Fig. 1515.
The sliding jaw will in this case be against face c, and if that face is out of true enough to cant the work so that a will not bed fair, then a narrow parallel piece may be inserted between the sliding jaw and the work, which will cause a to bed fair. The third face should be face c, in which case face a will rest on one surface and face b will be against the fixed jaw, and there will be two surfaces to guide the work true while c is being trued. In this case also, however, it is better to use a parallel piece p, [Fig. 1515], between the work and the sliding jaw, so as to insure that the work shall bed fair against the fixed jaw; and if necessary to bring up the top surface above the jaws, a second parallel piece p′ should be used.
Suppose now that we have a connecting rod key to shape, and it is to be considered whether the faces or the edges shall be shaped first. Now if the side faces are out of parallel it will take more filing to correct them than it will to correct the same degree of error in the edges; hence it is obviously desirable to proceed with a view to make all surfaces true, but more especially the side faces. As the set of the key while shaping these faces is most influenced by the manner in which the fixed jaw surface meets the work, and as an edge will be the surface to meet the fixed jaw faces when the side faces are shaped, it will be best to dress one edge first, setting the key or keys, as the case may be, as was shown in [Fig. 1510], so as to cut them with the tool operating lengthways of the key; one edge being finished, then one face of each key must be shaped, the key being set for this purpose with the surfaced edge against the fixed jaw. As the width of the key is taper, either a chuck with a taper attachment that will permit the sliding jaw to conform itself to the taper of the key must be used (vices having this construction being specially made for taper work as will be shown hereafter), or else the key must be held as in [Fig. 1516], in which k represents the key with its trued edge against the fixed jaw, at p is a piece put in to compensate for the taper of the key, and to cause the other edge to bed firmly and fairly against the fixed jaw.
Fig. 1516.
The first side face being trued, it should be placed against the fixed jaw while the other edge is shaped. For the remaining side face we shall then be able to set the key with a trued edge against the fixed jaw, and a true face resting upon a parallel piece, while the other edge will be true for the piece p, [Fig. 1516], to press against, and all the elements will be in favor of setting the key so that the sides will be parallel one to the other, and the edges square with the faces.
In putting in the piece p, [Fig. 1516], the key should be gripped so lightly that it will about bear its own weight; piece p may then be pushed firmly in with the fingers, and the vice tightened up.