The principle of constant wall thickness

Abstract

The aim to make everything as simple as possible for the workshop leads to a basic rule of design—the principle of constant wall thickness. This means that hollow parts and flat or ribbed workpieces produced by casting or welding should preferably be made with a given uniform wall thickness. Seen from the functional viewpoint, there is in fact everything to be said against such a rule—take, for example, the strength characteristics of the pressure vessel seen in Fig. 100. According to the ‘boiler formula’ this ought to be made with a number of differing thicknesses δ, matching the diameter d at various points. Since d₁<d₂<d₃, we should make δ₁<δ₂<δ₃. The flat base to the left is a case of its own, and ought according to theoretical mechanics to be especially thick. In spite of these reasons for varying the thickness of the wall, the container will probably be made with a uniform wall thickness, apart from the flanges which are particularly heavily stressed. Just how natural it is for a designer to keep to the same wall thickness can be seen from Fig. 101; here every section of wall ought properly, from the functional viewpoint, to have a different thickness—and yet more or less the same thickness has been used throughout.