Fig. 1587.
In some planing machines, and notably those made by Sir Joseph Whitworth, a swiveling tool holder is made so that at each end of the stroke the cutting tool makes half a revolution, and may therefore be used to cut during both strokes of the planer table. A device answering this purpose is shown in [Fig. 1587]. The tool-holding box is pivoted upon a pin a, and has attached to it a segment of a circular rack or worm-wheel, operated by a worm upon a shaft having at its upper end the pulley shown, so that by operating this pulley, part of a revolution at the end of each work-table stroke, one or the other of the two tools shown in the tool box, is brought into position to carry the cut along. Thus two tools are placed back to back, and it is obvious that when the tool box is moved to the right, the front tool is brought into position, while when it is moved to the left, the back or right-hand tool is brought into position to cut, the other tool being raised clear of the work.
The objections to either revolving one tool or using two tools so as to cut on both strokes are twofold: first, the tools are difficult to set correctly; and, secondly, the device cannot be used upon vertical faces or those at an angle, or in other words, can only be used upon surfaces that are nearly parallel to the surface of the work table.
Fig. 1588.
