If you are writing a book about materials, it should include products that exhibit functions which best exploit the material. As an example of a wood with good tensile strength, there can’t be many better examples than an archer’s bow, a wonderful demonstration of opposing mechanical properties in a single piece of wood.
The key to designing a bow is in understanding the contrast of tension that is needed on the outside of the bow – known as the backside – and the forces of compression required on the inside – called the belly. The traditional choice of wood for the elegant and flexible, traditional longbow is European yew.
A natural lamination process provides the contrast of the heartwood – the inner core of the tree – which displays good resistance to compression, and the sapwood – the wood near the outer part of the trunk – which has good elasticity in tension, which means that a single piece of yew fulfils both of these physical criteria. When other woods are used in bows, designs sometimes feature a composite of wood varieties. In some instances, hickory is used on the backside and hornbeam for the belly side. In Asia, a combination of horn on the belly side and animal sinew on the backside gives the bow an explosive shot. As with many natural materials, wood has more recently been replaced by sophisticated composites of carbon and fibreglass in contemporary archery competitions.
Image: Yew longbow
Key features
•Comparatively heavy: 670 kg/m3 (42 lbs/ft3)
•Extremely hard
•Excellent elasticity
•High density
•Good stability
•Reasonable staining
•Finishes well
•Steam-bends well
•Moderately difficult to work due to its irregular growth and shape.
Sources
Throughout Europe, Scandinavia, Algeria, Asia Minor, northern Iran, the Himalayas and Burma.
Cost
Yew is fairly common and reasonably priced but, as yew trees are comparatively small and irregularly shaped, large pieces of yew lumber are rare and therefore can be pricey.
Sustainability issues
There are fewer yew trees now than previously, as with many natural species utilized by mankind. Considering the great strength, durability and beauty of the timber it could be seen as a shame that many of the uses for which yew was perfect are now met by iron. The species is further threatened by felling, partly due to rising demand from pharmaceutical companies that extract an anti-cancer property, Taxol, from the leaves of cultivated species.
Production
If balsa and lime are the soft hardwood, then yew is the hard softwood, making it a difficult wood to work. Yew also sits together with ash, birch, elm, hickory, oak and walnut as a good wood for steam bending. This is a process that can be done as an industrial production or in a home workshop.
Typical applications
Since the time of the ancient Egyptians, yew has been a symbol of everlasting life and this is why you are likely to find so many yew trees planted in churchyards and cemeteries. As such, it has often been referred to in literature, ranging from the yew bows referred to in Tolkien to the yew wands in the Harry Potter series. Beyond this, it is very good for turning and furniture, and it also makes an exceptionally decorative veneer. It is the wood traditionally used for Windsor chairs.
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–Excellent strength and elasticity –Good stability –Very good steam bending –Highly decorative |
–Difficult to work |