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					                       Lathe Machine


A lathe (pronounced /ˈ   leɪð/) is a machine tool which spins a
block of material to perform various operations such as cutting,
sanding, knurling, drilling, or deformation with tools that are
applied to the workpiece to create an object which has
symmetry about an axis of rotation.

Lathes are used in woodturning, metalworking, metal spinning,
and glassworking. Lathes can be used to shape pottery, the best-
known design being the potter's wheel. Most suitably equipped
metalworking lathes can also be used to produce most solids of
revolution, plane surfaces and screw threads or helices.
Ornamental lathes can produce three-dimensional solids of
incredible complexity. The material is held in place by either one
or two centers, at least one of which can be moved horizontally
to accommodate varying material lengths.

Examples of objects that can be produced on a lathe include
candlestick holders, cue sticks, table legs, bowls, baseball bats,
musical instruments (especially woodwind instruments),
crankshafts and camshafts.

History

The lathe is an ancient tool, dating at least to the Egyptians and
known and used in Assyria, Greece, the Roman and Byzantine
Empires.




A turned wood bowl with natural edges
The origin of turning dates to around 1300BC when the Egyptians
first developed a two-person lathe. One person would turn the
wood work piece with a rope while the other used a sharp tool to
cut shapes in the wood. The Romans improved the Egyptian
design with the addition of a turning bow. Early bow lathes were
also developed and used in Germany, France and Britain. In the
Middle Ages a pedal replaced hand-operated turning, freeing both
the craftsman's hands to hold the woodturning tools. The pedal
was usually connected to a pole, often a straight-grained sapling.
The system today is called the "spring pole" lathe (see
Polelathe). Spring pole lathes were in common use into the early
20th Century. A two-person lathe, called a "great lathe", allowed
a piece to turn continuously (like today's power lathes). A master
would cut the wood while an apprentice turned the crank. [1]

During the industrial revolution, mechanized power was applied
to the lathe via steam engines and line shafting, allowing faster
and easier work. The design of lathes diverged between
woodworking and metalworking to a greater extent than in
previous centuries. Metalworking lathes evolved into heavier
machines with thicker, more rigid parts. The application of
leadscrews, slide rests, and gearing produced commercially
practical screw-cutting lathes. Between the late 19th and mid
20th centuries, individual electric motors at each lathe replaced
line shafting as the power source. Beginning in the 1950s,
servomechanisms were applied to the control of lathes and other
machine tools via numerical control (NC), which often was
coupled with computers to yield computerized numerical control
(CNC). Today manually controlled and CNC lathes coexist in the
manufacturing industries.

Description

Parts
Parts of a wood lathe

A lathe may or may not have a stand (or legs), which sits on the
floor and elevates the lathe bed to a working height. Some lathes
are small and sit on a workbench or table, and do not have a
stand.

Almost all lathes have a bed, which is (almost always) a
horizontal beam (although some CNC lathes have a vertical beam
for a bed to ensure that swarf, or chips, falls free of the bed). A
notable exception is the Hegner VB36 Master Bowlturner, a
woodturning lathe designed for turning large bowls, which in its
basic configuration is little more than a very large floor-standing
headstock.

At one end of the bed (almost always the left, as the operator
faces the lathe) is a headstock. The headstock contains high-
precision spinning bearings. Rotating within the bearings is a
horizontal axle, with an axis parallel to the bed, called the
spindle. Spindles are often hollow, and have exterior threads
and/or an interior Morse taper on the "inboard" (i.e., facing to the
right / towards the bed) by which accessories which hold the
workpiece may be mounted to the spindle. Spindles may also
have exterior threads and/or an interior taper at their "outboard"
(i.e., facing away from the bed) end, and/or may have a
handwheel or other accessory mechanism on their outboard end.
Spindles are powered, and impart motion to the workpiece.

The spindle is driven, either by foot power from a treadle and
flywheel or by a belt drive to a power source. In some modern
lathes this power source is an integral electric motor, often
either in the headstock, to the left of the headstock, or beneath
the headstock, concealed in the stand.

In addition to the spindle and its bearings, the headstock often
contains parts to convert the motor speed into various spindle
speeds. Various types of speed-changing mechanism achieve
this, from a cone pulley or step pulley, to a cone pulley with back
gear (which is essentially a low range, similar in net effect to the
two-speed rear of a truck), to an entire gear train similar to that
of a manual-shift auto transmission. Some motors have
electronic rheostat-type speed controls, which obviates cone
pulleys or gears.

The counterpoint to the headstock is the tailstock, sometimes
referred to as the loose head, as it can be positioned at any
convenient point on the bed, by undoing a locking nut, sliding it
to the required area, and then relocking it. The tailstock contains
a barrel which does not rotate, but can slide in and out parallel to
the axis of the bed, and directly in line with the headstock
spindle. The barrel is hollow, and usually contains a taper to
facilitate the gripping of various type of tooling. Its most common
uses are to hold a hardened steel centre, which is used to
support long thin shafts while turning, or to hold drill bits for
drilling axial holes in the work piece. Many other uses are
possible.

Metalworking lathes have a carriage (comprising a saddle and
apron) topped with a cross-slide, which is a flat piece that sits
crosswise on the bed, and can be cranked at right angles to the
bed. Sitting atop the cross slide is a toolpost, which holds a
cutting tool which removes material from the workpiece. There
may or may not be a leadscrew, which moves the cross-slide
along the bed.

