Fig. 3245.
Fig. 3246.
[Fig. 3245] represents a single and [Fig. 3246] a double riveted butt joint, so called because the ends of the boiler plate abut together. The plates on each side of joint are called butt straps.
The advantages of the butt joint are, first, that the boiler shell is kept more truly cylindrical, and the joint is not liable to bend as it does in the lap joints, in the attempt of the boiler (when under pressure) to assume the form of a true circle, and second that the rivets are placed in double shear. That is to say, if in a lap joint the rivet was to shear between the plates, the joint would come apart, whereas, in a butt joint, the rivet must shear on each side of the plate, and therefore in two places.
Fig. 3247.
[Fig. 3247] represents a form of joint much used in locomotive practice in the United States. It is a lap joint, with a covering plate on the inside of the joint; rivets e and f are in single and rivets d in double shear.