Fig. 1576.
The wear between the slider and the raised slideways s is taken up by gibs and screws corresponding to those at a and c in the [Fig. 1575], and concerning these gibs and screws J. Richards has pointed out that two methods may be employed in their construction, these two methods being illustrated in [Figs. 1575] and [1576], which are taken from “Engineering.”
In [Fig. 1575] the end s of the adjustment screw a is plain, and is let into the gib c abutting against a flat seat, and as a result while the screw pressure forces the gib c against the bevelled edge of the slideway it does not act to draw the surfaces together at m m as it should do. This may be remedied by making the point of the screw of such a cone that it will bed fair against gib c, without passing into a recess, the construction being as in [Fig. 1576], in which case the screw point forces the gib flat against the bevelled face and there is no tendency for the gib to pass down into the corner e, [Fig. 1575], while the pressure on the screw point acts to force the slide a down upon the slideway, thus giving contact at m m.
Fig. 1577.
The bearing area of such screw points is, however, so small that the pressure due to the tool cut is liable to cause the screw to indent the gib and thus destroy the adjustment, and on this account a wedge such as shown in [Fig. 1577] is preferable, being operated endwise to take up the wear by means of a screw passing through a lug at the outer or exposed end of the wedge.
The corners at i, [Figs. 1575] and [1576], are sometimes planed out to the dotted lines, but this does not increase the bearing area between the gib c and the slide, while it obviously weakens the slider and renders it more liable to spring under heavy tool cuts.