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).
Methods for securing studs with screw threads, particularly in metals other than aluminium.
| Identifier | ExFiles\Box 148\5\ scan0262 | |
| Date | 23th December 1937 | |
| To By.{R.W. Bailey - Chief Engineer} & Rm.{William Robotham - Chief Engineer} ? 1280? RHC.{R. H. Coverley - Production Engineer}1/LS.23.12.37. SCREW THREADS. In reply to BY.8/G.19.11.37, we have considered the question of studs screwed into metals other than Aluminium, and the following are our conclusions with regard to the proposals put forward:- 1. The present system of using studs produced from centreless ground bar, undoubtedly represents the most economical proposition, and provides satisfaction in service. For all normal purposes the lock given by tightening the last thread of the stud against the tapped hole appears quite sufficient, and very few cases are encountered of studs becoming loose when nuts are being removed after service. The wedging action of the last thread on studs fastened in this manner causes some local disturbance of the surface metal, but this can usually be overcome by countersinking the hole slightly before tapping. 2. The question of securing studs solely by the interference between the male and female threads has already been tried out on Wraith main bearing and cylinder studs, but it was found impossible to maintain the required interference fit, and the scheme was therefore abandoned in favour of shouldered studs. Admittedly in this case the studs were screwed into Aluminium, but it is considered that the same trouble would occur in varying degrees with other metals. Tests have revealed the fact that a series of holes in a metal plate tapped in the same manner and by the same tap, vary in effective diameter by as much as .002 without apparent reason, furthermore, the effective diameter of the stud threads cannot be controlled within .0025 of size unless screw milled or ground, hence it is obvious that any predetermined interference can only be maintained by resorting to expensive manufacturing methods as in the case of valve seats. Should studs be screwed into a block without any definite stop i.e. relying on the tight fit of the thread it would be necessary to provide fitters with a number of height gauges with consequent risk of incorrect assembly. It is therefore considered that it is impracticable on a production basis to rely solely on tight threads for retaining studs. | ||