The above remarks may be qualified by stating that some of the largest manufacturers have introduced machinery, generally, into the departments in which it is applicable, and more particularly in the wheelwrights’ department. Some years since Messrs. Holmes, of Derby, had mechanical appliances worked by steam power for the following purposes:—Cutting tenons on the spokes, squaring the ends of the felloes, also regulating their length according to the size of wheel required; a narrow upright saw for cutting curved timber; machine for cutting felloes of the required size and curve; machine for boring felloes for the ends of spokes, and many other appliances for lightening hand-labour and insuring greater accuracy in the manufacture. But workshops filled up in this way are not yet the rule, though their number is increasing, and so are the inventions for application of mechanical power to the various processes.
Fig. 19.
It seems rather paradoxical to state that the dished or conical wheel is the strongest. But the fact is, its strength arises from the solid hoop-tyre; with a strake tyre the upright wheel would be the strongest. When running, the great lateral strain on the wheel is from the outside. Consequently, if the wheel be dished in an opposite direction, the thrust will be in the direction of the greatest resistance. The spokes cannot yield, because in yielding they would increase the area of the circle, and this the tyre will not permit. Upon the same principle in carpentry, which constitutes the curved or cambered beam the strongest, the dished wheel is stronger than the straight one.
Here is one very important item which must not be overlooked in the wheelwright department, and that is, the size of the axle-box. The axle-box is a lining of cast iron, on which the axle-arm takes its bearing. Two forms of these are given in Figs. [18] and [19].
Fig. 20.
[Fig. 20] shows an improved form of stock. It will be seen it is to be applied to straight wheels, and requires no further description beyond noting that the stock is not weakened so much as in the ordinary way by mortising, an iron band, A, circumscribing the nave and forming a hold for the spokes.
Wheels should be made with a sufficient number of spokes to properly divide the space at the felloes, and afford sufficient support to prevent sinking in between the spokes, and at the same time avoid too many to weaken the stock. The less the number of spokes, the stronger the hub and the weaker the felloe. Judgment should be used in dividing the difference, so as to make each part of the wheel strong in proportion.