Fig. 1631.
Another excellent method is to balance the bed on three points, two at one end and one at the other, and to then pack it up equally at all four corners.
To test if the surface of a piece of such work has been planed straight, the following plan may be pursued:—
Fig. 1632.
Suppose that surface e, [Fig. 1632], is to be tested, it having been planed in the position it occupies in the figure, and the casting may be turned over so that face e stands vertical, as in [Fig. 1632], and a tool may be put in the tool post of the planer, the bed being adjusted on the planer table so that the tool point will just touch the surface at each end of the bed. The planer table is then run so that the tool point may be tried with the middle of the bed length, when, if the face e is true, it will just meet the tool point at the middle of its length as well as at the ends.
In the planing of the V-guides and guideways of a bed for a machine tool, such as, for example, a planer bed and table, the greatest of care is necessary, the process being as follows:—
Beginning with the bed it has been shown in [Fig. 1601] that the sides of the guideways must all be of the same height as well as at the same angle, and an excellent method of testing this point is as follows:—