THE QUESTION OF THE GEAR TEETH.
The endurance of the gear teeth is also a question to be decided by use. It has been said that “the teeth are so designed as to be relatively stronger than the cranks and under excessive strain the cranks will break first;” also that “the individual parts are stronger than the elementary parts of the chain.” We have seen cranks tested, in regular shop routine, by samples taken out of each small lot, under a measured load of 1,000 pounds, and have seen them show their quality by returning to the straight line when the load was removed. The cross-section of an average crank is three to five times that of a bevel or radial tooth. In practice, cranks do not break; some other part, less strong, breaks when something must, and so the statement that the bevel tooth is stronger than the crank which is to be measured against it under load seems rather too forcible. The comparatively slight tooth must bear the same strain which comes on other parts and the very small though real bit of elasticity or “give” which the chain possesses, by virtue of being made up of many parts joined together, is lacking in gears of any kind; the strain on those is “solid” and unrelieved. The fact that breakage of a sprocket (unless by some collision or extraordinary fall) is a mishap almost unheard of does not insure the gear tooth in the least—the two are not the same case. The sprocket tooth is very thick in the direction of the strain, and the pull of the chain comes on not less than five teeth at once on the rear sprocket and twice as many on the front, thus dividing the load; the gear teeth, on the contrary, are thin, and the strain is concentrated on not more than two at a time, practically upon one. Yet we must distinguish here the bevel and the spur-gear tooth from the peculiar teeth on the pin-roller gear; the latter are so thick that no doubt of their strength need be raised.
DEFENDER MIDGET—1898.
The last paragraph is not to affirm or to imply that the teeth will not prove equal to their task. But such gearing has never been used on cycles; the bevel wheels of the tricycle “balance-gear” were larger and were not common enough to constitute an exception. Spur gears have been successfully used for many years on the Crypto gear already described, but four pinions are employed on that instead of one, for the express purpose of dividing the strain. So it is fair and well to note that when we resort to gearing as an escape from the chain we are going from the long-tried to the untried.
Here it may be in point to quote from the current advertisement of one of the oldest concerns in the English trade, the Centaur Company of Coventry:
“The pioneers in the cycle trade can afford to view with equanimity the appearance of the faddist who, from time to time, tries to resuscitate some obsolete and exploded notion which, in the early days, has already been thoroughly tested and abandoned. The Chainless Safety, with which we have been threatened during the past two years, is an example of this. Bevel-gears, spur-gears, roller-gears, rod-and-piston-gears, intermediate wheels, and every conceivable form of gearing were experimented with by ourselves and many of the older makers in the early ’80’s, for the purpose of dispensing with the chain. If, as a medium for transmitting power, they were then found to be inferior to the crude and imperfect chain available at that period, it must be manifest to everyone who is familiar with cycle construction that, with the perfect chain of today, the comparison must be still less favorable to the chainless methods.”
This is not quoted as endorsing it, nor do we regard the experimenting mentioned as conclusive; the point lies in the last sentence. For while it is true that the cutting of bevel or radial gears has been so much improved that the results of trials long ago do not signify (as is frankly admitted by not over-friendly English trade journals in commenting on the [Columbia]), it is equally true that the chain also is greatly improved.