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Wheels, Ancient and Modern.

13th April 1911, Page 4
13th April 1911
Page 4
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Page 4, 13th April 1911 — Wheels, Ancient and Modern.
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Which of the following most accurately describes the problem?

With Particular Reference to the Use and Merits of Wire Suspension Wheels.

Mr. Henry L. Heathcote, B.Sc., the Chief Research Chemist of Rudge-Whitworth, Lid., on Wednesday the 5th inst., at the Royal Society of Arts, contributed a most-interesting paper on "Wheels, Ancient and Modern, and Their Manufacture," and, in the course of his remarks, expressed the opinion that those who seem most competent to judge agree that wheels took their origin from cylindrical tree-trunks which were placed as rollers under loads. He thought that pro bably the first type of vehicle was a sledge, under which rollers were used when heavy masses had to

be drawn. Rollers being in demand, and heavy ones being difficult to handle, it is likely that long ones were cut up to make small ones, and the desirability of fixing these would then become felt. Precisely how this was done we do not know, said the author, but conjecture suggests that the middle may have been grooved out to permit of a staple or pegs. on the sledge engaging with the .groove and preventing the roller running along or sideways. This groove may have come to extend the whole width of the sledge, and a natural sequence would be to build this form up out of three parts—two disc-wheels and one axle, the axle being prevented by pegs from rolling away underneath the cart.

According to researches, quoted by Mr. Heathcote, :solid wheels were used by the less-civilized nations of Asia Minor, and on the farm-carts of classic times. Virgil refers to solid wheels built up of three planks held together by an iron hoop, and this form is said to be still in use in Southern Italy and to make a loud creaking noise as it turns. Some of the old Chinese pictures show solid wheels with holes cut out, possibly for lightness, but more probably to admit a pole for skidding the wheel on a decline. This is an ancient method of braking, from which has arisen the phrase, "to put one's spoke into another man's wheel."

Splitting must have been a serious cause of trouble in ancient disc-wheels. Some that are still extant, dating from 1550 B.C., show bad splits and leathern thongs binding the parts together. Segments of treetrunks would necessarily have a limited diameter, and though the large ones would prove better runners on rough roads they would be more likely to split. This may have led to planks' being nailed together, some crosswise, and the survival of the fittest would account for their persistence. From this to radial planks cut parallel to the grain is not a long step, and from radial planks to spokes is a natural sequence. The author then explained the wheel's relation to religion, and reminded his audience of the early Indians' veneration for wheels. He then proceeded to describe some early examples of the wheelmakers' art, and in this connection the following extract from his paper will be read with interest :—

Materials Used in Ancient Wheels.

" The early Egyptian carriage-wheels were made of wood, and some of these are still in existence. Their sculptures show their methods of bending the felloes and rims, spoke-making and wheel-building. The spokes were shaved to make them round and smooth. The Egyptians knew how to produce iron as far back as 3733 B.C., but it was among the Assyrians that this metal was most freely used for the production of tools, weapons, and ornaments, and the Egyptians probably learned many of the uses of iron from them.

" According to Holy Writ, the wheels of Solomon's laver carriages (about 1000 e.c.) were bronze. We read : —1 Their axle-trees and their naves and their

felloes and their spokes were all molten.' At the time of Judah (about 1410 B.C.) we read of the dwellers in the valleys of Palestine having chariots of iron. This probably refers to forged iron ; castiron was probably not known till after the time of Homer (about 900 n.e.), The first Grecian wheels were made of oak. The later Grecian wheels were made entirely of bronze. " Of early British wheels I have no illustrations, but Ciiesar found our ancestors possessed of warchariots which they managed with great skill, implying a long previous acquaintance with the use and manufacture of wheels."

Ancient Wheels—General Considerations.

Before leaving the subject of ancient wheels, Mr. Hea,thcote thought it advisable to consider their main features from one or two present-day points of viewe.g., strength, serviceability, and appearance. He stated that in those times torque would only be applied to a wheel in its plane when occasion arose to put the shoulder to the wheel. They were not built to transmit torque, so when the Egyptian wheels sank in the sand of the Red Sea they gave trouble. The same must have happened in many other cases. Every time a car or chariot curved to the right or left a thrust on the rim would be developed perpendicular to the plane of the wheel, its magnitude depending on the weight, speed, and flexibility of the car, the radius of the curve and the character of the ground. The tendency of this would be to break the spokes near the nave. In overcoming this there were two paths open to the designer : one was to dish the wheel, the other to strengthen the rim ; the former is the modern way, the latter was the method adopted by the ancients. The Greeks provided strength to resist side-thrusts by sometimes employing spokes wider near the nave and with their flat side parallel to the axle. This was also the method employed for building some of the London General Omnibus Company's wheels which came under the author's notice a few years ago.

