiece rotation is retarded or advanced depends mainly on whether the hob is a single thread or multiple thread type, The amount by which the workpiece is retarded or advanced depends on the helix angle