Fig. 2407.
Fig. 2408.
It has thus far been supposed that the joint faces of the brasses are made to come brass and brass, that is to say, butt close together from the key pressure, when the brass bores properly fit the journal. Suppose, however, that the joint of the brass is left open as in [Fig. 2407], and in that case a strip of metal f, whose diameter equals that of the journal, may be inserted between the brasses as shown, and at its centre should be provided a small centre-punch mark, denoting the centre of the bore. A piece of this kind should be inserted in the brasses at each end of the rod and placed in the middle of the length of the bore, the centre-punch marks being to apply the trammels to. Or if the rod was made of correct length when new, and the bore of the brasses, therefore, requires to stand central in space f, [Fig. 2403], then the pieces f, [Fig. 2407], may be dispensed with by marking a line b, [Fig. 2408], central to space f, [Fig. 2403]. Then put the strap on the rod (with the brasses, gib, and key in place), and pull the strap back to hold the key up to its proper height.
Fig. 2409.
The two brasses should then be placed as far apart as possible in the strap, each bedding fairly against its back or crown. Then, using the joint face of the back brass as a straight-edge or guide, a line should be marked on the side face of the strap, this line representing the position of that face when the brass is bedded fairly home, and being shown in [Fig. 2408] at a. This brass should then be moved forward until the bore of the pair of brasses at d, [Fig. 2408], measures equal to the diameter of the journal (of the crank pin or of the cross-head pin as the case may be) and a second line b, also coincident with the joint face of the brass, should be marked upon the strap, and the strap will then have marked on it the two lines shown in [Fig. 2409], in which it is shown removed from the rod; the distance apart of these two lines will be the thickness of the two liners combined, hence half this thickness will be the thickness necessary for each liner. Suppose, however, that it is not known whether the rod has been correctly made, and therefore it be unknown whether, in order to have the rod of the correct length, the brass bore should stand in the centre of the space or not.