Modern Wheels.

The Suspension WIted.—Mr. Heathcote then passed on to the next stage in wheel development, which dates from the use of bicycles. During the intervening gap of about 2,500 years the only changes of any importance were the dishing of wheels to resist lateral stresses due to ruts and rounding corners, and arranging the spokes on two cones instead of one. The latter arrangement was employed as early as 1828, and is still used at Woolwich Arsenal in building ambulance-wagon wheels. Strange though it may appear, wheels were not used generally for facilitating transit in Britain, except for chariots, until comparatively recent times. The very first carriage was made for Queen Elizabeth in 1568 ; the first that plied for hire in London were in 1625, and the first stage-coaches in 1659. Broadly speaking, all these early wheels were compression wheels with radial spokes. The introduction of the suspension wheel for the bicycle marked a great advance in the shock-absorbing powers of wheels. The first bicycle wheels were compression wheels, and had wooden spokes and rims with iron tires. The wheels were just ordinary light carriage wheels. Later bicycle wheels had radial-wire .spokes which, being in tension, kept the rim in position. It is a common, though not unnatural error, said the author, to suppose that the spokes of a modern bicycle wheel are sometimes in compression. As a matter of fact, they are always in

tension, even those between the hub and the ground, when a heavy rider is in the saddle.

The Tangent-spoke Wheel.---The tangent-spoke wheel, in which the spokes are tangent to a circle having its centre at the axle and are not normal to the rim, was then dealt with by the reader, who thought that this type of wheel probably owes its origin to the curved arms used in driving pulleys and flywheels for transmitting considerable torque. Both ancient and modern radial-spoke wheels, he stated, are capable of transmitting a certain amount of torque, but the amount is limited, and depends not only on the bending strength of the spoke, but on the rigidity of its attachment to both rim and hub. Since no material has an infinite elasticity, it follows that however thick the spokes may be there must be .a certain amount of twist of the hub (in the plane of the wheel) relatively to the rim, or no drive can be transmitted. When the torque is considerable—as in a motorcar rear wheel, the actual twist sooner or later rises above that. corresponding to the elastie limit at some or all of the spoke attachments, and this leads to the gradual loss of rigidity and to creaking, and, in some cases, even to charring of the wood, owing to rubbing. In a radial-spoke bicycle wheel subjected to a torque in its plane, the hub must rotate relatively to the rim until the spokes are ta.ngent to a small circle. Radial wheels have to be subjected to great radial tension or compression in order to impart the necessary torque rigidity. In tangent, wheels the necessary torque rigidity can he attained without imparting excessive radial rigidity. As a result of this the tangent suspension wheel can be made capable of absorbing shock, said Mr. Heathcote, and he added that wheel-building is the counterpart of tire-inflation, and the art produces its best when sufficient tension to produce torque rigidity is

combined with conditions that develop in the wheel a maximum cushioning effect. Such a wheel, by cooperating in the duties of the tire, lengthens the lire's life and lessens its liability te wear, cuts and punctures. To obtain maximum cushioning from a wheel of this type, moderate spoke tension needs to be combined with a flexible and resilient rim and thin spokes. A large number of experiments and tests were then described, and these went to show the great advantage of a wheel's having a flexible rim—an advantage possessed only by the tangent-spoke type of wire wheel. In nearly every test mentioned, the deflection of a wood wheel for the same pull is greater than on a wire wheel, and in every case the wood wheel sustained permanent damage at a lower pull than in the wire wheel. Having then advanced arguments to support his claim that Rudge-Whitworth wire wheels are greatly superior to all other forms, Mr. Heathcote outlined the various tests to which material and detail parts of his company's wheels are subjected in the works, both before and during the course of construction. A number of other types of wheels were lightly treated by the Author, whose paper was followed

by a. brief but interesting discussion. The Hon. Richard Clere Parsons, M.A., Vice-President of the Society, who occupied the chair, made a few practical remarks on the need for side stability of wheels in both directions ; the inside edge of a wheel is just as likely violently to come into contact with a projecting tram-rail as the outside edge to strike the kerb when side-slip occurs. Mr. Parsons has evidently observed the 'damaging effects of projecting, or even well-kept tram-rails—the enemies (or are they the friends-) of wheel builders. Certainly they are the enemies of dirigible vehicles, whether drawn by animals or propelled by mechanical power.

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Organisations: Royal Society of Arts
Locations: London

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