ANGULARITY OF CONNECTING ROD.
In following out the relative motion of the piston and crank, we discover a disturbing factor in what is called the angularity of the connecting rod, which has a curiously distorting effect on the harmony of the motion. When the piston stands exactly in the mid-travel point, the true length of the main rod will be measured from the center of the wrist-pin to the center of the driving-axle. If a tram of this length be extended between these points, this will be found correct, as every machinist accustomed to working on rods knows. Now, if the back end of the tram should be raised or lowered towards the points where the center of the crank-pin must be when the crank stands on the top or bottom quarter, it will be found that the tram point will not reach the crank-pin center, but will fall short a distance in proportion to the length of the main rod. The dotted lines a′ and b′ in [Fig. 11] show how far a rod 7½ times the length of the crank falls short. A shorter rod will magnify this obliquity, while a longer rod will reduce it.
Fig. 11.