Fig. 1501.
The feed obviously occurs once for each cutting stroke of the tool and for the vertical motion of the tool, or when the tool is operated by the hand feed-screw handle in [Fig. 1496], the handle motion, and therefore the feed should occur at the end of the back stroke and before the tool again meets the work, so as to prevent the cutting edge of the tool from scraping against the work during its back traverse.
In this connection it may be remarked that by setting the apron swivel over, as in [Fig. 1498], the tool is relieved from rubbing on the back stroke for two reasons, the first having been already explained, and the second being that to whatever amount the tool may spring, bend, or deflect during the cutting stroke (from the pressure of the cut), it will dip into the work surface and cut deeper; hence on the back stroke it will naturally clear the surface, providing that the next cut is not put on until the tool has passed back and is clear of the work.
Referring now to the automatic feed of the sliding table w, in [Fig. 1496], the principle of its construction may be explained with reference to [Fig. 1501], which may be taken to represent a class of such feeding mechanisms. a is a wheel corresponding to the wheel marked m in [Fig. 1496], or, it may be an independent wheel in gear with the feed wheel. On the same shaft as a is pivoted an arm b having a slot s at one end to receive a pin to which the feed rod e may connect. f is a disk rotated from the driving mechanism of the shaping machine, and having a T-shaped slot g g, in which is secured a pin to actuate the rod e. As f rotates e is vibrated to and fro and the catch c on one stroke falls into the notches or teeth in a and causes it to partly rotate, while on the return stroke of e it lifts over the teeth, leaving a stationary.
The amount of motion of b, and therefore the quantity of the feed, may be regulated at either end of e; as, for example, the farther the pin from the centre of g the longer the stroke of e, or the nearer the pin in s is to the centre of b the longer the stroke, but usually this provision is made at one end only of e.
To stop the feed motion from actuating, the catch c may be lifted to stand vertically, as shown in dotted lines in position 2, and to actuate the feed traverse in an opposite direction, c may be swung over so as to occupy the position marked 3, and to prevent it moving out of either position in which it may be set a small spring is usually employed.
Fig. 1502.