All the different types of turning machines now in use originated from
the lathe. Many of these tools, however, do not resemble the lathe
because, in the process of evolution, there have been many changes made
in order to develop turning machines for handling certain classes of
work to the best advantage. The machine illustrated in Fig. 1 belongs to
the lathe family and is known as a vertical boring and turning mill.
This type, as the name implies, is used for boring and turning
operations, and it is very efficient for work within its range. The part
to be machined is held to the table _B_ either by clamps or in chuck
jaws attached to the table. When the machine is in operation, the table
revolves and the turning or boring tools (which are held in tool-blocks
_T_) remain stationary, except for the feeding movement. Very often more
than one tool is used at a time, as will be shown later by examples of
vertical boring mill work. The tool-blocks _T_ are inserted in tool-bars
_T_{1}_ carried by saddles _S_ which are mounted on cross-rail _C_. Each
tool-head (consisting of a saddle and tool-bar) can be moved
horizontally along cross-rail _C_, and the tool-bars _T_{1}_ have a
vertical movement. These movements can be effected either by hand or
power.

When a surface is being turned parallel to the work table, the entire
tool-head moves horizontally along the cross-rail, but when a
cylindrical surface is being turned, the tool-bar moves vertically. The
tool-heads are moved horizontally by the screws _H_ and _H_{1}_, and the
vertical feed for the tool-bars is obtained from the splined shafts _V_
and _V_{1}_, there being a separate screw and shaft for each head so
that the feeding movements are independent. These feed shafts are
rotated for the power feed by vertical shafts _A_ and _A_{1}_ on each
side of the machine.

These vertical shafts connect with the feed shafts through bevel and
spur gears located at the ends of the cross-rail. On most boring mills,
connection is made with one of the splined shafts _V_ or screw _H_, by a
movable gear, which is placed on whichever shaft will give the desired
direction of feed. The particular machine illustrated is so arranged
that either the right or left screw or feed shaft can be engaged by
simply shifting levers _D_{1}_ or _D_.

[Illustration: Fig. 1. Gisholt Vertical Boring and Turning Mill]

The amount of feed per revolution of the table is varied for each
tool-head by feed-c