In this case let us assume that the clearance angle D is 15 degrees, as well as in the following figures.
Suppose we have a piece of tough steel, and the tool holder is raised so that the point of the tool is at the 15 degree line E, as shown in [Fig. 36], in which case the clearance line D is at right angles to the line E. The line E is 15 degrees above the center line C.
The Setting Angle.—Now, it is obvious that if the tool should be raised higher than the line E it would run out of work, because the clearance surface of the tool would ride up over the surface cut by the edge of the tool.
If, on the other hand, the tool should be placed lower, toward the line C, the tendency would be to draw in the tool toward the center of the work A
In [Fig. 37] the tool has its point elevated, in which case it must be lowered so the point will touch the work nearer the center line C.
The foregoing arrangement of the tools will be found to be effective where the material is soft and not too tough as with aluminum.
Bad Practice.—Figs. 38 and 39 show illustrations of bad practice which should never be resorted to. [Fig. 38] shows the tool, held in a horizontal position, but with its point below the center line C. With any rough metal the tool could not possibly work, except to act as a scraper, and if it should be used in that position on cast iron, the tool itself would soon be useless.