d and then turn the ends to the required radius by placing the
head in the lathe. After both sets of cutters have been turned in this
way, they are ground to shape and then hardened.

[Illustration: Fig. 7. Cutter-heads equipped with Adjustable Tools]

Boring cutters intended for roughing and finishing cuts are shown in the
detail view Fig. 8 at _A_ and _B_, respectively. The side of the
roughing cutter _A_ is ground to a slight angle _c_ to provide clearance
for the cutting edge, and the front has a backward slope _s_ to give the
tool keenness. This tool is a good form to use for roughing cuts in cast
iron. The finishing tool at _B_ has a broad flat edge _e_ and it is
intended for coarse feeds and light cuts in cast iron. If a round
cutting edge is used for finishing, a comparatively fine feed is
required in order to obtain a smooth surface. The corners of tool _B_
are rounded and they should be ground to slope inward as shown in the
plan view. The top or ends _d_ of both of these tools are "backed off"
slightly to provide clearance. This clearance should be just enough to
prevent the surface back of the cutting edge from dragging over the
work. Excessive end clearance not only weakens the cutting edge, but
tends to cause chattering. As a finishing tool cuts on the upper end
instead of on the side, the front should slope backward as shown in the
side view, rather than sidewise as with a roughing cutter. The angle of
the slope should be somewhat greater for steel than cast iron, unless
the steel is quite hard, thus requiring a strong blunt tool.

[Illustration: Fig. 8. Boring Tools for Roughing and Finishing Cuts]

=Cylinder Boring.=--Fig. 9 illustrates the use of a cutter-head for
cylinder boring. After the cylinder casting is set on the platen of the
machine, the boring-bar with the cutter-head mounted on it is inserted
in the spindle. The bar _B_ has a taper shank and a driving tang similar
to a drill shank, which fits a taper hole in the end of the spindle. The
cutter-head _C_ is fastened to the bar so that it will be in the
position shown when the spindle is shifted to the right, as the feeding
movement (with this particular machine) is to be in the opposite
direction. The casting _A_ should be set central with the bar by
adjusting the work-table vertically and laterally, if necessary, and the
outer support _F_ should be moved close to the work, to make the bar as
rigid as possible.

The cylinder is now ready t