WORM VERSUS CHAIN TRANSMISSION.
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The Cudgels are Again Brandished on Behalf of the Worm Drive in Answer to the Attacks of the Protagonist of the Chain.
By "A Worm-drive Enthusiast."
VVHEREAS one "Chain Enthusiast," he the issue • of The Commercial Motor for July 14th, makes statements purporting to refutef the arguments advanced in rep13, by the undersigned to his original assertion (viz, and to wit, that the chain drive constitutes, in excelsis, pro bone publico and sine qua non, the onlyoerfect transmission for vehicles of whatever kind you care to mention), I, " Worm-drive Enthusiast," by editorial grace, beg leave to return to the_ fray in terms substantially as follows :— After disclaiming any abusive intent (for Brutus is an honourable man) and appreciating that delicacy of -sentiment which shrinks from subjecting a sensitive soul (such as mine) to the pangs of disappointment, I rise to remark that all that "Chain Enthusiast" has succeeded in bringing to his aid are— (a) One 300 h.p. Fiat car.
(b) One chain-driven locomotive.
In re (a), it need only be said that, with • 300 h.p. available, there is Margin enough to permit experiments in chain drive to be made. On the other hand, if support is,to be drawn froni the racing track, an equally forcible argument fon the worm drive is provided by the A.C. car, which with only 16 rated h.p. possesses more than th9 usual share of world records and indulges in trips up Snowdon and similar exploits by way of relaxation.
In re (b), the existence of a chain-driven locomotive is not an argument—it is an anachronism.
"Chain Enthusiast's" gratitude for the conces-, sion of the chain to bicycle transmissions seems to come with a slight effort; possibly he has experienced the joys of an unequally stretched chain which is too tight in one position and falls off in another. It is a thing which might happen to anybody ; but, in any case, the fact that shaft drive has been tried on motorcycles does not put the transmission of these Instruments of torture on all fours with that of a car or lorry ; if it did, inquiry would probably bring the Jolly old roundabout and Mr. Robinson's pea-splitting machine • into the discussion.
The Ford—one of America's Few Wormdriven Chassis.
His ungracious reference to the Ford clearly shows either that he has entirely missed the point and object of the allusion or that, with politicianlike skill, he has endeavoured so to twist the matter as to confuse the issue. Let eme remind him that the reference Was not intended as an argument in direct support of worm drive ; it was merely introduced with a view to shedding some light on the "chain drive is cheap" argument. Others might deal with the point by quoting a hackneyed catch-phrase, but this I scorn to do.
Reverting to the application of the chain anti worm drives to the pleasure-car chassis, " Chain Enthusiast" can adduce nothing, for all his enthusiasm (apart from the 300 hp. car, to which the adjective " pleasure " is scarcely applicable), in support of the chain, save some statistics showing,that the worm drive is not used in American practice, but these statistics still more completely devastate his original thesis that the chain drive is superior to the shaft drive. The absence of worm drives from American pleasure-car chassis only shows that American designers have their own prejudices—prejudices which, but for the progressiveness of a few rna,nufacturers (who have prospered accordingly), might 'still extend to coinmercial vehicle builders in that country. It certainly does not prove that the worm drive is unsuitable for pleasure-car chassis, for at least one car manufacturer .in this country finds the silence of the worm a valuable selling point. What of AC., Daimler, -Hillman, Lauchester, Rover, Standard, Vulcan and Wolseley?—a list which is sufficiently representative of every type of pleasure car (taken in conjunction with the high standard of engineering skill associated with these firms) to show that the worm drive is not% freak but "a thoroughly sound and accepted form of transmission in pleasure-car practice. Can the chain show such a list? For all his examination of statistics, " Chain Enthusiast" has failed to fill the hiatus to which I have drawn attention.
The Chain as a Component in Double Reduction.
