rinding
than to ruin the tool by burning, in an attempt to sharpen it quickly.
Of course, what has been said about burning applies more particularly to
carbon steel, but even self-hardening steels are not improved by being
over-heated at the stone. In some shops, tools are ground to the
theoretically correct shape in special machines instead of by hand. The
sharpened tools are then kept in the tool-room and are given out as they
are needed.

=Cutting Speeds and Feeds.=--The term cutting speed as applied to
turning operations is the speed in feet per minute of the surface being
turned, or, practically speaking, it is equivalent to the length of a
chip, in feet, which would be turned in one minute. The term cutting
speed should not be confused with revolutions per minute, because the
cutting speed depends not only upon the speed of the work but also upon
its diameter. The feed of a tool is the amount it moves across the
surface being turned for each revolution; that is, when turning a
cylindrical piece, the feed is the amount that the tool moves sidewise
for each revolution of the work. Evidently the time required for turning
is governed largely by the cutting speed, the feed, and the depth of the
cut; therefore, these elements should be carefully considered.

Cutting Speeds and Feeds for Turning Tools[1]

+---------------------------------++---------------------------------+
| Steel--Standard 7/8-inch Tool ||Cast Iron--Standard 7/8-inch Tool|
+-----+-----+---------------------++-----+-----+---------------------+
| | | Speed in Feet per || | | Speed in Feet per |
|Depth|Feed | Minute for a Tool ||Depth|Feed | Minute for a Tool |
| of | in | which is to last || of | in | which is to last |
| Cut | In- | 1-1/2 Hour before || Cut | In- | 1-1/2 Hour before |
| in |ches | Re-grinding || in |ches | Re-grinding |
| In- | +------+------+-------++ In- | +-------+------+------+
|ches | | Soft |Medium| Hard ||ches | | Soft |Medium| Hard |
| | |Steel |Steel |Steel || | | Cast | Cast | Cast |
| | | | | || | | Iron | Iron | Iron |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
| | 1/64| 476 | 238 | 108 || | 1/16| 122 | 61.2 | 35.7 |
|3/32 | 1/32| 325 | 162 | 73.8 ||3/32 | 1/8 | 86.4 | 43.2 | 25.2 |
| | 1/16| 222 | 111 | 50.4 ||