Fig. 2385.
Fig. 2386.
Fig. 2387.
The ways for the brasses should be filed square with the outside faces, as shown in [Fig. 2385], in which s is a T-square; but if one jaw is wider than the other, as sometimes occurs, it will not matter, providing that, with the square applied, resting against the side and the face of the ways on the narrow jaw, the ways of the other jaw are equidistant from the square blade, as would be the case; for example, if the width of the ways of the jaw j extended to the dotted lines at k, l, because the line p would still form the centre line of both jaws, standing at a right angle to the side faces of the fork end, and parallel to the bore of the brasses at the butt end. Before filing up the side faces at the butt end, the strap should be fitted on and keyed up, so that its side faces may be filed up with those on the rod. To test the truth of the side faces at the butt end, a straight-edge should be applied, as at s and s′′, [Fig. 2386], being pressed firmly to the side faces at the butt b, the fork faces being measured from the edge of the straight-edge at that end, and also with straight-edges, as in [Fig. 2384]. The brasses, after being fitted into the ways of the jaws, should have their joint faces squared, as in [Fig. 2387], the top of each jaw being shown broken away, so as to fully expose the brasses. s is a square held firmly against the side face of a jaw, the brasses having their joint faces true with the square blade, and true also when tested with a square, applied as in [Fig. 2388], in which b is the brass and s the square. The brasses at the other end should be filed true to the side faces of the strap in a similar manner, and, the fitting being completed, it simply remains to mark off the brasses for boring. The joint faces of the brasses should form the centre of their respective bores; hence, all that is necessary, is to insure that the brasses be of equal thickness, top and bottom, and this may be accomplished as follows: Mark across each face a line even with the ways of the brass, as shown in [Fig. 2389], at a, c, and carry these lines around the side face, as shown in the figure at b, d. Place the brasses in the strap, put in a piece of wood whereon the compasses may be rested, as shown in [Fig. 2390], which represents one jaw, and mark on this piece of wood a line even with the joint faces of the brasses, and on this line a centre-punch dot equidistant between the lines b, d. From this dot, as a centre, strike the circle shown, and define it by centre-punch dots, and if the lathe-hand chucks the brasses true to the ways that fit the rod jaws, and to the dotted circle, the bores will stand true in every respect.