Woodturning and metal spinning lathes do not have cross-slides,
but rather have banjos, which are flat pieces that sit crosswise
on the bed. The position of a banjo can be adjusted by hand; no
gearing is involved. Ascending vertically from the banjo is a
toolpost, at the top of which is a horizontal toolrest. In
woodturning, hand tools are braced against the tool rest and
levered into the workpiece. In metal spinning, the further pin
ascends vertically from the tool rest, and serves as a fulcrum
against which tools may be levered into the workpiece.

Accessories

Unless a workpiece has a taper machined onto it which perfectly
matches the internal taper in the spindle, or has threads which
perfectly match the external threads on the spindle (two things
which almost never happen), an accessory must be used to
mount a workpiece to the spindle.

A workpiece may be bolted or screwed to a faceplate, a large flat
disk that mounts to the spindle. Alternatively faceplate dogs may
be used to secure the work to the faceplate.

A workpiece may be clamped in a three- or four-jaw chuck, which
mounts directly to the spindle or mounted on a mandrel.

In precision work (and in some classes of repetition work),
cylindrical workpieces are invariably held in a collet inserted into
the spindle and secured either by a drawbar, or by a collet
closing cap on the spindle. Suitable collets may also be used to
mount square or hexagonal workpieces. In precision toolmaking
work such collets are usually of the draw in variety, where, as
the collet is tightened, the workpiece moves slightly back into
the headstock, whereas for most repetition work the dead length
variety is preferered as this ensures that the position of the
workpiece does not move as the collet is tightened, so the
workpiece can be set in the lathe to a fixed position and it will
not move on tightening the collet.

A soft workpiece (wooden) may be pinched between centers by
using a spur drive at the headstock, which bites into the wood
and imparts torque to it.
Live center (top) Dead center (bottom)

A soft dead center is used in the headstock spindle as the work
rotates with the centre. Because the centre is soft it can be
trued in place before use. The included angle is 60 degrees.
Traditionally a hard dead center is used together with suitable
lubricant in the tailstock to support the workpiece. In modern
practice the dead center is frequently replaced by a live center
or (revolving center) as it turns freely with the workpiece usually
on ball bearings, reducing the frictional heat, which is especially
important at high RPM. A lathe carrier or lathe dog may also be
employed when turning between two centers.

In woodturning, one subtype of a live center is a cup center,
which is a cone of metal surrounded by an annular ring of metal
that decreases the chances of the workpiece splitting.

A circular metal plate with even spaced holes around the
periphery, mounted to the spindle, is called an "index plate". It
can be used to rotate the spindle a precise number of degrees,
then lock it in place, facilitating repeated auxiliary operations
done to the workpiece.

Modes of use

When a workpiece is fixed between the headstock and the
tailstock, it is said to be "between centers". When a workpiece is
supported at both ends, it is more stable, and more force may be
applied to the workpiece, via tools, at a right angle to the axis of
rotation, without fear that the workpiece may break loose.

When a workpiece is fixed only to the spindle at the headstock
end, the work is said to be "face work". When a workpiece is
supported in this manner, less force may be applied to the
workpiece, via tools, at a right angle to the axis of rotation, lest
the workpiece rip free. Thus, most work must be done axially,
towards the headstock, or at right angles, but gently.

When a workpiece is mounted with a certain axis of rotation,
worked, then remounted with a new axis of rotation, this is
referred to as "eccentric turning" or "multi axis turning". The
result is that various cross sections of the workpiece are
rotationally symmetric, but the workpiece as a whole is not
rotationally symmetric. This technique is used for camshafts,
various types of chair legs.

Varieties

The smallest lathes are "jewelers lathes" or "watchmaker
lathes", which are small enough that they may be held in one
hand. The workpieces machined on a jeweler's lathes are metal,
jeweler's lathes can be used with hand held "graver" tools or
with compound rests that attach to the lathe bed. Graver tools
are generally supported by a T-rest, not fixed to a cross slide or
compound rest. The work is usually held in a collet. Three
spindle bore sizes to receive the collets are common, namely 6,
m/m , 8;mm and 10 m/m these dimensions refer to the straight
shank body size of the collet. The term W/W refers to the
Webster/Whitcomb collet and lathe , this lathe was invented by
the American Watch Tool Company of Waltham Ma. The name
Webster/ Whitcomb was the last names of the founders of that
Company. Most of the lathes that are commonly refered to as
watchmakers lathes are of this design. Most of the watchmakers
lathes built anywhere in the world after the introduction of this
lathe in 1888 were copies of this lathe design. In 1909 the
American Watch Tool company introduced the Magnus type
collet ( the 10 m/m body size collet)using the same basic lathe ,
originally as the Webster/Whitcomb Magnus. In 1918 the
American Watch Tool Company was purchased by the former
superintendant of the American watch Tool Company Frederick
William Derbyshire , the names Webster/Whitcomb and Magnus
are STILL trade names of F.W.Derbyshire, Inc. the company
founded by Frederick Derbyshire in 1911 and these collets are
still correctly produced ( nominal thread size 7m/m 6.95 m/m x
.625 m/m pitch NOTE many poor quality copies reduce the pitch
diameter and run 40 threads per inch) by F.W. Derbyshire, Inc.
today Two patterns of bed are common: the WW (Webster
Whitcomb) bed, a truncated triangular prism (found only on 8 and
10 m/m watchmakers lathes); and the continental D-style bar bed
(used on both 6 mm and 8 mm lathes by firms such as Lorch and
Star). Other bed designs have been used, such a triangular prism
on some Boley 6.5 mm lathes, and a V-edged bed on IME's 8 mm
lathes.

