Fig. 1655.
It is essential, therefore, to carry the tool at the back of the tool post as shown, and for curves that are arcs of circles tools such as in [Fig. 1655] may be employed, or a circular disk will answer, possessing the advantage that its shape may be maintained by grinding its flat face to resharpen it.
Cutters of the kind shown in [Fig. 1655] may be made to possess several important advantages aside from their smooth action: thus they may be made after the principle explained with reference to the Brown & Sharpe rotary cutters for gear-teeth, in which case the front face only need be ground to resharpen them, and their shapes will remain unaltered, and they may be given different degrees of front rake by placing packing between one side and the holder, and any number of different shaped cutters may be fitted to the same stock.
Tool Holders for Planing Machines.—The advantages of tool holders for planing machines are equally as great as those already described for lathes, but as applied to planing machines there is the additional advantage that the clearance necessary on the tool is less variable for planer work than for lathe work, because in lathe work the diameter of the work as well as the rate of tool feed affects the tool clearance, whereas in planer work the tool feed is put on before the tool begins its cutting action; hence the degree of clearance is neither affected by the size of the work nor by the rate of feed, and as a result the tools may be given a definite and constant amount of clearance.
Fig. 1656.
Fig. 1657.