orged from the bar, and when the cutting ends have been ground down
considerably it is necessary to forge a new end. To eliminate the
expense of this continual dressing of tools and also to effect a great
reduction in the amount of tool steel required, tool-holders having
small inserted cutters are used in many shops. A tool-holder of this
type, for outside turning, is shown in Fig. 3. The cutter _C_ is held in
a fixed position by the set-screw shown, and it is sharpened,
principally, by grinding the end, except when it is desired to give the
top of the cutter a different slope from that due to its angular
position. Another inserted-cutter turning tool is shown in Fig. 4, which
is a heavy type intended for roughing. The cutter in this case has teeth
on the rear side engaging with corresponding teeth cut in the clamping
block which is tightened by a set-screw on the side opposite that shown.
With this arrangement, the cutter can be adjusted upward as the top is
ground away.

[Illustration: Fig. 5. Parting Tool with Inserted Blade]

[Illustration: Fig. 6. Boring Tool with Inserted Cutter and Adjustable
Bar]

A parting tool of the inserted blade type is shown in Fig. 5. The blade
_B_ is clamped by screw _S_ and also by the spring of the holder when
the latter is clamped in the toolpost. The blade can, of course, be
moved outward when necessary. Fig. 6 shows a boring tool consisting of a
holder _H_, a bar _B_ that can be clamped in any position, and an
inserted cutter _C_. With this type of boring tool, the bar can be
extended beyond the holder just far enough to reach through the hole to
be bored, which makes the tool very rigid. A thread tool of the holder
type is shown in Fig. 7. The angular edge of the cutter _C_ is
accurately ground by the manufacturers, so that the tool is sharpened
by simply grinding it flat on the top. As the top is ground away, the
cutter is raised by turning screw _S_, which can also be used for
setting the tool to the proper height.

=The Position of Turning Tools.=--The production of accurate lathe work
depends partly on the condition of the lathe used and also on the care
and judgment exercised by the man operating it. Even though a lathe is
properly adjusted and in good condition otherwise, errors are often made
which are due to other causes which should be carefully avoided. If the
turning tool is clamped so that the cutting end extends too far from the
supporting block, the downward spri