INFLUENCE OF HALF-ROUND BRASSES.
Driving-boxes fitted with a half-round brass have a tendency to close at the bottom. This tendency is continuous, and becomes most marked as the brass wears down, relieving the box of the strain put upon it by the tight-fitting brass. With a properly fitted brass, and a collar put up in good shape, the box can not close much: still, there will be enough looseness to cause a slight pounding. During the first few days’ service of a locomotive after new driving-brasses of this shape are put in, the compression on the brass, resulting from the weight of the engine, tends to close the bottom of the box, and permits the box to rock. This evil may be, to some extent, prevented by fitting the wedges slightly closer at the bottom. This closing of the box at the bottom is not only an evil and annoyance in itself by causing pounding, but is a further source of trouble by hastening the forming of a shoulder on the top of the wedge. The tendency at all times is for the axle-box to wear a shoulder at the top and bottom of its travel, even when the box retains its proper shape; but, when it is distorted by closing at the bottom, the rubbing surfaces are put out of the true plane, and wear takes place much more rapidly. While the springs retain their position, and impart to the axle-box a fixed range of motion, no serious effect is felt from the worn wedges. But when the locomotive is passing over rough frogs or bad rail-joints, where the motion of the spring is increased, the frame pounds down upon the box, which for a moment becomes fastened in the narrow space between the shoulders of the wedges; and an effort is needed for the box to relieve itself, and allow the spring to resume its motion. This causes the engine to ride hard in some instances, where the condition of the track makes the box catch frequently. Sometimes the box will be unable to relieve itself without assistance, and much loss of time and annoyance result when the wedge has to be pulled down to relieve the box.
The forming of the shoulder on top and bottom of the wedge may be anticipated and prevented by planing the part where the ridges form, leaving a face just the length of the box plus the space covered by the motion of the springs. Not only does this aid in preventing the box from forming a shoulder, but it also reduces the first cost of fitting the wedges by reducing the surface to be squared and finished true.