Lathes that sit on a bench or table are called "bench lathes".

Lathes that do not have additional integral features for repetitive
production, but rather are used for individual part production or
modification as the primary role, are called "engine lathes".

Lathes with a very large spindle bore and a chuck on both ends
of the spindle are called "oil field lathes".

Fully automatic mechanical lathes, employing cams and gear
trains for controlled movement, are called screw machines.

Lathes that are controlled by a computer are CNC lathes.

Lathes with the spindle mounted in a vertical configuration,
instead of horizontal configuration, are called vertical lathes or
vertical boring machines. They are used where very large
diameters must be turned, and the workpiece (comparatively) is
not very long.

A lathe with a cylindrical tailstock that can rotate around a
vertical axis, so as to present different facets towards the
headstock (and the workpiece) are turret lathes.
A lathe equipped with indexing plates, profile cutters, spiral or
helical guides, etc., so as to enable ornamental turning is an
ornamental lathe.

Various combinations are possible: e.g. one could have a vertical
CNC lathe (such as a CNC VTL), etc.

Lathes can be combined with other machine tools, such as a drill
press or vertical milling machine. These are usually referred to
as combination lathes.

Major categories

Woodworking lathes




A modern woodworking lathe.

Woodworking lathes are the oldest variety. All other varieties are
descended from these simple lathes. An adjustable horizontal
metal rail - the tool rest - between the material and the operator
accommodates the positioning of shaping tools, which are
usually hand-held. With wood, it is common practice to press and
slide sandpaper against the still-spinning object after shaping to
smooth the surface made with the metal shaping tools.

There are also woodworking lathes for making bowls and plates,
which have no horizontal metal rail, as the bowl or plate needs
only to be held by one side from a metal face plate. Without this
rail, there is very little restriction to the width of the piece being
turned. Further detail can be found on the woodturning page.

Metalworking lathes
A metalworking lathe
Lathe (metal)

In a metalworking lathe, metal is removed from the workpiece
using a hardened cutting tool, which is usually fixed to a solid
moveable mounting, either a toolpost or a turret, which is then
moved against the workpiece using handwheels and/or computer
controlled motors. These (cutting) tools come in a wide range of
sizes and shapes depending upon their application. Some
common styles are diamond, round, square and triangular.

The toolpost is operated by leadscrews that can accurately
position the tool in a variety of planes. The toolpost may be
driven manually or automatically to produce the roughing and
finishing cuts required to turn the workpiece to the desired
shape and dimensions, or for cutting threads, worm gears, etc.
Cutting fluid may also be pumped to the cutting site to provide
cooling, lubrication and clearing of swarf from the workpiece.
Some lathes may be operated under control of a computer for
mass production of parts (see "Computer Numerical Control").

Manually controlled metalworking lathes are commonly provided
with a variable ratio gear train to drive the main leadscrew. This
enables different thread pitches to be cut. On some older lathes
or more affordable new lathes, the gear trains are changed by
swapping gears with various numbers of teeth onto or off of the
shafts, while more modern or expensive manually controlled
lathes have a quick change box to provide commonly used ratios
by the operation of a lever. CNC lathes use computers and
servomechanisms to regulate the rates of movement.
On manually controlled lathes, the thread pitches that can be cut
are, in some ways, determined by the pitch of the leadscrew: A
lathe with a metric leadscrew will readily cut metric threads
(including BA), while one with an imperial leadscrew will readily
cut imperial unit based threads such as BSW or UTS (UNF,UNC).
This limitation is not insurmountable, because a 127-tooth gear,
called a transposing gear, is used to translate between metric
and inch thread pitches. However, this is optional equipment that
many lathe owners do not own. It is also a larger changewheel
than the others, and on some lathes may be larger than the
changewheel mounting banjo is capable of mounting.

The workpiece may be supported between a pair of points called
centres, or it may be bolted to a faceplate or held in a chuck. A
chuck has movable jaws that can grip the workpiece securely.

There are some effects on material properties when using a
metalworking lathe. There are few chemical or physical effects,
but there are many mechanical effects, which include residual
stress, microcracks, workhardening, and tempering in hardened
materials.

Cue lathes

Cue lathes function similar to turning and spinning lathes
allowing for a perfectly radially-symmetrical cut for billiard cues.
They can also be used to refinish cues that have been worn over
the years.

Glassworking lathes

Glassworking lathes are similar in design to other lathes, but
differ markedly in how the workpiece is modified. Glassworking
lathes slowly rotate a hollow glass vessel over a fixed or variable
temperature flame. The source of the flame may be either hand-
held, or mounted to a banjo/cross slide that can be moved along
the lathe bed. The flame serves to soften the glass being worked,
so that the glass in a specific area of the workpiece becomes
malleable, and subject to forming either by inflation
("glassblowing"), or by deformation with a heat resistant tool.
Such lathes usually have two headstocks with chucks holding
the work, arranged so that they both rotate together in unison.
Air can be introduced through the headstock chuck spindle for
glassblowing. The tools to deform the glass and tubes to blow
(inflate) the glass are usually handheld.

