All the dimensions are to be taken from the detail drawings (b), (c), (d), and (e), but the details need not be drawn separately. The brass bush is shown at (d) by half elevation, half vertical section, half plan, and half horizontal section. The draught or clearance is 7-16ths of an inch.
Fig. 41.
Box End.—At (a), fig. 42, is shown what is known as a box end for a connecting rod. The part which corresponds to the loose strap in the last example is here forged in one piece with the connecting rod. In this form the brass bush is provided with a flange all round on one side, but on the opposite side the flange is omitted except at one end; this is to allow of the bush being placed within the end of the rod. The construction of the bush will be understood by reference to the sketch shown at (b). The bush is in two parts, which are pressed tightly together by means of a cotter. This cotter is prevented from slackening back by two set screws. Each set screw is cut off square at the point, and presses on the flat bottom of a very shallow groove cut on the side of the cotter.
The top, bottom, and ends of this box end are turned in the lathe at the same time as the rod itself; this accounts for the curved sections of these parts.
It is clear from the construction of a box end that it is only suitable for an overhung crank.
Exercise 42: Locomotive Connecting Rod.—In fig. 42 is shown a connecting rod for an outside cylinder locomotive. (a) is the crank-pin end, and (c) the cross-head end. The end (a) has just been described under the head 'box end.' We may just add that in this particular example the brass bush is lined with white metal as shown, and that the construction of the oil-box is the same as that on the coupling rod end shown in fig. 44. The end (c) is forked, and through the prongs of the fork passes the cross-head pin, of which a separate dimensioned drawing is shown at (d). Observe that the tapered parts A and B of this pin are parts of the same cone. The rotation of the pin is prevented by a small key as shown. The cross-head pin need not be drawn separately, and the isometric projection of the bush at (b) may be omitted, but all the other views shown are to be drawn to a scale of 6 inches to a foot.
