Gauges Guarantee Interchangeability in Bodywork
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London Transport Adopts Means Which Provides Check on Mating of Body to Chassis AS may be well known, London Transport was, during the war, the parent concern of the London Aircraft Production Group, and as such, became responsible to the Ministry of Aircraft Production for the design and supply of what were known as interchangeability media jigs for the Halifax bomber.
As the result of the experience thus gained, the Board made arrangements at the end of the war, to produce a master chassis jig which would ensure the complete interchangeability of chassis, an essential to the system of maintenance and overhaul which obtains at the Chiswick works of the organization.
Rigid Tolerances .
It will at once be appreciated that this necessitates the adherence to a rigid standard of tolerances which, however, is not intended to imply small tolerances. Such a master jig would merely set a limit to the extent of the permissible variation acceptable in practice, so that provision might be made in the design of the chassis and body in order to ensure that no difficulties are likely to arise during assembly.
Before the jig could be designed. sketches were made of the chassis and lie complete body, the dimensions and features which directly reacted upon assembly and mating being indicated. AU dimensions which were subsequently used had plus or minus limits imposed, which could be interpreted as extremes within which components could be built.
In determining these limits it was necessary to make the tolerances as large as possible to assist production, and if the examination indicated that certain tolerances were undesirably • tight, detailed design had to be reconsidered with a view to making them easier.
In applying this procedure to chassis production, it will be evident that all contra', dimension.; must fall within the agreed tolerance limits. Accurately to check all the relevant dimensions with standard equipment is difficult, if not impracticable, when quantity production is concerned. With the special chassis gauge which has been designed and made, inspection of all major locations can be carried out within an hour.
Tubular Construction The gauge is of tubular construction and is fitted with master datum points, from which all vital points can readily be checked. In use it rests on the two front and the two, rear body-brackets, and it takes its location from the front and rear body-mounting dowels.
It has been designed to clear all points of the chassis, with sufficient margin to ensure that it may be applied to a chassis even though the latter might vary from the correct dimensions. Even when one or two features of the chassis are incorrect, it is thus still possible to apply the gauge and complete the inspection, the incorrect features being subsequently rectified.
Gauge Checks Some of the points which are checked by the application of the gauge are shown in the accompanying illustrations, but the complete series is as follows:— (1) The centres, diagonals and level plane of four main body-mounting brackets and dowel holes in order to make certain of the correct mounting of the body.
(2) Position of radiator in three planes to ensure correct clearance around the cab, and correct fitting of the bonnet.
(3) Position of steering wheel in three planes as a check on correct clearance in the cab.
(4) Vertical alignment of engine to ensure clearance between rubbermounted unit, and the side shield of the cab.
(5) Position and altitude of drivers' floor-plate, which affect correct mating with cab and rear floor-plate.
(6) Location of fuel-pipe union to ensure correct assembly with pipes on body.
(7) Position of oil reservoir; this governs clearance from body bar.
(S) Position of fuel-tank filler, to ensure alignment with opening in valance panel.
(9) Alignment and lateral position of rear axle as a check on the overall width of the vehicle and to ensure that • the correct clearance is provided for the wheel arches.
In practice, the assembled gauge is lowered on the chassis by a roof sling, but it is capable of being applied in sections light enough for man-handling. In its sectioned form it can be conveniently transported.