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What is Hobbing USE?
- Jan 24, 2018 -

What is Hobbing USE?

Hobbing is used to make the following types of finished gears:

  • Cycloid gears (see below)

  • Helical gears

  • Involute gears

  • Ratchets

  • Splines

  • Sprockets

  • Spur gears

  • Worm gears

Hobbing is used to produce most throated worm wheels, but certain tooth profiles cannot be hobbed. If any portion of the hob profile is perpendicular to the axis then it will have no cutting clearance generated by the usual backing off process, and it will not cut well.

Cycloidal forms

For cycloidal gears (as used in BS978-2 Specification for fine pitch gears) and cycloidal-type gears each module, ratio and number of teeth in the pinion requires a different hobbing cutter, so the technique is only suitable for large volume production.

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. A variant on this is still included in BS978-2a (Gears for instruments and clockwork mechanisms. Cycloidal type gears. Double circular arc type gears).

Tolerances of concentricity of the hob limit the lower modules which can be cut practically by hobbing to about 0.5 module.

History

Many manufacturing firms that maintain museums of how products were produced in times past will have examples of manual gear hobs that helped to produce gears prior to the gears of the 19th century and earlier. Along with these completely manual gear hobs will be samples of some of the first semi-automated gear hobs, and finally examples of more recent technology that demonstrates the fully automated process that modern gear hobs use to produce gears today. A few producers of gear hobs also have interesting literature on the history of gear hobs, including details about how modern gear hobs can produce thousands of gears in a single hour.