Again, the keyways in the strap will not be set out of true with those in the rod, as they are apt to be when upsetting is resorted to, nor will the strap be scaled; hence the side faces will require but little filing.
Furthermore the step may be located so as to come against the rod end when the wear has let the key down, and this will prevent the strap from passing too far upon the rod, and, therefore, tend to prevent the rod length from being improperly altered from errors in the thickness of the liners placed behind the brasses to take up the wear.
Fitting up Connecting Rods.—The method of fitting up a connecting rod depends entirely upon its size. Very small rods to be made in numbers are usually got out by means of special devices which leave the fitter but little to do; indeed, sometimes the machine work is so accurately and finely fitted and finished as to finish the rod without the aid of the vice hand, save to put it into its place upon the engine or machine. As, however, the dimensions of the rod increase, this method of manipulation is in practice departed from, and the filing, fitting, and adjusting operations increase. In any event, however, the principles to be observed in the manipulation are the same, because the points to be observed in the fitting by hand work must be accomplished by the machine if the rods are to be finished by machine work.
Fig. 2360.
Let [Fig. 2360] represent a connecting rod; a representing the centre line in the side, and f the centre line in the edge view, and it is obvious that the axial lines, b and c, of the brass bores must stand at a right angle to line f, and be parallel to each other, because the journals on which they fit will do so. Furthermore, the faces of the brasses, as e, must stand their proper distance from the centre line f, this distance being at each end respectively half the whole width d, and the faces e must be in the same plane whatever their widths may be. The centre lines a and f are imaginary lines not worked to (except it be in marking or lining the rod out for the planing operations); but the method employed to fit up the rod must be such as will make all parts true to those lines if they were tested by them.
The process of fitting up a connecting rod may be tersely stated as follows: 1st, the rod is planed; 2nd, the straps are planed; 3rd, the straps are fitted to the rods; 4th, the straps are drilled and bolted to the rod; 5th, the keyways are cut, and the keys and gibs fitted; 6th, the side faces of the rod ends are again planed with the straps on; 7th, the brasses are fitted and the rods marked off for length and the brasses bored; and, 8th, the file finishing and polishing done.
