Precision Methods in anufacture Behind a British-buil Tractor
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What was Revealed by a Recent Visit to the Works of David Brown Tractors, Ltd., which Builds Not Only Tractors But Also a Range of Implements for Agricultural Work
VASTLY increased production of tractors is being pushed forward in various parts of the country, and when a representative of The Commercial Motor visited the recently established works of David Brown Tractors, Ltd., at Meltham, some rewarkable changes were in evidence. Drastic alterations had been made to premises that formerly were used for an entirely different industry.
High-class precision tools and conveyor lines are ranged to facilitate flow production. But for the advent of this new industry many local people might have been unemployed. Now, however, work is being provided for all persons in the locality who possess suitable experience, or who belong to types likely to respond to specialized training. Given the required raw materials some 100 tractors a week may reasonably be expected from this plant in 1941.
Whilst the main aim of the factory is to assist the agricultural industry A44
and other spheres of national importance, it is not intended as a purely war effort, because growing world demands for tractors indicate the presence of an attractive post-war e-cport market that, hitherto, has been dominated to a considerable extent by America.
In many colonial markets Brits manufacturers are given an advantage as a result of the difference between the cost of petrol and that of paraffin. In the United States this difference is negligible, so that American tractor designs are favouring the use of the car-type engine. A further factor is that the market is tending to classify itself into a limited number of types ' and in 1999 some 80 per cent, of American production was actually concerned with two sizes. The great bulk of them were the popular 25 h.p. to 30 h.p. models and it is interesting to note that the David Brown tractor falls directly into this category.
Agriculture is an industry in which it is desirable to have service facilities always available in the farmer's own locality and the lack thereof may be nothing short of disastrous. The distribution system is now well in hand and efforts are being made to line up the most suitable dealers in those districts remaining open.
David Brown Tractors, Ltd„ of
course, produces not only tractors, but also a range of tillage implements, so that equipment is available for many needs of power farming. Additionally, the specification of the tractor is planned so that the machine can be easily adapted for various industrial purposes.
Frequently, the layman fails to appreciate the amount of work that is essential to ensure reliability in a machine that, in many ways, has to meet unique demands. The fact that it is impossible to stipulate a running-in period means that there must be greater accuracy in manufacture and greater care during the testing of the engine, than is usually the case in car manufacture.
Thus it is that the engine test probably occupies three times as long as that of the average motor manufacturer. This care is particularly important because the tractor is usually running at 80 per cent. throttle opening and that is why the oiling system has to be far more consistent and capable of handling overloads than that of the motorcar.
Much the same remarks apply to other components. For instance, the load on the low gears, so far as duration is concerned, is something like 10 times higher than that dealt with by an ordinary commercial gearbox. Typical tractors perform something like 1.500 to 2,000 hours work in a year, which is the equivalent of running a road vehicle up to 60,000 miles, but reliable types, nevertheless, will still give • two years' service without overhaul.
All these factors have to be taken into account when planning manufacture, but the makers have an important advantage in that they are dealing with a basic factor, earth, which remains constant, so that once a sound
design has been established, changes are slow and it is possible to tool up for years ahead
The power unit of the David Brown tractor is a four-cylindered o.h.v. unit with a bore of 3/ ins, and a stroke of 4 ins., and it is fated with liners. For agricultural work it is governed down to 1,300 r.p.m., but for haulage and other faster duties this can be increased to 1,800 r.p.rn. On agricultural work this gives ploughing speeds of 2.2 m.p.h. and 9.2 m.p.h., with 4.5 m.p.h. in medium gear and 9.5 m.p.h. in top gear, whilst the proportional speeds obtainable with the faster governor setting are adequate for haulage needs.
The wheelbase of the tractor is 64 ins, and the track is adjustable between 44 ins. and 60 ins.; the turning radius is 8 ft. 6 ins. Wheel equipment includes patent common centres for pneumatic rims, for steel wheels with 5-in, rolled-section spuds, or for
spud-rings. The driver's seat is comfortably upholstered and the controls are easily accessible, special features being an independent clutch which can be worked from the rear while attaching implements and independent hand brakes to facilitate quick turns. Independent power take-off and pulley units are available, if required. In addition, there are basically similar machines supplied with tracks instead of wheels.