olslide is so adjusted that the tool
will meet the front of each tooth and the return movement begin promptly
after the tool leaves the back end of the tooth.

[Illustration: Fig. 39. Relieving a Formed Cutter]

These attachments differ somewhat in their construction and arrangement
but the principle of their operation is similar. Fig. 38 shows a Hendey
relieving attachment applied to a lathe. A bracket carrying the gearing
_A_ through which the attachment is driven is mounted upon the main gear
box of the lathe, and the special slide _B_, which is used when
relieving, is placed on the cross-slide after removing the regular
compound rest. The gears at _A_ are changed to suit the number of flutes
or gashes in the cutter, tap or whatever is to be relieved. If we assume
that the work is a formed milling cutter having nine teeth, then with
this particular attachment, a gear having 90 teeth would be placed on
the "stud" and a 40-tooth gear on the cam-shaft, the two gears being
connected by a 60-tooth intermediate gear. With this combination of
gearing, the toolslide would move in and out nine times for each
revolution of the work, so that the tool could back off the top of each
tooth. (The gearing to use for various numbers of flutes is shown by an
index plate on the attachment.) The amount of relief is varied to suit
the work being done, by means of a toothed coupling which makes it
possible to change the relative position between the eccentric which
actuates the toolslide and the cam lever, thereby lengthening or
shortening the reciprocating travel of the tool.

[Illustration: Fig. 40. Relieving Side of Angular Milling Cutter]

=Application of Relieving Attachment.=--Some typical examples of the
kind of work for which the relieving attachment is used are shown in
Figs. 39 to 42, inclusive. Fig. 39 shows how a formed milling cutter is
relieved. The toolslide is set at right angles to the axis of the work,
and the tool moves in as each tooth passes, and out while crossing the
spaces or flutes between the teeth. As the result of this movement, the
tops of the teeth are backed off eccentrically but the form or shape is
the same from the front to the back of the tooth; hence, a cutter that
has been relieved in this way can be ground repeatedly without changing
the profile of the teeth, provided the faces are ground so as to lie in
a radial plane.

When relieving, the cutting speed should be much less than when turning
in o