In diamond turning, a computer-controlled lathe with a diamond-
tipped tool is used to make precision optical surfaces in glass or
other optical materials. Unlike conventional optical grinding,
complex aspheric surfaces can be machined easily. Instead of
the dovetailed ways used on the tool slide of a metal turning
lathe, the ways typically float on air bearings and the position of
the tool is measured by optical interferometry to achieve the
necessary standard of precision for optical work. The finished
work piece usually requires a small amount subsequent polishing
by conventional techniques to achieve a finished surface suitably
smooth for use in a lens, but the rough grinding time is
significantly reduced for complex lenses.

Metal spinning lathes

In metal spinning, a disk of sheet metal is held perpendicularly to
the main axis of the lathe, and tools with polished tips (spoons)
are hand held, but levered by hand against fixed posts, to
develop large amounts of torque/pressure that deform the
spinning sheet of metal.

Metal spinning lathes are almost as simple as woodturning lathes
(and, at this point, lathes being used for metal spinning almost
always are woodworking lathes). Typically, metal spinning lathes
require a user-supplied rotationally symmetric mandrel, usually
made of wood, which serves as a template onto which the
workpiece is moulded (non-symmetric shapes can be done, but it
is a very advanced technique). For example, if you want to make
a sheet metal bowl, you need a solid chunk of wood in the shape
of the bowl; if you want to make a vase, you need a solid
template of a vase, etc.
Given the advent of high speed, high pressure, industrial die
forming, metal spinning is less common now than it once was,
but still a valuable technique for producing one-off prototypes or
small batches where die forming would be uneconomical.

Ornamental turning lathes

The ornamental turning lathe was developed around the same
time as the industrial screwcutting lathe in the nineteenth
century. It was used not for making practical objects, but for
decorative work - ornamental turning. By using accessories such
as the horizontal and vertical cutting frames, eccentric chuck
and elliptical chuck, solids of extraordinary complexity may be
produced by various generative procedures.

A special purpose lathe, the Rose engine lathe is also used for
ornamental turning, in particular for engine turning, typically in
precious metals, for example to decorate pocket watch cases.
As well as a wide range of accessories, these lathes usually have
complex dividing arrangements to allow the exact rotation of the
mandrel. Cutting is usually carried out by rotating cutters, rather
than directly by the rotation of the work itself. Because of the
difficulty of polishing such work, the materials turned, such as
wood or ivory, are usually quite soft, and the cutter has to be
exceptionally sharp. The finest ornamental lathes are generally
considered to be those made by Holtzapffel around the turn of
the 19th century.

Reducing lathe

Many types of lathes can be equipped with accessory
components to allow them to reproduce an item: the original
item is mounted on one spindle, the blank is mounted on another,
and as both turn in synchronized manner, one end of an arm
"reads" the original and the other end of the arm "carves" the
duplicate.

A reducing lathe is a specialized lathe that is designed with this
feature, and which incorporates a mechanism similar to a
pantograph, so that when the "reading" end of the arm reads a
detail that measures one inch (for example), the cutting end of
the arm creates an analogous detail that is (for example) one
quarter of an inch (a 4:1 reduction, although given appropriate
machinery and appropriate settings, any reduction ratio is
possible).

Reducing lathes are used in coin-making, where a plaster original
(or an epoxy master made from the plaster original, or a copper
shelled master made from the plaster original, etc.) is duplicated
and reduced on the reducing lathe, generating a master die.

Rotary lathes

A lathe in which softwood, like spruce or pine, or hardwood, like
birch, logs are turned against a very sharp blade and peeled off in
one continuous or semi-continuous roll. Invented by Immanuel
Nobel (father of the more famous Alfred Nobel). The first such
lathes were set up in the United States in the mid-19th century.
The product is called wood veneer and it is used for finishing
chipboard objects and making plywood.

Watchmaker's lathes




Watchmakers lathes are delicate but precise metalworking
lathes, usually without provision for screwcutting, and are still
used by horologists for work such as the turning of balance
shafts. A handheld tool called a graver is often used in
preference to a slide mounted tool. The original watchmaker's
turns was a simple dead-centre lathe with a moveable rest and
two loose headstocks. The workpiece would be rotated by a bow,
typically of horsehair, wrapped around it.
Examples of lathes




Small                            Belt-driven metalworking lathe
metalworking                     in the machine shop at Hagley
                    Large old
lathe                            Museum
                    lathe

Examples of work produced from a lathe




                 Turned chess pieces
Lathe exercise

Metal lathe or metalworking lathe are generic terms for any of a
large class of lathes designed for precisely machining relatively
hard materials. They were originally designed to machine metals;
however, with the advent of plastics and other materials, and
with their inherent versatility, they are used in a wide range of
applications, and a broad range of materials. In machining
jargon, where the larger context is already understood, they are
usually simply called lathes, or else referred to by more-specific
subtype names (toolroom lathe, turret lathe, etc.). These rigid
machine tools remove material from a rotating workpiece via the
(typically linear) movements of various cutting tools, such as tool
bits and drill bits.

Construction

The machine has been greatly modified for various applications
however a familiarity with the basics shows the similarities
between types. These machines consist of, at the least, a
headstock, bed, carriage and tailstock. The better machines are
solidly constructed with broad bearing surfaces (slides or ways)
for stability and manufactured with great precision. This helps
ensure the components manufactured on the machines can meet
the required tolerances and repeatability.

