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).
Technical comparison of Gemmer and Saginaw steering gear components and manufacturing processes.
| Identifier | ExFiles\Box 173\4\ img153 | |
| Date | 30th November 1935 guessed | |
| -2- in a sticking point on the way back. This is difficult to believe and there seemed no evidence of it on the Saginaw gears. Against this is to set the greater angle of helix at the central position and the greater angle of pressure, which they agree may burst the roller and also result in wear. The greater helix might account for some of their increased reversibility. (Gemmer tight spot extends 90° either side of centre. They are finishing their rocker shafts with a very smooth finish obtained by a special grinding wheel). Another difference is that Gemmer do not cut their worm roller races eccentric to the worm, and do not seem to know about this. They said however, that they finish the worm with a cutter nearly exactly to the steering ratio in the centre, roughing out with one tooth more than the ratio. But I cannot find much evidence of this on the drawing. The machines are the Fellowes Generators similar to those in use at Saginaw. Gemmers shave the worm roller races and do not grind them. Saginaw are experimenting with this and seem to think they get better results. The Gemmer worm teeth are crowned .010, against the straight Saginaw teeth. Gemmer adjust the worm preloading by paper shims. They have a gauging machine which tells them the amount of shim needed to bring up the load. Except in one case, the rocker shaft has plain bearing and thrust, the latter being loaded by a set screw like the old Marles single roller type. They have also one large type in which they preload the worm roller bearings by a set screw at an angle. They use balls in the roller, except that they are developing a type with long needle journal bearings and plain hardened steel thrust washers. The object is cost only. They confirm what Saginaw and Olley assert, viz: the necessity of a short, very stiff, rocker shaft. I got out of Gemmers what I could not get out of Saginaw, viz: a practically complete set of drawings. I should say that Gemmers have attempted to ensure a constant preload on the worm bearings by Belleville washers, very high rated with an endwise clearance in position of .010, but they say they do not now make a point of this. | ||