Fig. 1578.
[Fig. 1578] represents a form of cross bar and gib found in many English and in some American planing machines. In this case the strain due to the cut is resisted directly by the vertical face of the top slide of the cross bar, the gib being a triangular piece set up by the screws at a, and the wear is diminished because of the increased wearing surface of the gib due to its lower face being diagonal.
On the other hand, however, this diagonal surface does not directly resist the falling of the saddle from wear, and furthermore in taking up the wear the vertical face of the saddle is relieved from contact with the vertical face of the cross bar, because the screws a when set up move the top of the saddle away from the cross bar, whereas in [Fig. 1573], setting up screw b brings the saddle back upon the vertical face of the cross bar slideway.
Fig. 1579.
