Fig. 1806.
In [Fig. 1806] is a device for obviating to some extent this defect. a a is the tool box or bar containing a tool-holding piece pivoted at c, the tool being secured therein by the set-screw e b. A spiral spring sustains the weight of the pivoted piece and of the tool. During the down stroke the spiral spring holds the pivoted piece against the box or bar a, while during the up stroke the pivoted piece allows the tool to swing from the pivot c as denoted by the arrow d. In this case the friction on the tool edge is that due to overcoming the resistance of the spring only.
Fig. 1807.
In round-nose tools that are slight, and which from having a maximum length of cutting edge are very subject to spring, additional strength may be given the tool by swelling it out at the back, as denoted by the dotted line b in [Fig. 1807].
Fig. 1808.