rder to give the toolslide time to operate properly. A maximum of
180 teeth per minute is recommended, and, if wide forming tools are
used, it might be advisable to reduce the speed so low that only 8 teeth
per minute would be relieved. It is also essential to use a tool having
a keen edge, and the toolslide should work freely but be closely
adjusted to the dovetail of the lower slide. Before beginning to back
off the teeth, it is a good plan to color the work either by heating it
or dipping into a strong solution of copper sulphate. This will enable
one to see plainly the cutting action of the tool in order to stop
relieving at the proper time.

[Illustration: Fig. 41. Relieving a Right-hand Tap]

Fig. 40 shows a method of relieving the teeth of an angular cutter. For
an operation of this kind the toolslide is swiveled around at right
angles to the side that is to be relieved. By the use of an additional
universal joint and bearing to permit the toolslide to be swung to a
90-degree angle, the teeth of counterbores, etc., can be relieved on the
ends. When the attachment is used for relieving inside work, such as
hollow mills and threading dies, the eccentric which controls the travel
of the toolslide is set so that the relieving movement is away from the
axis of the cutter instead of toward it. This change is made by the
toothed coupling previously referred to, which connects the cam lever
and oscillating shaft, the latter being turned beyond the zero mark in a
clockwise direction as far as is necessary to obtain the desired amount
of travel. For internal work it is also necessary to change the position
of the opposing spring of the toolslide, so that it will press against
the end of the slide and prevent the tool from jumping into the work.

[Illustration: Fig. 42. Relieving a Hob having Spiral Flutes]

Fig. 41 shows how a right-hand tap is relieved. The ordinary practice is
to first set the tool the same as for cutting a thread. The motion of
the toolslide is then adjusted so that the tool on the forward stroke
will meet the front of each tooth, and start back as soon as the tool
leaves the end of the land or top of the tooth. Taps having a left-hand
thread can be relieved by two different methods. With the first method
the cut starts at the cutting edge of each tooth, and ends at the
"heel," the tool moving in toward the center of the work. With the
second method, the cut begins at the heel and discontinues at the