Fig. 1573.
The form of cross bar usually employed in the United States is represented in [Fig. 1573], and it is clear that the pressure of the cut is in the direction of the arrow c, and that the fulcrum off which the strain will act on the cross bar is at its lowest point d, tending to pull the top of the saddle or slider in the direction of arrow e, which is directly resisted by the vertical face of the gib, while the horizontal face f of the gib directly resists the tendency of the saddle to fall vertically, and, therefore, the amount of looseness that may occur by reason of the wear cannot exceed the amount of metal lost by the wear, which may be taken up as far as possible by means of the screws a and b, which thread through the saddle and abut against the gib. The gib is adjusted by these screws to fit to the least worn and therefore, the tightest part of the cross bar slideway, and the saddle is more loosely held at other parts of the cross bar in proportion as its slideway is worn.
Fig. 1574.
In this construction the faces of the saddle are brought to bear over the whole area of the slideways surface of the cross bar, because the bevel at g brings the two faces at m into contact, and the set-screw b brings the faces in together. Instead of the screws a and b having slotted heads for a screw driver, however, it is preferable to provide square-headed screws, having check nuts, as in [Fig. 1574], so that after the adjustment is made the parts may be firmly locked by the check nuts, and there will be no danger of the adjustment altering.
Fig. 1575.