Headstock




Headstock with legend, numbers and text within the description
refer to those in the image

The headstock (H1) houses the main spindle (H4), speed change
mechanism (H2,H3), and change gears (H10). The headstock is
required to be made as robust as possible due to the cutting
forces involved, which can distort a lightly built housing, and
induce harmonic vibrations that will transfer through to the
workpiece, reducing the quality of the finished workpiece.

The main spindle is generally hollow to allow long bars to extend
through to the work area, this reduces preparation and waste of
material. The spindle then runs in precision bearings and is fitted
with some means of attaching work holding devices such as
chucks or faceplates. This end of the spindle will also have an
included taper, usually morse, to allow the insertion of tapers
and centers. On older machines the spindle was directly driven
by a flat belt pulley with the lower speeds available by
manipulating the bull gear, later machines use a gear box driven
by a dedicated electric motor. The fully geared head allows the
speed selection to be done entirely through the gearbox.

Bed

The bed is a robust base that connects to the headstock and
permits the carriage and tailstock to be aligned parallel with the
axis of the spindle. This is facilitated by hardened and ground
ways which restrain the carriage and tailstock in a set track. The
carriage travels by means of a rack and pinion system,
leadscrew of accurate pitch, or feedscrew.

When a lathe is installed, the first step is to level it, which refers
to making sure the bed is not twisted or bowed. There is no need
to make the machine exactly horizontal. However, a precision
level (usually across the cross slide) can be a useful tool for
identifying and removing twist. It is advisable also to use such a
level along the bed to detect bending, in the case of a lathe with
more than four mounting points. In both instances the level is
used as a comparator rather than an absolute reference.

Types of beds include inverted "V" beds, flat beds, and
combination "V" and flat beds. "V" and combination beds are
used for precision and light duty work, while flat beds are used
for heavy duty work.

Feed and lead screws

The feedscrew (H8) is a long driveshaft that allows a series of
gears to drive the carriage mechanisms. These gears are located
in the apron of the carriage. Both the feedscrew and leadscrew
(H9) are driven by either the change gears (on the quadrant) or
an intermediate gearbox known as a quick change gearbox (H6)
or Norton gearbox. These intermediate gears allow the correct
ratio and direction to be set for cutting threads or worm gears.
Tumbler gears (operated by H5) are provided between the spindle
and gear train along with a quadrant plate that enables a gear
train of the correct ratio and direction to be introduced. This
provides a constant relationship between the number of turns the
spindle makes, to the number of turns the leadscrew makes. This
ratio allows screwthreads to be cut on the workpiece without the
aid of a die.

Some lathes have only one leadscrew that serves all carriage-
moving purposes. For screw cutting, a half nut is engaged to be
driven by the leadscrew's thread; and for general power feed, a
key engages with a keyway cut into the leadscrew to drive a
pinion along a rack that is mounted along the lathe bed.

The leadscrew will be manufactured to either imperial or metric
standards and will require a conversion ratio to be introduced to
create thread forms from a different family. To accurately
convert from one thread form to the other requires a 127-tooth
gear, or on lathes not large enough to mount one, an
approximation may be used. Multiples of 3 and 7 giving a ratio of
63:1 can be used to cut fairly loose threads. This conversion ratio
is often built into the quick change gearboxes.

Carriage




Carriage with legend, numbers and text within the description
refer to those in the image

In its simplest form the carriage holds the tool bit and moves it
longitudinally (turning) or perpendicularly (facing) under the
control of the operator. The operator moves the carriage
manually via the handwheel (5a) or automatically by engaging
the feed shaft with the carriage feed mechanism (5c). This
provides some relief for the operator as the movement of the
carriage becomes power assisted. The handwheels (2a, 3b, 5a)
on the carriage and its related slides are usually calibrated, both
for ease of use and to assist in making reproducible cuts.

Cross-slide

(3) The cross-slide stands atop the carriage and has a feedscrew
that travels perpendicular to the main spindle axis. This permits
facing operations to be performed, and the depth of cut to be
adjusted. This feedscrew can be engaged, through a gear train,
to the feed shaft (mentioned previously) to provide automated
'power feed' movement to the cross-slide. On most lathes, only
one direction can be engaged at a time as an interlock
mechanism will shut out the second gear train.

Compound rest

(2) The compound rest (or top slide) is the part of the machine
where the tool post is mounted. It provides a smaller amount of
movement along its axis via another feedscrew. The compound
rest axis can be adjusted independently of the carriage or cross-
slide. It is utilized when turning tapers, to control depth of cut
when screwcutting or precision facing, or to obtain finer feeds
(under manual control) than the feed shaft permits.

The slide rest can be traced to the fifteenth century, and in the
eighteenth century it was used on French ornamental turning
lathes. The suite of gun boring mills at the Royal Arsenal,
Woolwich, in the 1780s by the Verbruggan family also had slide
rests. The story has long circulated that Henry Maudslay
invented it, but he did not (and never claimed so). The legend
that Maudslay invented the slide rest originated with James
Nasmyth, who wrote ambiguously about it in his Remarks on the
Introduction of the Slide Principle, 1841; later writers
misunderstood, and propagated the error. Maudslay did help to
disseminate the idea widely. It is highly probable that he saw it
when he was working at the Arsenal as a boy. In 1794, whilst he
was working for Joseph Bramah, he made one, and when he had
his own workshop used it extensively in the lathes he made and
sold there. Coupled with the network of engineers he trained,
this ensured the slide rest became widely known and copied by
other lathe makers, and so diffused throughout British
engineering workshops. A practical and versatile screw-cutting
lathe incorporating the trio of leadscrew, change gears, and slide
rest was Maudslay's most important achievement.

