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A Guide to Double Helical and Herringbone Gears

September 19, 2019

A Guide to Double Helical and Herringbone Gears

The delivery of power and motion between two shafts in rotation is carried out through a gear and its teeth.


The gears we will be focusing on in today’s piece are helical gears and their permutations, namely Double Helical and Herringbone gears.


What Is the Difference Between Double Helical and Herringbone Gears?

A double helical gear can be identified if the pair of helical gears demonstrate opposite helix cuts on a gear blank with a narrow gap, allowing them to maintain the benefits of helical gears while also ensuring axial thrust loads are negated.  


The subtle difference between a double helical gear and a herringbone gear can be seen if the two gears have no groove between them, meaning they interact at a common point. This allows for the operation of these gears at high speed without producing noise. This difference means a dedicated machining process is required for their fabrication.  


Machining Herringbone Gears

An effective cutting process for a herringbone gear typically involves hobbing, milling, and shaping, though these methods depend largely on whether or not a gap is required between the two helixes or if the herringbone is to be continuous.


1) Hobbing

When cutting herringbone teeth, rotary cutters and hobs are typically used. However, their functionality is only effective when there is a gap large enough to allow for cutter runout between the right and left helixes. Hobbing machines can be manufactured today to machine herringbone teeth in gears up to 5.6m in diameter.


2) End Milling

Cutting teeth in herringbone gears is not solely regulated to hobbing machines; end mills also have the capability of machining teeth, unaffected by whether or not the gears possess centre slots. Herringbone gears with a large diameter are generally better suited to be cut by end milling.


3) Shaping

Finally, we come to shaping – another suitable method to cut teeth on herringbone gears, provided they are continuous and contain a centre slot. Many similarities exist between the shaper used for cutting a helical gear and a herringbone gear, however, in the case of the herringbone gear two cutters – one for each helix -are controlled at once by an operator.


We have been fabricating top-class helical gears for over 40 years at True Gear and Spline Ltd. Our recent transition to a 22,000 sq ft. facility has given us the means to house the latest in machining technology, ensuring your gears and splines are made with precision in mind. Reach out to us to see how we can meet your gearing needs!