Fig. 1803.
[Fig. 1803] shows a tool b secured in a hole provided in a stout bar a by the set-screw c. The tool in this case being rigidly held the cutting edge is apt to rub against the work during the upward stroke and become rapidly dulled. To avoid this, various devices have been employed, but before describing them it will be well to point out that the shape of the tool has an important bearing upon this point.
Fig. 1804.
Fig. 1805.
In [Fig. 1804], for example, is a tool t bolted to the box b at the end of the slide s. w is a piece of work having the cut c taken off it. Now suppose that a is the centre of motion or fulcrum from which the spring of the tool takes place (and there is sure to be a little spring under a heavy cut), then the point of the tool will spring in the direction of the arrow e, and will cut deeper to the amount of its spring; but during the up stroke the tool being released from pressure will not spring, and therefore will partly or quite clear the cut according to the amount of the spring. This desirable action may be increased by giving the face of the tool which meets the cutting a slight degree of side rake, as shown in [Fig. 1805], in which s is the slide, t the tool, b the box, and f the direction of the tool spring, which takes place in this case from the pressure of the cutting in its resistance to being bent out of the straight line.