The first fully documented, all-metal slide rest lathe was
invented by Jacques de Vaucanson around 1751. It was
described in the Encyclopédie a long time before Maudslay
invented and perfected his version. It is likely that Maudslay was
not aware of Vaucanson's work, since his first versions of the
slide rest had many errors which were not present in the
Vaucanson lathe.

Toolpost

(1) The tool bit is mounted in the toolpost which may be of the
American lantern style, traditional 4 sided square style, or in a
quick change style such as the multifix arrangement pictured.
The advantage of a quick change set-up is to allow an unlimited
number of tools to be used (up to the number of holders
available) rather than being limited to 1 tool with the lantern
style, or 3 to 4 tools with the 4 sided type. Interchangeable tool
holders allow the all the tools to be preset to a center height that
will not change, even if the holder is removed from the machine.

Tailstock
Tailstock with legend, numbers and text within the description
refer to those in the image

The tailstock is a toolholder directly mounted on the spindle
axis, opposite the headstock. The spindle (T5) does not rotate
but does travel longitudinally under the action of a leadscrew
and handwheel (T1). The spindle includes a taper to hold drill
bits, centers and other tooling. The tailstock can be positioned
along the bed and clamped (T6) in position as required. There is
also provision to offset the tailstock (T4) from the spindles axis,
this is useful for turning small tapers.

The image shows a reduction gear box (T2) between the
handwheel and spindle, this is a feature found only in the larger
center lathes, where large drills may necessitate the extra
leverage.




Types of metal lathes

There are many variants of lathes within the metalworking field.
Some variations are not all that obvious, and others are more a
niche area. For example, a centering lathe is a dual head
machine where the work remains fixed and the heads move
towards the workpiece and machine a center drill hole into each
end. The resulting workpiece may then be used "between
centers" in another operation. The usage of the term metal lathe
may also be considered somewhat outdated these days, plastics
and other composite materials are in wide use and with
appropriate modifications, the same principles and techniques
may be applied to their machining as that used for metal.

Center lathe / engine lathe / bench lathe




Two-speed back gears in a cone-head lathe.




A typical center lathe.

The terms center lathe, engine lathe, and bench lathe all refer to
a basic type of lathe that may be considered the archetypical
class of metalworking lathe most often used by the general
machinist or machining hobbyist. The name bench lathe implies a
version of this class small enough to be mounted on a workbench
(but still full-featured, and larger than mini-lathes or micro-
lathes). The construction of a center lathe is detailed above, but
depending on the year of manufacture, size, price range, or
desired features, even these lathes can vary widely between
models.
Engine lathe is the name applied to a traditional late-19th-
century or 20th-century lathe with automatic feed to the cutting
tool, as opposed to early lathes which were used with hand-held
tools, or lathes with manual feed only. The usage of "engine"
here is in the mechanical-device sense, not the prime-mover
sense, as in the steam engines which were the standard
industrial power source for many years. The works would have
one large steam engine which would provide power to all the
machines via a line shaft system of belts. Therefore early engine
lathes were generally 'cone heads', in that the spindle usually
had attached to it a multi-step pulley called a cone pulley
designed to accept a flat belt. Different spindle speeds could be
obtained by moving the flat belt to different steps on the cone
pulley. Cone-head lathes usually had a countershaft (layshaft) on
the back side of the cone which could be engaged to provide a
lower set of speeds than was obtainable by direct belt drive.
These gears were called back gears. Larger lathes sometimes
had two-speed back gears which could be shifted to provide a
still lower set of speeds.

When electric motors started to become common in the early
20th century, many cone-head lathes were converted to electric
power. At the same time the state of the art in gear and bearing
practice was advancing to the point that manufacturers began to
make fully geared headstocks, using gearboxes analogous to
automobile transmissions to obtain various spindle speeds and
feed rates while transmitting the higher amounts of power
needed to take full advantage of high speed steel tools.

The inexpensive availability of electronics has again changed the
way speed control may be applied by allowing continuously
variable motor speed from the maximum down to almost zero
RPM. (This had been tried in the late 19th century but was not
found satisfactory at the time. Subsequent improvements have
made it viable again.)

Toolroom lathe
A toolroom lathe is a lathe optimized for toolroom work. It is
essentially just a top-of-the-line center lathe, with all of the best
optional features that may be omitted from less expensive
models, such as a collet closer, taper attachment, and others.
There has also been an implication over the years of selective
assembly and extra fitting, with every care taken in the building
of a toolroom model to make it the smoothest-running, most-
accurate version of the machine that can be built. However,
within one brand, the quality difference between a regular model
and its corresponding toolroom model depends on the builder and
in some cases has been partly marketing psychology. For name-
brand machine tool builders who made only high-quality tools,
there wasn't necessarily any lack of quality in the base-model
product for the "luxury model" to improve upon. In other cases,
especially when comparing different brands, the quality
differential between (1) an entry-level center lathe built to
compete on price, and (2) a toolroom lathe meant to compete
only on quality and not on price, can be objectively demonstrated
by measuring TIR, vibration, etc. In any case, because of their
fully-ticked-off option list and (real or implied) higher quality,
toolroom lathes are more expensive than entry-level center
lathes.

