Hobbing

Hobbing is relatively fast and inexpensive compared to most other gear-forming processes and is used for a broad range of parts and quantities.

[4][self-published source] It was a simple design, but the rudimentary components are all present in the customary patent drawings.

The hob cutting tool and the gear train to provide the appropriate spindle speed ratio are clearly visible.

[7] For very large gears, the blank may be preliminarily gashed to a rough shape to make hobbing more efficient.

The necessary addendum correction to allow the use of small-numbered pinions can either be obtained by suitable modification of this rack to a cycloidal form at the tips, or by hobbing at a diameter other than the theoretical pitch.

For example, a 10 in (250 mm) capacity machine can generate gears with a 10 in pitch diameter and usually a maximum of a 10 in face width.

These teeth have grooves that run the length of the hob, which aid in cutting and chip removal.

There are slight changes to the shape for generating purposes, such as extending the hob's tooth length to create a clearance in the gear's roots.

Modified tooth profiles are usually used to add strength and reduce size and gear noise.

To circumvent this problem, a special war-time emergency circular arc gear standard was produced giving a series of close-to-cycloidal forms which could be cut with a single hob for each module for eight teeth and upwards to economize on cutter manufacturing resources.