being bored while standing in a vertical position. If, however,
the cylinder is bored while in the position in which it will be placed
in the assembled engine, this trouble is practically eliminated.

There is a difference of opinion among machinists as to the proper shape
of the cutting point of a boring tool for finishing cuts, some
contending that a wide cutting edge is to be preferred, while others
advocate the use of a comparatively narrow edge with a reduced feed. It
is claimed, that the narrow tool produces a more perfect bore, as it is
not so easily affected by hard spots in the iron, and it is also pointed
out that the minute ridges left by the narrow tool are an advantage
rather than a disadvantage, as they form pockets for oil and aid in
lubricating the cylinder. It is the modern practice, however, to use a
broad tool and a coarse feed for the light finishing cut, provided the
tool does not chatter.

The type of machine tool used for boring cylinders, and also the method
of procedure is determined largely by the size of the work and the
quantity which is to be machined. The turret lathe, as well as
horizontal and vertical boring mills, is used for this work, and in
automobile factories or other shops where a great many cylinders are
bored, special machines and fixtures are often employed.

[Illustration: Fig. 10. Boring a Duplex Cylinder on a Horizontal
Machine]

=Boring a Duplex Gasoline Engine Cylinder.=--The method of holding work
on a horizontal boring machine depends on its shape. A cylinder or other
casting having a flat base can be clamped directly to the platen, but
pieces of irregular shape are usually held in special fixtures. Fig. 10
shows how the cylinder casting of a gasoline engine is set up for the
boring operation. The casting _W_ is placed in a fixture _F_ which is
clamped to the machine table. One end of the casting rests on the
adjustable screws _S_ and it is clamped by set-screws located in the top
and sides of the fixture. There are two cylinders cast integral and
these are bored by a short stiff bar mounted in the end of the spindle
and having cutters at the outer end. A long bar of the type which passes
through the work and is supported by the outboard bearing _B_, could not
be used for this work, because the top of each cylinder is closed.

When one cylinder is finished the other is set in line with the spindle
by adjusting the work-table laterally. This adjustment is effected by