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).
New worm gear record and a discussion on the economic considerations for automobile engineers.
| Identifier | ExFiles\Box 37\1\ scan 215 | |
| Date | 18th February 1920 | |
| February 18, 1920. 117 The Motor NEW WORM GEAR RECORD.—Contd. Worm wheels, like worms, are cut by a generating process. This is performed by means of a hob which resembles a finished worm, except that it is gashed along its length to provide cutting faces. The worm wheel blank is mounted on a revolving table which is driven at a speed varying according to the ratio of the gears being cut, whilst the hob travels longitudinally across the face of the wheel. Owing to the spiral of the hob, this travel has to be compensated for by means of a differential. The final operation is performed with a patent reamer hob, which ensures a perfect shape of tooth with a smooth surface. The company also manufacture special machines for correctly testing their worm gears. The bed of the standard machine consists of two slides at right angles, one carrying a pair of adjustable centres, whilst the other carries an adjustable arbor adaptor, the latter controlled by a micrometer screw, which enables it to be set at any required distance from the worm shaft, thus giving correct centres for the worm and wheel undergoing test. All worm wheels must be absolutely interchangeable, and they are measured by means of a double ball micrometer, which gives the comparative thickness of the teeth on the pitch line. Another small instrument is used for measuring the relative thickness of the thread of the worm. The worm to be measured is placed upon two rollers, a third is then placed above, and the overall distance measured on the clock indicator. The instrument is calibrated in the first place by a master worm, and all others to the same specification must give the same reading, and are thus interchangeable. It is important to note that it is impossible to introduce hand work on the new type of gear without spoiling the tooth contact, and in this connection it may be remarked that at previous tests which were carried out by the National Physical Laboratory, a representative of the Laboratory witnessed the final stages of manufacture, sealing the gears as they were taken off the machine, and with these same gears efficiencies up to 97.3 per cent. were obtained. The severity of the tests on worm gears depends to a great extent on the temperature of the lubricant used. The higher the temperature of the oil the more difficult it is to maintain a perfect oil film between the teeth. The oil used on the tests for the previous world's record was at a temperature of between 30 and 50 degrees Centigrade. In the tests of the new gear the oil was artificially heated so as to maintain a temperature of between 50 and 60 degrees Centigrade; thus the results are even more conclusive, as the conditions were more severe. The lubricant used for the whole of the lastest tests of the F.J. worm gear was Duckham's D.B.S. oil. Typical David Brown F.J. Type worm gears. ECONOMICS AND THE AUTOMOBILE ENGINEER. The Need of a New Outlook. IF any doubts had existed in the minds of the Automobile engineers of this country as to the way in which their efforts should be directed at the present time, recent events should have settled the matter in a decisive way. The obvious and outstanding aim must be economy; not only in production but in power and in performance. We have repeatedly urged in these columns that the artificial prosperity of the moment should not be reflected by undue elaboration in design. We have pointed out that the old definition of an engineer as being “a man who can do for a shilling what any fool can do for half-a-crown” still holds good. It applies to-day with exceptional force. Automobile engineering in this country stands or falls henceforth by the criterion of cost. Cost of production is important, cost of maintenance to-day is vital, but in no department can the subject be ignored. Now, some engineers seem to be so engrossed in the mechanics of their craft that they are inclined to neglect its economic aspect. Surely that is a very great mistake. Mechanical problems crop up, are solved, and become problems no longer. But the economic problem remains. Like the poor, it is always with us; and in proportion to the comparative poverty about, so it becomes acute. It is particularly acute just now, and so far as can be seen, will not be quickly solved. Hence the great need of concentration on the subject. For some unexplainable reason, questions of cost have not been very popular in some of our engineering institutions. The very mention of such a sordid subject in the lofty scientific atmosphere with which they are pervaded would almost seem like sacrilege. It would be like discussing the price of butter in a drawing-room—taboo—not done. Money and mechanics do not mix. But in the future a different attitude is needed. Economics and engineering are to-day inseparable, and every engineering problem has an economic aspect which must be considered. To such considerations we commend the attention of that institution to which the automobile industry already owes so much. D19 | ||