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Introduction
Lathes were developed as early as the 15th century and were known as "bow"
lathes. The operator rotated the workpiece by drawing a bow back and forth,
either by hand or with the use of a foot treadle. Next came Bessons lathe
in 1568, which was driven by a cord passing over a pulley above the machine.
This in turn drove two other pulleys on the same shaft which rotated the
workpiece and a crude, wooden lead screw, which in turn allowed the operator
to remove metal from the piece being machined. The screw cutting lathe
originates in the 17th century. Development and advancements have continued
and today we have sophisticated computerized controlled lathes.
Lathes have allowed man to reshape, machine and manufacture many precision
cylindrical components made of various types of metal, wood, plastics, and
other materials. Without the lathe, man would still be trying to produce
cylindrical components
in some crude fashion or another. However, because of advanced technology,
the lathe has allowed man to become an important asset in developing and
machining many precision components needed to operate and function in many
areas of our industrial complex.
2. Lathes Types and Uses.
a. General. The lathe is a machine tool used principally for shaping
articles of metal, wood, or other material. All lathes, except the vertical
turret type, have one thing in common for all usual machining operations;
the workpiece is held and rotated around a horizontal axis while being
formed to size and shape by a cutting tool. The cutter bit is held either
by hand or by a mechanical holder, then applied to the workpiece. Principal
capabilities of the lathe are forming straight, tapered, or irregularly
outlined cylinders, facing or radial turning cylindrical sections, cutting
screw threads, and boring or enlarging internal diameters. The typical
lathe provides a variety of rotating speeds and suitable manual and
automatic controls for moving the cutting tool.
b. Types of Lathes. Lathes can be conveniently classified as engine
lathes, turret lathes, and special purpose lathes. All engine lathes and
most turret and special purpose lathes have horizontal spindles and, for
that reason, are sometimes referred to as horizontal lathes. The smaller
lathes in all classes may be classified as bench lathes or floor or pedestal
lathes, the reference in this case being to the means of support.
c. Engine Lathes.
(1) General. The engine lathe is intended for general purpose lathe work
and is the usual lathe found in the machine shop. The engine lathe may be
bench or floor mounted; it may be referred to as a toolroom-type lathe, or a
sliding-gap or extension-type lathe. The engine lathe consists mainly of a
headstock, a tailstock, a carriage, and a bed upon which the tailstock and
carriage move. Most engine lathes are back-geared and high torque, which is
required for machining large diameter workpieces and taking heavy cuts. The
usual engine lathe has longitudinal power and crossfeeds for moving the
carriage. It has a lead screw with gears to provide various controlled
feeds for cutting threads. Engine lathes are made in various sizes; the size is determined by
the manufacturer. Generally, the size is determined by the following
measurements: either (a) the diameter of the workpiece will swing over the
bed, or (b) it will swing over the cross-slide, and © the length of the
bed, or (d) the maximum distance between centers. For example, using method
(a) and ©, a 14 inch x 6-foot lathe has a bed that is 6 feet long and will
swing work (over the bed) up to 14 inches in diameter. The maximum distance
between centers indicates the dimension, in inches, of the longest length of
material that can be placed in the lathe.
(2) Bench-Type Engine Lathe.
(a) The bench-type engine lathe (figure 1 on the following page), is the
most common general purpose screw cutting lathe normally found in a small
shop. It commonly has an 8 to 12 inch swing and a 3 to 5 foot bed length,
the size being limited by the practicality of bench mounting. The bench
upon which the lathe is mounted may be a standard wood-topped shop bench or
a special metal lathe bench with drawers for storing the lathe accessories.
(b) The bench-type engine lathe is generally powered by an electric
motor, mounted to the bench behind the lathe headstock, and is driven by
means of a flat leather belt. Some bench lathes use an underneath motor
drive where the drive belt passes through a hole in the bench. This
arrangement is convenient where space in the shop is limited. The benchtype
engine lathe is generally equipped with the necessary tools, chucks,
lathe dogs, and centers for normal operation. The lathe may have a quickchange
gearbox for rapid change of threading feeds, or gears may have to be
installed singly or in combination to achieve the proper threading feeds.
The bench lathe may or may not have a power-operated crossfeed drive.