Composite versus
Page 42
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All-metal' Bodies ti.A JOINT paper on composite, or anmetal bodies, by Messrs. Charles 1-f. Roe and B. Homfray Davies, is divisible into separate contributions.
Only a few years ago bodies were almost entirely of timber. The mortised and tenoned joint, the' halflapped joint, tonguing and grooving of roof and floorboards were all employed during the early days of busbody development, and they still persist, whilst the use of iron and steel for ✓ einforcing gradually grew.
• The petrol bus appeared about 1896. This gave scope in design and was the stage at which the composite body really appeared, but not much consideration was given to the powerweigh factor as most modem alloys were not available. • How Bodybuilding Progressed.
At the immediate post-war period, structural framing had made little advance, but improvements in thin steel sheets made these an alternative to mahogany panels.
Then there arose a demand for light bus bodies, and aluminium in thin sheets and extruded .sections began to be utilized for panels and mouldings.
The intensive development of the bus attracted newcomers, many lacking experience in producing the complex article involving many, trades and materials. Municipalities often entrusted the manufacture of bodies to firms with neither adequate experience nor facilities, and inferior bodies were frequently put into service.
The author has heard it stated that timber is liable to rapid deterioration. This is a wild statement. Failure has often been due to foreign and inferior ash. Sometimes kiln-drying is used. This drives out the sap essential to its preservation. The selection of English naturally seasoned ash, if properly protected during manufacture, will give a timber lasting for many years.
Teak framing will outlast any period of life demanded. Can this claim be made in respect of the thin sections used in metal construction where any corrosion is vital, and who can suggest that protection will be more carefully carried out in metal bodies than in the case of 'timber?
He has examined metal bodies where half of the members has been broken or cracked, and there were many instances of this in a lesser degree.
In proportion to use, complaints against the metal body are more numerous than with the coachbuilt. Many are standing up well, but does this not equally apply to good coachbuilt bodies, which are being produced in ever greater numbers? . .
It has been the "object to develop bodies on lines of symmetry and beauty, and Mr. Roe claims that more satisfactory results ran be achieved in the coachbuilt type, although metal bodies are improving.
Interior finish of the standard required is easily obtainable in the composite body. There is no comparison between natural wood and metal finish. Walnut has its beauty enhanced by polishing, but steel painted walnut is, at best, an imitation. He believes that builders of metal bodies are reverting to genuine wood schemes for interior finish. Mouldings can be fixed more readily to wood than to steel, and where notice-cases, lockers, etc., are required, there is no difficulty with wood. but with metal they are numerous.
Small quantities of metal bodies cannot be produced so cheaply as the composite, and it is believed that a similar claim applies for quantity productiOn. In the modern factory all parts for framing are accurately produced to jigs, and the author would guarantee to mass-produce a composite body on the same relative terms.
He contends that the composite type is more easily and efficiently adapted to suit individual needs, whilst maintaining the fleet standardization desired by each operator. Sections can be made which it would be virtually impossible to produce in steel.
A Comparison of Maintenance.
In respect of maintenance, where first-class construction applies in each rnae, the author does not suggest that there is much difference, but if maintenance has to be carried out, this is more readily and economically done in the composite body.
. As to accidental damage occurring.in examples Mr. Roe has investigated he would vote in favour. of the COMposite body in respect of ease and cost of repair. The operator can produce from the raw material many of the structural parts, or obtain them short notice. In collisions the damage is confined almost., exclusively to • the point of impact.' whereas in the .metal frame, the shock may be transmitted over a greater area and cause increased distortion.
The contention that the metal body is immune from fire is groundless. The danger lies in the inflammability of the fuel. Floorboards would be the first to ignite, and these are of the same material on both types.
In summing up the author claims that discerning passengers appreciate riding in composite bodies, due to the absence of drumming and other unpleasant noises.