Fig. 2347.
The simplest form of strap-ended connecting rod is that shown in [Fig. 2345]; s is the strap, secured to the rod end by the key d and gib c. a is the top, and b the bottom, or crown brass, and e the set-screw for securing the key in its place. [When the rod ends are forged in separate pieces, to be afterwards welded to the stem of the rod after the strap brasses are fitted up (which is done for convenience in handling them while fitting them up), they are termed stub ends.] This form of rod affords great facility for connection with the journals as the strap is easily removed. As the strap, however, is only secured to the rod by the gib and key, and as these have a small amount of area on the sides, it is not unusual to employ two gibs and one key, as in [Fig. 2346], which holds the strap more securely, and more effectually prevents its movement sideways upon the rod end. In rods in which gibs and keys alone are used to hold the strap to the rod, the strap moves along the rod as the key passes farther through the strap, and the fit of the strap to the rod must be easy enough to permit of this motion; hence it cannot be locked to the rod. This, however, may be done by the employment of a bolt as well as a gib and key, as is shown in [Fig. 2347]. The edge of the gib here abuts against the back of the top brass, or key brass, as it is sometimes termed, which is objectionable, inasmuch as that it is apt to indent the brass, as shown in [Fig. 2348] at b. This causes the bore to close at a, and causes the journal to heat, while it makes the brass fit loosely between the jaws of the strap, because it stretches the metal at the back of the brass, which has the same effect as pening it with the hammer.
Fig. 2348.
Fig. 2349.
In [Fig. 2349] is shown an end of a connecting rod, such as is employed on American locomotives, the use of a gib being dispensed with, and the strap being held by two bolts. To prevent the edge of the key from imbedding in the brass, a piece of hardened steel is sometimes placed between the key and the brass, as shown in the figure.