developed, especially for turning duplicate parts in
quantity, is illustrated by the design of turret lathe the turret and
head of which is shown in Fig. 30. This machine has two spindles and a
large flat turret which holds a double set of tools, so that two
duplicate castings or forgings can be turned at the same time. It was
designed primarily for chuck work and can be used as a single-spindle
machine if desirable. When two spindles are employed for machining two
duplicate parts simultaneously, considerably more time is required for
setting up the machine than is necessary for the regular single-spindle
type, but it is claimed that the increased rate of production obtained
with the two-spindle design more than offsets this initial handicap.
The manufacturers consider the single-spindle machine the best type for
ordinary machine building operations, regardless of whether the work is
turned from the bar or is of the chucking variety. On the other hand,
the double-spindle type is preferred when work is to be produced in such
quantities that the time for setting up the machine becomes a secondary
consideration.

[Illustration: Fig. 31. Diagram showing Tool Equipment and Successive
Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe]

When the double-spindle machine is used as a single-spindle type, a
chuck 17 inches in diameter is used, and when both spindles are in
operation, two 9-inch chucks are employed. The general outline of the
turret is square, and the tools are rigidly held, with a minimum amount
of overhang, by means of tool-blocks and binding screws connected with
the clamping plates. Two duplicate sets of tools are clamped to each
side of the turret and these operate simultaneously on the two pieces
held in the chucks or on faceplates. Primarily the turret is used in
but four positions, but when a 17-inch chuck or faceplate is employed,
corner blocks may be held by the clamping plates in which tools are
supported, giving, if necessary, four additional operations by indexing
the turret to eight positions.

A typical job to demonstrate the application of the double-spindle flat
turret lathe is illustrated in Fig. 31. The parts to be turned are
sprocket wheels which are held in the two 9-inch chucks. At the first
position of the turret (which is the one illustrated), the inside is
rough-bored by tools _A_. At the second position of the turret, tools
_B_ rough-face the inner sides of the flan