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The History of Wood Bearings
The old caveman cartoons notwithstanding, Wood is arguably
the oldest bearing material on the planet - in continuous
use since the invention of the wheel. In fact the first
known wheel was several planks of wood, fastened together
crosswise, then rounded on the perimeter. (The stone double-wheel, pictured at right, was less than successful for a variety of reasons.)
Warriors
in ancient Rome drove chariots with wooden bearings
lubricated with animal fat; Marie Antoinette would have
ridden to her untimely end in a cart whose axles were
born in wood. Bearings made of lignum vitae
bore the rudder shafts of ships in the golden age of
sail, and when the steamship rose to power, its propellor
shaft spun in lig bearings, too.
Despite Isaac Babbitt's invention of a revolutionary
metal bearing alloy in 1839, wood remained popular,
and continues to this day to be the most "shaft-kindly"
bearing material available. Even the latest engineering
plastics fail to protect metal shafts as well as wood.
There are innumerable historic examples of wood bearing
use, only a few of which we've mentioned here.
Even long after metal, rolling-element bearings became
the de facto standard for industrial machinery, wood
has continued to be used as the bearing of choice for
a great many machines. Woodex still receives calls from
folks looking for replacement bearings for their old,
Sears snowthrowers, or for old farm implements. We've
built replacement bearings for the water wheel in a nineteenth-century
grain mill, and we're often asked to make replacement
bearings for hydroelectric turbines. We've applied our standard wood spherical pillow block bearings to an aesthetically-pleasing Micro Hydro installation in Ireland. We've even made bearings for a modern, floating-arm trebuchet built by East Coast Catapults - a team of engineering students at McGill University. You can see it in operation here: Treb Movie filmed at the Canadian Wood Council's First Annual Engineering Competition in 2004, at Carlton University in Ottowa.
Wood is a fairly rugged material for low-speed, low
load applications, and in many cases it's possible for
a user in a remote location to fabricate a rough and
ready bearing on site that will last many months or
even years. Because of it's near-universal availability
and ease of shaping, wood is gaining new favor in third
world countries where metal bearings can be prohibitively
expensive.
While Woodex still builds the occasional lignum
vitae bearing for water-immersed applications,
this extremely dense (it won't float), slow-growing
hardwood has been lumbered off. Though not extinct,
the trees take three to four hundred years to mature,
and only small cross sections of the wood are available. Woodex occasionally makes jackstaff halyard bearings from this material for U.S. Navy submarines.
For those curious about lignum vitae, Woodex
uses a species called, Guaiacum
Coulteri. This wood has a beautiful blue Flower.
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