Thus for taper work the work-holding frame may be set out of parallel with the base of the chuck to an amount answering to the required amount of taper, being raised or lowered (as may be most convenient) at one end by means of the gears m, of which there is one on each side meshing into the segmental rack shown, the work-holding frame being secured in its adjusted position by means of a set bolt.
To set the work-holding frame parallel for parallel planing, a steady pin is employed, the frame being parallel to the base when that pin is home in its place.
The construction of the chuck is solid, and the various adjustments may be quickly and readily made, giving to it a range of capacity and usefulness that are not possessed by the ordinary forms of planer chucks.
Planing Machine Beds.—In long castings such as lathe or planer beds, the greatest care is required in setting the work upon the planer table, because the work will twist and bend of its own weight, and may have considerable deflection and twist upon it notwithstanding that it appears to bed fair upon the table. To avoid this it is necessary to know that the casting is supported with equal pressure at each point of support. In all such work the surface that is to rest upon the foundation or legs should be planed first.
Thus supposing the casting in [Fig. 1630] to represent a lathe shears, the surfaces f whereon the lathe legs are to be bolted should be planed first, the method of chucking being as follows:—
Fig. 1630.
The bed is balanced by two wedges a, in [Fig. 1630], one being placed at each end of the bed, and the position of the wedges being adjusted so that it lies level. A line coincident with the face of the bed (as face d) is then drawn across the upper face of each wedge. Wedges (as b, c,) are then put in on each side of the bed until they each just meet the bed, and a line coincident with the bed surface is drawn across their upper surfaces. Wedge b is then driven in until it relieves a of the weight of the bed, and a second line is drawn across its upper face. It is then withdrawn to the first line, and the wedge on the opposite side of the bed is driven in until a is relieved of the weight, when a second line is drawn on this wedge’s face. The wedges at the other end (as c) are then similarly driven in and withdrawn, being also marked with two lines, and then the four wedges (b, c, and the two corresponding ones on the opposite side of the bed) are withdrawn, having upon their surfaces two lines each (as a, b, in [Fig. 1631]). Midway between these two lines a third (as c) is drawn, and all four wedges are then driven in until line c is coincident with the bed surface, when it may be assumed that the bed is supported equally at all the four points. When the bed is turned over, surfaces f may lie on the table surface without any packing whatever, as they will be true.