Turret lathe and capstan lathe

Turret lathe

Turret lathes and capstan lathes are members of a class of
lathes that are used for repetitive production of duplicate parts
(which by the nature of their cutting process are usually
interchangeable). It evolved from earlier lathes with the addition
of the turret, which is an indexable toolholder that allows
multiple cutting operations to be performed, each with a different
cutting tool, in easy, rapid succession, with no need for the
operator to perform setup tasks in between (such as installing or
uninstalling tools) nor to control the toolpath. (The latter is due
to the toolpath's being controlled by the machine, either in jig-
like fashion [via the mechanical limits placed on it by the turret's
slide and stops] or via IT-directed servomechanisms [on CNC
lathes].)

There is a tremendous variety of turret lathe and capstan lathe
designs, reflecting the variety of work that they do.

Gang-tool lathe

A gang-tool lathe is one that has a row of tools set up on its
cross-slide, which is long and flat and is similar to a milling
machine table. The idea is essentially the same as with turret
lathes: to set up multiple tools and then easily index between
them for each part-cutting cycle. Instead of being rotary like a
turret, the indexable tool group is linear.

Multispindle lathe

screw machine

Multispindle lathes have more than one spindle and automated
control (whether via cams or CNC). They are production
machines specializing in high-volume production. The smaller
types are usually called screw machines, while the larger
variants are usually called automatic chucking machines,
automatic chuckers, or simply chuckers. Screw machines usually
work from bar stock, while chuckers automatically chuck up
individual blanks from a magazine. Typical minimum profitable
production lot size on a screw machine is in the thousands of
parts due to the large setup time. Once set up, a screw machine
can rapidly and efficiently produce thousands of parts on a
continuous basis with high accuracy, low cycle time, and very
little human intervention. (The latter two points drive down the
unit cost per interchangeable part much lower than could be
achieved without these machines.)

Rotary transfer machines might also be included under the
category of multispindle lathes, although they defy traditional
classification. They are large, expensive, modular machine tools
with many CNC axes that combine the capabilities of lathes,
milling machines, and pallet changers.

CNC lathe / CNC turning center




CNC lathe with milling capabilities




An example turned vase and view of the tool turret

CNC lathes are rapidly replacing the older production lathes
(multispindle, etc) due to their ease of setting and operation.
They are designed to use modern carbide tooling and fully utilize
modern processes. The part may be designed and the toolpaths
programmed by the CAD/CAM process, and the resulting file
uploaded to the machine, and once set and trialled the machine
will continue to turn out parts under the occasional supervision
of an operator.

The machine is controlled electronically via a computer menu
style interface, the program may be modified and displayed at
the machine, along with a simulated view of the process. The
setter/operator needs a high level of skill to perform the process,
however the knowledge base is broader compared to the older
production machines where intimate knowledge of each machine
was considered essential. These machines are often set and
operated by the same person, where the operator will supervise
a small number of machines (cell).

The design of a CNC lathe has evolved yet again however the
basic principles and parts are still recognizable, the turret holds
the tools and indexes them as needed. The machines are often
totally enclosed, due in large part to Occupational health and
safety (OH&S) issues.

With the advent of cheap computers, free operating systems
such as Linux, and open source CNC software, the entry price of
CNC machines has plummeted. For example, Sherline makes a
desktop CNC lathe that is affordable by hobbyists.

Swiss-style lathe / Swiss turning center

For work requiring extreme accuracy (sometimes holding
tolerances as small as a few tenths of a thousandth of an inch), a
Swiss-style lathe is often used. A Swiss-style lathe holds the
workpiece with both a collet and a guide bushing. The collet sits
behind the guide bushing, and the tools sit in front of the guide
bushing, holding stationary on the Z axis. To cut lengthwise
along the part, the tools will move in and the material itself will
move back and forth along the Z axis. This allows all the work to
be done on the material near the guide bushing where it's more
rigid, making them ideal for working on slender workpieces as
the part is held firmly with little chance of deflection or vibration
occurring.

This style of lathe is also available with CNC controllers to
further increase its versatility.

Most CNC Swiss-style lathes today utilize two spindles. The main
spindle is used with the guide bushing for the main machining
operations. The secondary spindle is located behind the part,
aligned on the Z axis. In simple operation it picks up the part as
it is cut off (aka parted off) and accepts it for second operations,
then ejects it into a bin, eliminating the need to have an operator
manually change each part, as is often the case with standard
CNC turning centers. This makes them very efficient, as these
machines are capable of fast cycle times, producing simple parts
in one cycle (i.e. no need for a second machine to finish the part
with second operations), in as little as 10-15 seconds. This
makes them ideal for large production runs of small-diameter
parts.

Combination lathe / 3-in-1 machine

A combination lathe, often known as a 3-in-1 machine, introduces
drilling or milling operations into the design of the lathe. These
machines have a milling column rising up above the lathe bed,
and they utilize the carriage and topslide as the X and Y axes for
the milling column. The 3-in-1 name comes from the idea of
having a lathe, milling machine, and drill press all in one
affordable machine tool. These are exclusive to the hobbyist and
MRO markets, as they inevitably involve compromises in size,
features, rigidity, and precision in order to remain affordable.
Nevertheless, they meet the demand of their niche quite well,
and are capable of high accuracy given enough time and skill.
They may be found in smaller, non-machine-oriented businesses
where the occasional small part must be machined, especially
where the exacting tolerances of expensive toolroom machines,
besides being unaffordable, would be overkill for the application
anyway from an engineering perspective.

