Practical Carriage Building
Compiled by M.T. Richardson, Vol.1. 1891
The Dishing of Wheels Part 3
What regulates the amount of dish? To satisfactorily answer this question several particulars must be considered the most important one among which is the nature of the material from which the wheel is constructed. It is safe to say in general terms that the amount of dish depends upon the crushing strength of the material of the wheel. The softer this material is, the more dish is necessary. When a wheel is dished, it is impossible for it to assume the upright form without the material crushing. The length of the spoke must be reduced before it can change from its angular position to a vertical one in the wheel. It must force its extra length either into the hub or the felloe. This is clearly indicated in Fig. 147. The dish must at least be just sufficient to prevent the possibility of the spokes assuming the position of the dotted lines.
The dish then may be said to vary according to the hard¬ness or softness of the material, and the amount of the safe margin adopted by designers. Two other questions may be with propriety considered in this connection. The first of these is, What is the best position of a wagon wheel? In answer, I would say, for reasons made evident in the foregoing, that the lower spoke should be vertical, so far as carrying the load is concerned, and on no account must it deviate far from this position.
In practice good results are obtained by allowing the lower part to spread a little, thus avoiding the possibility of the wheel taking the opposite position, which would be bad. The second of the two questions last referred to is, What kind of an axle arm is most suitable for the work to be per¬formed? This question, of course, presumes a dished wheel, but I have already shown that, all other considerations aside, the opening through the hub should be horizontal when the axle rests upon it. Hence it follows that a taper axle is a necessity, for nothing else can be used under the conditions existing. The taper of the arm depends upon the amount of dish, just as the size depends upon the weight to be carried. In practice, the under line of a taper axle should be some¬what lower at the outer end, in order to prevent too much wear on the outer collars. If a wheel is used which has but very little dish, a parallel axle may be employed, and in such cases it is likely to wear longer than a taper axle, because it has a larger surface area to support the weight resting upon it, and therefore sustains less weight per square inch.— WAWAYANDA