Herringbone

Herringbone (pronounced her-ing-bohn)

(1) A pattern, the weave resembling the skeleton of a herring fish, consisting of adjoining vertical rows of slanting lines, any two contiguous lines forming either a V or an inverted V, used in masonry, textiles, embroidery etc and .  Also called chevron, chevron weave, herringbone weave; a type of twill weave having this pattern.

(2) A fabric constructed with this weave.

(3) A garment made from such a fabric, applied especially to jackets and coats.

(4) In skiing, a method of going up a slope in which a skier sets the skis in a form resembling a V, and, placing weight on the inside edges, advances the skis by turns using the poles from behind for push and support.

(5) A type of cirrocumulus cloud.

1645–1655: The construct was herring + bone.  Herring was from the Middle English hering, from the Old English hǣring, from the Proto-West Germanic hāring (herring) of unknown origin but it may be related to the Proto-Germanic hērą (hair) due to the similarity of the fish’s fine bones to hair. It was cognate with the Scots hering & haring, the Saterland Frisian Hiering & Häiring, the West Frisian hjerring, the Dutch haring, the German and Low German Hereng & Hering, the French hareng, the Norman ĥéren and the Latin haringus; all borrowings from the Germanic.  Bone is from the Middle English bon, from the Old English bān (bone, tusk; bone of a limb), from the Proto-Germanic bainą (bone), from bainaz (straight), from the primitive Indo-European bheyhz (to hit, strike, beat).  It was cognate with the Scots bane, been, bean, bein & bain (bone), the North Frisian bien (bone), the West Frisian bien (bone), the Dutch been (bone; leg), the Low German Been & Bein (bone), the German Bein (leg), the German Gebein (bones), the Swedish ben (bone; leg), the Norwegian and Icelandic bein (bone), the Breton benañ (to cut, hew), the Latin perfinēs (break through, break into pieces, shatter) and the Avestan byente (they fight, hit). It was related also to the Old Norse beinn (straight, right, favorable, advantageous, convenient, friendly, fair, keen) (from which Middle English gained bain, bayne, bayn & beyn (direct, prompt), the Scots bein & bien (in good condition, pleasant, well-to-do, cozy, well-stocked, pleasant, keen), the Icelandic beinn (straight, direct, hospitable) and the Norwegian bein (straight, direct, easy to deal with).  The use to describe a type of cirrocumulus cloud dates from 1903.  The alternative form is herring-bone (not herring bone which would be a bone of a herring).

The herringbone shape (left) and a herring's bones (right).

The herringbone pattern picked up its rather fanciful name because of a resemblance to the fine bones of the fish.  First used in masonry, the motif has for centuries been used in wallpaper, mosaics, upholstery, fabrics, clothing and jewellery.  In engineering, the pattern is found also in the shape cut for some gears but this functionally deterministic.

Roman herringbone brickwork, Villa Rustica, Mehring, Trier-Saarburg, Rhineland, Germany.

The original herringbone design was a type of masonry construction (called opus spicatum, literally "spiked work”) used first in Ancient Rome, widely adopting during medieval times and especially associated with Gothic Revival architecture; it’s commonly seen today.  It’s defined by bricks, tiles or cut stone laid in a herringbone pattern and is a happy coincidence of style and structural integrity.  Although most associated with decorative use, in many cases the layout was an engineering necessity because if tiles or bricks are laid in straight lines, the structure is inherently weak whereas if built using oblique angles, under compression, loads are more evenly distributed.  One of the reasons so much has survived from antiquity is the longevity of the famously sticky Roman concrete, the durability thought in part due to chemical reactions with an unusual Roman ingredient: volcanic ash.

Lindsay Lohan in herringbone flat-cap.

Of gears

Although the term “herringbone cut gears” is more poetic, to engineers they’re known as double helical gears.  In both their manufacturing and operation they do present challenges, the tooling needed in their production demanding unusually fine tolerances and in use a higher degree of alignment must be guaranteed during installation.  Additionally, depending on use, there is sometimes the need periodically to make adjustments for backlash (although in certain applications they can be designed to have to have minimal backlash).  However, because of the advantages the herringbone structure offers over straight cut, spur or helical gears, the drawbacks can be considered an acceptable trade-off, the principle benefits being:

(1) Smoothness of operation and inherently lower vibration:  The herringbone shape inherently balances the load on the teeth, reducing vibration and generated noise.

(2) A high specific load capacity: The symmetrical design of herringbone gears offers a high surface area and an even distribution of load, meaning larger and more robust teeth may be used, making the design idea for transmitting high torque or power.

(3) A reduction in axial thrust: Probably the reasons engineers so favour the herringbone is that axial thrust can be reduced (in certain cases to the point of effective elimination).  With helical gears, the axial force imposed inherently acts to force gears apart whereas the herringbone gears have two helical sections facing each other, the interaction cancelling the axial thrust, vastly improving mechanical stability.

(4) Self-regulating tolerance for misalignment. Herringbone handle small variations in alignment better than spur gears or single helical gears, the opposing helix angles assisting in compensating for any axial misalignment, contributing to smoother gear meshing and extending the life of components.

(5) Heat dissipation qualities: The symmetrical structure assists heat dissipation because the opposing helices create a distribution of heat through a process called mutual heat-soak, reducing the risk of localized overheating, something which improves thermal efficiency by making the heat distribution pattern more uniform.

Gears: helical (left), herringbone (or double helical) (centre) and straight-cut (right).  Although road cars long ago abandoned them, straight-cut gears are still used in motorsport where drivers put up with their inherent whine and learn the techniques needed to handle the shifting.