Value of British and Russian Timbers for Van and Lorry Bodies
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Characteristics of Some of the Woods that are Available and Suitable for the Construction and Maintenance of Commercial-motor Bodywork
By Eric Hardy, F.Z.S.
SHORTAGE of wood often raises special problems in the repair of commercial-motor bodies, particularly the platforms of lorries that have to stand up to abrasion and rough usage. For this type of work there is now generally available only home fellings and some imports from Russia and North America.
Platform timbers are exposed to the risks of dry-rot from the weather and if they be not of a naturally dyable sort they should be well preserved by boiling them in a tank of creosote for a few hours and then letting the timber steep in it overnight .as the tank cools down, in order to get a good penetration.
Most of the water-soluble chemicals used for preserving indoor wood against dry-rot are not of long service outdoors, owing to leechitIg by rain. The timber must also be able to stand up to rough usage without splintering, and in these days of air raids, when garages and sheds are liable to damage, it is an added advantage for it to have a natural resistance to fire.
Limited Home-grown Timbers of Value Few timbers would meet all those requirements, except, perhaps, woods like oak, jarrah, karri, teak and our native poplar. Of home-grown timbers being felled in war time, only about half a dozen are of much service for this class of work. Scots pine, spruce, poplar and willow will serve well for wood flooring or platforms, and oak or chestnut for underframes and chassis work.
Native Scots pine is not quite so strong as pre-war imported pine or the Russian pine now being imported, but it is only slightly inferior to Continental Scots pine and about equal to pre-war Baltic redwood. However, it requires a creosote preservative. Itis not a very heavy wood and it generally works easily.
Spruce is neither so strong nor so durable and is better used for flooring vans than open lorries, but it should be given a preservative treatment. There are many knots in spruce which make it difficult to work, and it is often sold as home-grown white deal.
Poplar and willow are good-wearing timbers. Poplar is well able to with stand rough usage without splintering, but it is lighter, softer and weaker than most hardwoods. 'Moreover, it is only half as strong and hard as oak, although it has the advantage of being 40 per cent. lighter, but proper seasoning Will make it just as tough as oak :and only 20 per cent, less stiff. Its mechanical properties are not so inferior when considered in combination with its light weight.
A good amount of the Douglas fir grown in this country and now being felled could be used in general commercial-vehicle construction, if preserved, for it is only slightly inferior to imported North American Douglas fir or Oregon pine.
Canadian birch would also prove suitable as a flooring timber for vans or other covered vehicles; its durability is limited in the open. Australian karri is a remarkably durable wood, which has the extra advantages of excellent bending properties—like native ash—so that it can be used for bentwork, but it is so delis& tough and strong that it is not easy to work.
A Canadian Wood of Durable Quality Canadian rock elm is another wood which is most suitable for bentwork and is durable. Native ash has to be properly chosen to give the best results from steam bending for bentwork, and even then it will require a preservative.
There is a good amount of native oak being felled, hut it should be remembered that it is the darker heartwood only of this timber which possesses remarkable powers of endurance. The lighter-coloured sapwood is not durable, and if any of this be included with the timber it will reduce its life considerably, unless it be well soaked in hot creosote, when it becomes as durable as the heartwood
When there is no oak available for frame and chassis work, a good native substitute is sweet or Spanish chestnut (not horse-chestnut). Although not quite so strong as oak, it resembles oak in its mechanical properties, but is somewhat lighter and easier to work. Horse-chestnut, common though it be, is not a suitable wood for -this type of work.
There are, of course, many more strong and durable woods of Empire origin which are quite suitable to the needs of chassis and frame work, but their supply is not regularin these difficult times. They include gurgjun, padauk, red seraya, Borneo and Burma teaks, Indian jarrah, Australian silky oak (suitable for bentwork), Indian eng, pyinkado, Canadian red pine for flooring, Andaman pyinma, and Australian Victorian oak or mountain ash.
Points to Remember About English Oak The average tensile strength of English oak is Si tons per sq. in., but, like Scots pine and Douglas fir, its weight and working properties vary with different districts of grciwth. Young oak is tougher and harder than old oak, but if it be dried too rapidly in kilns it tends to check very easily; it should not be dried at more than 105 degrees F. and not less than 85 per cent. humidity.
Most sorts of oak can be steam bent if desired, but they should not be used in contact with metal as the natural acids of the wood will affect the metal with which it comes into contact. Rock elm is preferable, however, for steam-bending. This has it greater tensile strength than oak-4 tons to the sq. in., and it is not quite so heavy. It is sometimes sold as cork, white or hickery elm, and comes from Eastern Canada.
All the British elms steam-bend satisfactorily but northern wych elm is stronger than southern red elm and might be useful for some chassis work as it has long seen service in wagon construction along with ash. It is not so strong as oak, being 30 per cent. inferior in bending strength and toughness, but Dutch elm is 40 per cent. tougher than common elm, and wych erm equals ash in toughness and oak in bending strength.