This direction is periodically reversed as follows:—The pulley p is driven by a crossed belt, while pulley p′ is driven by an open or uncrossed one, hence the direction of revolution of the driving pulley p′′ will be in one direction if the belt is moved from p to p′′, and in the other if the belt is moved from p′ to p′′. Mechanism is provided whereby first one and then the other of these belts is moved so as to pass over upon p′′ and drive it, the construction being as follows:—
To the edge of the work table there is fixed a stop r, which as the table traverses to the right meets and moves a lever arm s, which through the medium of a second lever operates the rod x, which operates a lever u, which has a slot through which one of the driving belts passes. The lever u operates a second lever w on the other side of the pulleys, and this lever also has a slot through which the other driving belt passes.
When the stop r moves the lever arm s levers u and w therefore move their respective belts, one moving from the tight pulley p′′ to a loose one as p, and the other moving its belt from the loose pulley as p′ to the tight one p′′, and as the directions of belt motions are opposite the direction of revolution of p′′ is reversed by the change of belt operating it. There are two of the stops r, one on each side of the lever s, hence one of these stops moves the lever s from left to right and the other from right to left.
Suppose, then, that the table is moving from right to left, which is its cutting stroke, and the driving belt will be on the pulley p′′ while the other belt will be on pulley p. Then as the stop r moves s and operates x the arm u will move its belt from p′′ to p′, and arm w will move its belt from p to p′′, reversing the direction of motion of p′′, and therefore causing the table t to move from left to right, which it will continue to do until the other stop corresponding to r meets s and moves it from right to left, when the belts will be shifted back again. The stroke of the table, therefore, is determined by the distance apart of the stops r, and these may be adjusted as follows:—
They are carried by bolts whose heads fit in a dovetail groove z provided along the edge of the table, and by loosening a set screw may therefore be moved to any required location along the bed.
To give the table a quick return so that less time may be occupied for the non-cutting stroke, all that is necessary is to make the countershaft pulley that operates during the back traverse of larger diameter than that which drives during the cutting traverse of the table.
In order that one belt may have passed completely off the driving pulley p′′ before the other moves on it the lever motions of u and w are so arranged that when the belt is moving from p′′ to p lever u moves in advance of lever w, while when the other belt is being moved from p′′ to p′ lever w moves in advance of lever u.
To enable the work table to remain at rest, one driving belt must be upon p and the other upon p′, which is the case when the lever arm s is in mid position, and to enable it to be moved to this position it is provided with a handle k forming part of lever s.
To cause the tool to be fed to its cut before it meets the cut and thus prevent it from rubbing against the side of the cut, as was described with reference to [Fig. 1503], the feed takes place when the table motion is reversed from the back or return stroke to the cutting or forward stroke by the following mechanism:—
At a is a rack that is operated simultaneously with s and by the same stop r. This rack operates a pinion b, which rotates the slotted piece c, in which is a block that operates the vertical rod d, which is attached to a segmental rack e, which in turn operates a pinion which may be placed either upon the cross-feed screw j, or upon the rod above it; the latter operates the vertical feed of the tool through mechanism within the head d and not therefore shown in the engraving. Thus the self-acting tool feed may take place vertically or across the work table at will by simply placing the pinion upon the cross-feed screw or upon the feed rod, as the case may be.