Purpose
The coupled driving wheels on steam locomotives (often simply called "drivers") were held in a straight line by the locomotive's frame. The flanges of the drivers were spaced a bit closer than the rail gauge, and they could still fit between the rails when tracking through a mild curve. At some degree of curvature, though, the flanges on the center driver would begin to bind in the curve. The farther apart were the front and rear drivers, the less track curvature the locomotive could negotiate. One solution was to make the center driver(s) without flanges on the tires. The other solution was to allow at least one of the axles (often the front driver) to move lateral to the frame, and such designs incorporated various devices to permit this motion.
Read more about this topic: Lateral Motion Device
Famous quotes containing the word purpose:
“Along the journey we commonly forget its goal. Almost every vocation is chosen and entered upon as a means to a purpose but is ultimately continued as a final purpose in itself. Forgetting our objectives is the most frequent stupidity in which we indulge ourselves.”
—Friedrich Nietzsche (1844–1900)
“To every thing there is a season, and a time to every purpose under the heaven:
A time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted;”
—Bible: Hebrew Ecclesiastes (l. III, 1–2)
“It is my purpose to disclose the mystery at once, and to ask you to look for your interest,—should you choose to go on with my chronicle,—simply in the conduct of my persons, during this disclosure to others.”
—Anthony Trollope (1815–1882)