In the matter of double-reduction drives, " Chain Enthusiast," making full use of his natural gift for rhetorical 'contortion, skated round the question in a manner satisfactory, to himself, no doubt, but perhaps not to others. That a double reduction possesses advantages when appliedeto heavy vehicles and high engine speeds is no reason for the universal employment of a chain-cum-worm or bevel. In any case, the right-angle drive is necessary (given a longitudinally disposed engine axis), and it is only when the total reduction required is greater than can be provided by a single stage, or when, for any other reason, two stages are desirable, that the chain has any particular claim for consideration, and then only as a competitor to the simple and more efficient spur gear. The fact that double reduction gives a lighter differential cannot, by any flight of imagination, be claimed as a virtue of chain drive per se, for a double reduction can be designed quite nicely without chains at all, thank you.
The horrible state of affairs which "Chain Enthusiast" pictures as existing in worm-driven rear axles would, if true, put the manufacturers thereof out of business (and there are no signs of such a thing occurring just yet, anyway) and the chain makers would be gloriously overwhelmed. Yet, still the trend from chain to sliaft drive continues, even in the last stronghold of chain drive : the steam wagon. Possibly his picture is somewhat out of perspective—but maybe he regards this as being offset by his literary style. Not to be outdone. I have asked Miss Edith Noveletto to give a pen picture of a chain drive, and with her permission I reproduce this masterpiece below. It is entitled— The Weakest Link—or, Mud is thicker than Water.
"It was a dark and stormy night and shrieks and groans emanated from a solitary bevel box and differential gear, the shaft alignment of which, lacking universal joints, was, at the mercy of every strain in the chassis. Perched precariously on a cross-member, -it was beyond the powerAof Mont morency de Trafford (for that was the driver's name) to bring the gentle influence of a spanner to relieve its distress. The ghostly clanking of the chains, exposed to all the fury of the elements, and their weird serpentine undulations careering madly between the sprockets, lent a note of horror to the scene.
"The five hundred and thirty-seven parts, of which, in round figures, two hundred and twentynine were under load, stretched and wore under the influence of the mud and water which, although constantly dripping, lacked the lubricating qualities of even that substance. Nevertheless, the efficiency, determined at all costs to maintain the principle of 'Truth in Advertising,' remained at 99.9 per cent., rising to 100 per cent. when, wearied by a life of suffering and anguish, the chain fell to the ground with a sickening thud.
"One of the prettiest funerals of the season was that of Montmorency de Trafford, Who, of course . . . .
Incidentally, parenthetically and by the way, I do not remember ever seeing a claim for 97.31 per cent, efficiency made for a worm drive in practice. The records of the N.P.L., of course, include the value of 97.3 (experimental accuracy 0.1 per cent.), and many of more than 97.0, but both Mr. J. W. Hobson and (I believe) Mr. H. Kerr Thomas have obtained overall efficiencies of 96 per cent. for a-worm gear as mounted in actual practice. Moreover, I noticed in current advertisements in The Commercial .1,fotor and also. in American journals, that individual worm drives have run satisfactorily for 250.000 miles. What are the best-figures available for chain drives?
"Chain Enthusiast's" flippant dismissal (it is very wrong to be flippant !) of "those horrid accelerations and decelerations" (horrid is the word) causes a smile. The risibility is, as it were, good. A thing does not vanish by being dubbed "highbrow," unfortunately. If such were the case the adjective would find extensive application— even to enthusiasts—what? If I found myself falling off the Woolworth Building, would I derive much comfort from the reflection : "No, no ; this sinking feeling is due to an acceleration—a trifle— merely a highbrow application of Newton's law of gravitation "? I think not—I would dismiss such airy speculations and come down to earth. "Chain Enthusiast" persists in his generalities on efficiency and for lack of convincing argument implies ignorance in his opponent. 01 unworthy ! Fie for shame ! Dismiss the idea of "laboratory efficiency" (which was introduced, be it noted, by " C.E." himself) and balance these points : A Chain Drive.
(a) Depends for its lubrication on good luck (often conspicuously absent).
(b) Is at the mercy of the elements (see thrilling quotation above).
(c) Has bearings the alignment and centre distance of which are always changing, whilst the chain describes a path which delights only a mathematician.
,d) Is silent — sometimes.
I ask you, in which case is the efficiency—from a practical aspect, mark you—likely to be best maintained? No prize is offered for the first correct solution received before 1927, accompanied by the full name and address of the competitor.
Brother "Enthusiast," fare thee well!