eed.
Obviously, if the straight or flat part of the cutting edge is in line
with the travel of the tool, the cut will be smooth and free from
ridges, even though the feed is coarse, and by using a coarse feed the
cut is taken in less time; but such a tool cannot be used on work that
is not rigid, as chattering would result. Therefore, a smaller cutting
point and a reduced feed would have to be employed. Tools with broad
flat cutting edges and coarse feeds are often used for taking finishing
cuts in cast iron, as this metal offers less resistance to cutting than
steel, and is less conducive to chattering.

The shape of a tool (as viewed from the top) which is intended for a
more specific purpose than regular turning, can be largely determined by
simply considering the tool under working conditions. This point may be
illustrated by the parting tool _D_ which, as previously stated, is used
for cutting grooves, squaring corners, etc. Evidently this tool should
be widest at the cutting edge; that is, the sides _d_ should have a
slight amount of clearance so that they will not bind as the tool is fed
into a groove. As the tool at _E_ is for cutting a V-thread, the angle
[alpha] between its cutting edges must equal the angle between the sides
of a V-thread, or 60 degrees. The tool illustrated at _F_ is for cutting
inside square threads. In this case the width _w_ should be made equal
to one-half the pitch of the thread (or slightly greater to provide
clearance for the screw), and the sides should be given a slight amount
of side clearance, the same as with the parting tool _D_. So we see that
the outline of the tool, as viewed from the top, must conform to and be
governed by its use.

=Direction of Top Slope for Turning Tools.=--Aside from the question of
the shape of the cutting edge as viewed from the top, there remains to
be determined the amount of clearance that the tool shall have, and also
the slope (and its direction) of the top of the tool. By the top is
meant that surface against which the chip bears while it is being
severed. It may be stated, in a general way, that the direction in which
the top of the tool should slope should be away from what is to be the
_working part_ of the cutting edge. For example, the working edge of a
roughing tool _A_ (Fig. 11), which is used for heavy cuts, would be,
practically speaking, between points _a_ and _b_, or, in other words,
most of the work would be done by this part of the