Vincent, does the cover which you have, that is welded, have a manufacture's mark on it and if so what is it, please? I have just taken a cover off one of my U.K. made Stens with the dimple type attachment and with the manufacturer's mark of S106 and there is certainly no welding at all on this cover. From memory I think that all my U.K. Stens have the same manufacturer of cover but the Canadianicon Sten is likely to be different and I haven't had that cover off yet to see if there are any welds. The thing with form tooling is that it is not an exact science as you are trying to stretch and squash the metal all at the same time, in several different directions, and one of the potential problems is that the metal will sometimes crack/split as it is being formed. From personal experience I have normally found that this problem can usually be overcome by an increase in radius of where the metal is being formed in the tool. If your cover has a different maker to the example which I have been examining I would suggest that the manufacturer had problems with cracking of the cover while being formed and the simplest solution was to introduce 2 slits/cutouts into the blank followed by welding after forming. It is surprising that if one manufacturer found it necessary to introduce several additional operations which were not required by alternative suppliers.

Looking at the cover in detail I have to say that whoever the Toolmaker was for J. W. Spear & Son Ltd (S106) he/she made an excellent job of the tool. The tool has produced a very smoothly formed cover with very few ripples and bend marks etc which are sometimes seen on formed parts.