From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of American and British sheet metal practices, gauges, and costs for car body construction.
| Identifier | ExFiles\Box 178\2\ img074 | |
| Date | 7th March 1940 | |
| Serial No. 7 H.R. page 3 may be broken or strained out of shape by putting in an oversize sheet. There is a steady tendency to ship oversize sheets so as to do as little rolling as possible to the ton. In fact, we used to get five or six more sheets to the ton from American sources in the same gauge size. This used to be so here until about eight years ago, when C.U. started buying body sheet by the piece instead of by the ton. This immediately reverses the tendency, since the profit is then in supplying low tolerance sheets rather than high tolerance. The difference between American and British practice on a small body shell weighing 550-600 lbs. in the white, is something like 50 lbs., so that it is not to be sneezed at, either for cost or weight. 5) The Richard Thomas mill in S. Wales was the only mill who gave evidence of ability to supply real deep-draw sheet which would, for example make a front fender in one wallop without more than 2% rejects for tearing or wrinkling. The difference in cost and weight under these conditions is enormous. In the case of improper sheet quality, 50 hours of hand work and 30 lbs. of solder pops into the picture almost overnight. Richard Thomas were not particularly good at holding gauge size, but Vauxhall were keeping after them on an "educational" drive. 6) The British gauges follow a curve, while the American gauges are in two straight lines which happen to meet at 20 gauge. It thus happens that the popular body sheet thickness shows the maximum difference between British and American practice. As I recall (without notes), the British thickness for 20G. is .0396, and the American is generally given as .0375, but is actually 1.5 lbs. per square foot. Since the British sheet often runs .042, which is about 1.72 lbs. per square foot, there is actually about a 15% increased weight in this gauge size. V.H. Ltd. have a lot of notes and experience on this, and I think should figure with Manning in any drive you have in mind to improve coachwork. 7) Am going to irritate you further on the "loft layout" principle by sending you working details of the Cadillac monster drawing boards. Cadillac were pioneers of this system, which was introduced in chassis work about 1935, and is now used by everyone here. This is not the super high-priestly method of drawing on | ||