DEMANDS UPON CHAINLESS CONSTRUCTION.
From this tendency to draw the two axles toward each other—which has to be resisted by the frame before there can be any effect to revolve the wheel—the chainless is wholly free. In so much as this, its case is proved at once. Yet, if it would be frank, it must repeat the common remark: “I have troubles of my own.” Making bevel-gears is a detail and may be waived; but when they are finished, other problems arise. These problems cannot be better stated than in the five sentences following, which come officially from the chief advocate of these gears and should be carefully considered:
“The maker must place them in the machine with perfect exactness. The front and the rear axle, with their gear attachments, should lie precisely in the same plane and exactly parallel with each other. Any failure to do this will result in binding, cramp, strain and unsatisfactory work. Not only must these conditions exist in the wheel as it comes from the workman’s hands, but they must be maintained under load and shock, under the severest uses. The frame construction must be so rigid that there will be no spring or yield under any strain.”
This is a statement of the contestant’s own advocate, who adds that the extraordinary weight of the old “League” chainless (seventy-five pounds at first, the reader will remember) was unavoidable because the makers had no way of getting frame stiffness except by putting in metal; he then argues that nickel steel now supplies the strength without sacrifice of lightness. Another advocate—an over-zealous one whom it is difficult to take seriously—declares that this make of chainless will never get out of line, and that if it ever does the running will remain unaffected. The jointed shaft of the [Bayvelgere] is designed to meet just this contingency. We do not predict, save to say that if the frame of any chainless with a rigid connecting shaft ever does get out of line there will be serious trouble necessarily. Make the “if” as emphatic as anybody pleases, and consider the danger of springing the frame however remote; the chance of this occurring, under some sort of conditions and usage, is one which the chainless, especially those of the bevel class, must encounter.
FIRST COLUMBIA REAR-DRIVER—1888.
As to any kind of construction, whether of frame or of driving parts, there is no trouble when spinning on a stand without a load; the question begins when power is put upon it against a heavy resistance in actual use. A maker who has criticised the bevel chainless more severely than any one else insists that bevel-gears are especially wasteful by friction. In his factory, he says, a power drill working with such gears will make only an inch hole through a certain piece of metal, while a similar drill without the bevels and run from the same shaft will make a 1⅜-inch hole through the same metal. But this is not entirely conclusive, and the appeal to general practice in machine shops does not count very much. It could just as well be taken against the chain, and against the spur gear, for the fact is that no gear is used there except when necessary. Whenever the shafts are a considerable distance apart the belt is used, which is simple, cheap and effective, developing a surprising amount of “bite” even on quite smooth surfaces. When the shafts are close together the spur gear is used, nothing else being available. When there is a distance and no slippage can be permitted the chain is the thing. When power must turn a corner it is a choice between belt or bevel gears. But to say that a thing is not good on a bicycle because it is not used to drive machinery in shops is poor reasoning. We might as well say that ball bearings are not good because they are never used on locomotives.
THE PROBLEM OF “END-THRUST.”
The objection of “end-thrust” is raised against the bevel-driver. If the reader will look at a cut showing the shaft in position with the two axles, he will understand that the large beveled wheel on the crank axle tries to push the pinion and shaft backward, so that it may free itself and turn as the rider is forcing it to do. This backward pressure is because the face of the tooth is sloping, and before the load can be moved this pressure back must be resisted solidly somewhere. So (it is said) the rear pinion of the shaft is liable to be forced hard against the one on the hub, thus causing friction and possibly “bind,” especially on hills and bad roads. But this peculiar action between the interacting teeth at the crank shaft is necessarily duplicated at the other end of the shaft, so that the backward thrust at the front is met by a forward thrust at the rear, the two thrusts thus counteracting each other.