Fig. 2180.
But in tools driven by power, and therefore accurately guided in their line of motion, it is preferable to let the bottom face clear the work surface, save at the extreme cutting edge. The front face of the wedge or tool is that which mainly determines its keenness, as may be seen from [Fig. 2180], in which we have the wedge or tool differently placed with relation to the work, that in position a obviously being the keenest and less liable to break from the strain of the cutting process.
If we now turn our attention to that class of chisel or wedge-shaped tools in which the cutting edge is not a straight line, but may be stepped or curved—as, for example, the carpenter’s plane blade—we shall find that so long as the blade stands at a right angle to the surface it is operating upon, as in [Fig. 2183] at b, the shape of surface it cuts will exactly correspond to the shape of its cutting edge; but so soon as the tool is inclined to its line of motion its cutting edge will, if curved, produce a different degree of curvature on the work.
Fig. 2181.
