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).
The materials and production methods for hourglass steering worms, comparing Chrysler and Gemmer practices.
| Identifier | ExFiles\Box 153\2\ scan0354 | |
| Date | 12th July 1937 guessed | |
| PRODUCTION OF HOURGLASS WORMS. The material in use for the production of hourglass steering worms is varied by the different concerns visited. The use of S.A.E. 5130, a chrome-manganese, with a .30% carbon content is preferred by Chrysler, they produce the piece from bar stock which is heat-treated to give good machinability and aids as a stress relieving property. The bar is fed to an automatic lathe (Fay-Jones & Lamson) upon which the worm blank is produced. The turning of the bearing cones at either end is performed upon a small converted centre-lathe, followed by burnishing of the tracks, to eliminate grinding, and facilitate good cone location for worm generation. The pilot bore, which is produced upon the automatic, is used for broaching of the bore, designed as the fine serrated type using master key for angular location on both cutting and assembly. The method of cutting employed, is to rough the worm upon a thread generator and finish upon a similar machine with modified cutter form, alternatively finish cutting is done upon a converted Gould & Eberhart hobbing machine, adopting reversed conditions to the conventional machine. The result of these cutting methods show speed of operation but accuracy cannot be claimed by either of these methods. The heat-treatment and hardening is carried out by heating the finish cut worm to 1,550°F in a cyanide or activated bath and quenching in oil, tempering of the stock not being employed. The operations of production used by 'Gemmer' steering are approximately the same as Chrysler, except the stock has a different analytic composition, being a chrome-moly steel. The methods for cutting follow closely to the Chrysler practice, but with the introduction of a burnishing operation following the final cutting of the worm. The operation is performed upon a rig approximating steering conditions, with the burnishing roll passing through the same line of action as the follower in normal conditions. continued. | ||