Mini-lathe and micro-lathe

Mini-lathes and micro-lathes are miniature versions of a general-
purpose center lathe (engine lathe). They typically have swings
in the range of 3" to 7" (70 mm to 170 mm) diameter (in other
words, 1.5" to 3.5" (30 mm to 80 mm) radius). They are small and
affordable lathes for the home workshop or MRO shop. The same
advantages and disadvantages apply to these machines as
explained earlier regarding 3-in-1 machines.
As found elsewhere in English-language orthography, there is
variation in the styling of the prefixes in these machines' names.
They are alternately styled as mini lathe, minilathe, and mini-
lathe and as micro lathe, microlathe, and micro-lathe.

Wheel lathe

A lathe for turning the wheels of railway locomotives and rolling
stock

Brake lathe

A lathe specialized for the task of resurfacing brake drums and
discs in automotive or truck garages.

Screw-cutting lathe

A screw-cutting lathe is a machine (specifically, a lathe) capable
of cutting very accurate screw threads via single-point screw-
cutting, which is the process of guiding the linear motion of the
tool bit in a precisely known ratio to the rotating motion of the
workpiece. This is accomplished by gearing the leadscrew
(which drives the tool bit's movement) to the spindle with a
certain gear ratio for each thread pitch. Every degree of spindle
rotation is matched by a certain distance of linear tool travel,
depending on the desired thread pitch (English or metric, fine or
course, etc.). Until the early 19th century, the notion of a screw-
cutting lathe stood in contrast to the notion of a regular lathe,
which lacked the parts needed to guide the cutting tool in the
precise path needed to produce an accurate thread. Since the
early 19th century, it has been common practice to build these
parts into any general-purpose metalworking lathe; thus, the
dichotomy of "regular lathe" and "screw-cutting lathe" does not
apply to the classification of modern lathes. Instead, there are
other categories, some of which bundle single-point screw-
cutting capability among other capabilities (for example, regular
lathes, toolroom lathes, and CNC lathes), and some of which omit
single-point screw-cutting capability as irrelevant to the
machines' intended purposes (for example, speed lathes and
turret lathes).

Today the threads of threaded fasteners (such as machine
screws, wood screws, wallboard screws, and sheetmetal
screws) are not cut via single-point screw-cutting; instead they
are generated by other, faster processes, such as deformation
between forming dies and cutting within thread dies. The latter
process is the one employed in modern screw machines. These
machines, although they are lathes specialized for making
screws, are not screw-cutting lathes in the sense of employing
single-point screw-cutting.

History

The screw has been known for millennia. Archimedes devised the
water screw, a system for raising water. Screws as mechanical
fasteners date to the first century BCE. Although screws were
tremendously useful, the difficulty in making them prevented any
widespread adoption.

Early machine screws were made by hand, with files used to cut
the threads. This made the screw slow and expensive to make
and the quality highly dependent on the skill of the maker. A
process for automating the manufacture of screws and improving
the accuracy and consistency of the thread was needed.

Lathes have been around since ancient times. Adapting them to
screw-cutting is an obvious choice, but the problem of how to
guide the cutting tool through the correct path was an obstacle
for many centuries. Very old lathes used a mechanism that
provided for back-and-forth motion, which rotated the workpiece
first one way and then the other. Leonardo da Vinci created
drawings showing screw-cutting machines that did away with
this back-and-forth system and replaced it with a system that
maintained rotation in one direction. He also added a flywheel to
keep the rotation consistent. His design also used two
leadscrews to guide the tool, perhaps to average out the error in
the leadscrew construction. It is unknown whether this machine
was ever built, but it is an example of Leonardo's genius.

Dozens of designs followed but few were significantly accurate.
Henry Hindley designed and constructed a screw-cutting lathe
circa 1739. It featured a plate guiding the tool and power
supplied by a hand-cranked series of gears. By changing the
gears, he could cut screws with different pitch. Removing a gear
permitted him to make left-handed threads.[1].

The first truly modern screw-cutting lathe was likely constructed
by Jesse Ramsden in 1775. He appears to have been the first
person to put a leadscrew into actual use (although, as
Leonardo's drawings show, he was not the first person ever to
think of the idea), and he was the first to use diamond-tipped
cutting tools.[2] His device also included a slide rest and change
gear mechanism. These form the elements of a modern (non-
CNC) lathe and are in use to this day. Ramsden was able to use
his first screw-cutting lathe to make even more accurate lathes.
With these, he was able to make an exceptionally accurate
dividing engine and in turn, some of the finest astronomical,
surveying, and navigational instruments of the 18th century.

Others followed. Senot, in 1795, created a screw-cutting lathe
capable of industrial-level production. David Wilkinson of
Vermont employed a slide-rest in 1798. However, these inventors
were soon overshadowed by Henry Maudslay, who in 1800
created a screw-cutting lathe that is frequently cited as the first.
Clearly, his was not the first; however, his did become the best
known, spreading to the rest of the world the winning
combination of leadscrew, slide-rest, and change gears. These
late-18th-century screw-cutting lathes represented the
breakthrough development of the technology. They permitted the
large-scale, industrial production of screws that were
interchangeable. Standardization of threadforms (including
thread angle, pitches, major diameters, pitch diameters, etc.)
began immediately on the intra-company level, and by the end of
the 19th century, it had been carried to the international level
(although pluralities of standards still exist).

				
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