Fig. 1558.
[Fig. 1558] represents a planer by David W. Pond, of Worcester, Massachusetts, in which the rod x is connected direct from s to a pivoted piece y in which is a cam-shaped slot through which pass pins from the belt-moving arms u and w. The shape of the slot in y is such as to move the belt-moving arms one in advance of the other, as described with reference to [Fig. 1566].
The feed motions are here operated by a disk c, which is actuated one-half a revolution when the work table is reversed. This disk is provided on its face with a slide-way in which is a sliding block that may be moved to or from the centre of c by the screw shown, thus varying at will the amount of stroke imparted to the rod which moves the rack by means of which the feed is actuated through the medium of the gear-wheels at f. The handle g is for operating the feed screw when the self-acting feed is thrown out of operation, which is done by means of a catch corresponding in its action to the catch shown in [Fig. 1501]. s and s′ are in one piece, s′ being to move the two driving belts on to the loose pulleys so as to stop the work table from traversing.
The size of a planer is designated from the size of work it will plane, and this is determined by the greatest height the tool can be raised above the planer table, the width between the stanchions, and the length of table motion that can be utilized while the tool is cutting; which length is less than the full length of table stroke, because in the first place it is undesirable that the rack should pass so far over the driving wheel or pinion that any of the teeth disengage, and, furthermore, a certain amount of table motion is necessary to reverse after the work has passed the tool at the end of each stroke.
Fig. 1559.
[Fig. 1559] represents a method employed in some English planing machines to drive the work table and to give it a quick return motion. In this design but one belt is used, being shifted from pulley a, which operates the table for the cutting stroke, to pulley j, which actuates the table for the return stroke. The middle pulley k is loose upon shaft b, as is also pulley j, which is in one piece with pinion j′. Motion from a is conveyed through shaft b and through gear c, d, e to f, and is reduced by reason of the difference in diameter between d and e and between f and g. Motion for the quick return passes from j direct to f without being reduced by gears d, e, hence the difference between the cutting speed and the speed of the return stroke is proportionate to the relative diameters or numbers of teeth in d and e, and as e contains 12 and d 20 teeth, it follows that the return is 8⁄12 quicker than the cutting stroke.