are
performed at the same setting will be referred to later. The horizontal
boring machine also makes it possible to machine duplicate parts without
the use of jigs, which is important, especially on large work, owing to
the cost of jigs.

=Drilling and Boring--Cutters Used.=--Holes are drilled in a horizontal
machine by simply inserting a drill of required size either directly in
the spindle _S_ (see Fig. 1), or in a reducing socket, and then feeding
the spindle outward either by hand or power. When a hole is to be bored,
a boring-bar _B_{1}_ is inserted in the spindle and the cutter is
attached to this bar. The latter is then fed through the hole as the
cutter revolves. The distinction made by machinists between drilling and
boring is as follows: A hole is said to be drilled when it is formed by
sinking a drill into solid metal, whereas boring means the enlargement
of a drilled or cored hole either by the use of a single boring tool, a
double-ended cutter which operates on both sides of the hole, or a
cutter-head having several tools.

There are various methods of attaching cutters to boring-bars and the
cutters used vary for different classes of work. A simple style of
cutter which is used widely for boring small holes is shown at _A_ in
Fig. 3. The cutter _c_ is made from flat stock and the cutting is done
by the front edges _e_ and _e_{1}_, which are beveled in opposite
directions. The cutter is held in the bar by a taper wedge _w_ and it
is centered by shoulders at _s_, so that the diameter of the hole will
equal the length across the cutter. The outer corners at the front
should be slightly rounded, as a sharp corner would be dulled quickly.
These cutters are made in different sizes and also in sets for roughing
and finishing. The roughing cutter bores holes to within about 1/32 inch
of the finish size and it is then replaced by the finishing cutter. A
cutter having rounded ends, as shown by the detail sketch _a_, is
sometimes used for light finishing cuts. These rounded ends form the
cutting edges and give a smooth finish.

[Illustration: Fig. 3. Boring-cutters of Different Types]

Another method of holding a flat cutter is shown at _B_. The conical end
of a screw bears against a conical seat in, the cutter, thus binding the
latter in its slot. The conical seat also centers the cutter. A very
simple and inexpensive form of cutter is shown at _C_. This is made from
a piece of round steel, and it is held in th