Lathe Parts

- being a brief description of the names and functions of

parts -
The names given to various parts of the lathe have changed over the years -
and are still not completely standardised. No doubt when the government
has finished organising every other aspect of our lives it will appoint a
highly-paid commission to look into the matter and make
"recommendations".
If you would like to buy a book or CD to extend your knowledge of lathes -
and how to operate them - look on the home page and here.
Illustrations of the parts discussed can be found by following the various
hyperlinks and also at the bottom of this page. It may be that an Instruction
Manual, an Illustrated Parts Book or informative sales Literature may be
available for your lathe: you can check by clicking here.

BED
The bed of the lathe provides the foundation for the whole machine and
holds the headstock, tailstock and carriage in alignment. The surfaces of the
bed that are finely machined - and upon which the carriage and tailstock
slide - are known as "ways".
Some beds have a gap near the headstock to allow extra-large diameters to
be turned. Sometimes the gap is formed by the machined ways stopping
short of the headstock, sometimes by a piece of bed that can be unbolted,
removed and lost.
Some very large lathes have a "sliding bed" where the upper part, on which
the carriage and tailstock sit, can be slid along a lower separate part - and so
make the gap correspondingly larger or smaller.

SADDLE
The casting that fits onto the top of the bed and slides along it is known,
almost universally, as the "Saddle" - a self-explanatory and very suitable
term.

APRON
The vertical, often flat and rectangular "plate" fastened to the front of the
"Saddle" is known as the "Apron" and carries a selection of gears and
controls that allow the carriage to be power driven up and down the bed -
and also engage the screwcutting feed and various powered tool feeds,
should they be fitted. The leadscrew, and sometimes a power shaft, usually
pass through the apron and provide it with a drive for the various functions it
has to perform. The sophistication of the apron-mounted controls and their
ease of use is a reliable indication of the quality of a lathe. Virtually all
screw-cutting lathes have what is commonly-called a "half-nut" lever that
closed down one and sometimes two halves of a split nut to grasp the
leadscrew and provide a drive for screwcutting and sometimes power feeds
was well.
Apron design can be roughly divided into "single-wall" and "double-wall"
types. The "single-wall" apron has just one thickness of metal and,
protruding from it (and unsupported on their outer ends) are studs that carry
gears. The "double-wall" apron is a much more robust structure, rather like a
narrow, open-topped box with the gear-carrying studs fitted between the two
walls - and hence rigidly supported at both ends. This type of construction
produces a very stiff structure - and one that is far less likely to deflect under
heavy-duty work; another advantage is that the closed base of the "box" can
be used to house an oil reservoir the lubricant from which can be pumped to
supply the spindles, gears and even, on some lathes, the sliding surfaces of
the bed and cross slide.

CROSS SLIDE and TOP SLIDE

Sitting on top of the "Saddle" is the "Cross Slide" - that, as its name implies,
moves across the bed - and on top of that there is often a "Top Slide" or
"Tool Slide" that is invariably arranged so that it can be swivelled and
locked into a new position.
Very early lathes had a simple T-shaped piece of metal against which the
turner "rested" his tool (all turning being done by hand) but when it became
possible to move this "Rest" across the bed by a screw feed it became
known, appropriately enough, as a "Slide-rest". The earliest known example
of a "Slide-rest" is illustrated in Mittelalterliche Hausbuch, a German
publication of about 1480.
After the "Top Slide" became a more common fitting the term "Slide-rest"
was not so frequently used - and the different functions of the two slides led
to their specific names being more widely adopted.
When two slides are provided (or sometimes, on watchmaker's lathes, three)
the complete assembly is known as a "Compound" or "Compound Slide" or
even "Compound Slide-rest". Some makers label the "Top Slide" as the
"Compound Rest" or even the "Compound Slide" - but as "to compound"
means the 'joining of two or more' - not 'one' - so this is not a correct use of
the term.

CARRIAGE
The whole assembly of Saddle, Apron, Top and Cross Slide is known as the
"Carriage". Some American publications (even makers' handbooks) have
been known to casually refer to the "Saddle" as the "Carriage" - but this
incorrect.

HEADSTOCK.
The lathe Headstock used, at one time, to be called the "Fixed Headstock" or
"Fixed Head", and the rotating shaft within it the "Mandrel". Today the
mandrel is usually called the "Spindle", but this can cause confusion with
the tailstock, where the sliding bar is known variously as the "ram", "barrel"
- and "spindle".
The headstock is normally mounted rigidly to the bed (exceptions exist in
some production and CNC lathes) and holds all the mechanisms, including
various kinds and combinations of pulleys or gears, so that the spindle can
be made to turn at different speeds.

HEADSTOCK SPINDLE
The end of the headstock spindle is usually machined so that it can carry a
faceplate, chuck, drive-plate, internal or external collets - or even special
attachments designed for particular jobs. In turn, these attachments hold the
workpiece that is going to be machined.
The "fitting" formed on the end of the spindle is normally one of four types:
- a simple flange through which threaded studs on a faceplate or chuck
(for example) can pass and be tightened into place with nuts. This is a secure
method, and allows high-speed reverse, but is very inconvenient on a
general-purpose lathe.
- A threaded nose onto which fittings screw. This is perfectly acceptable
for smaller lathes, but unsatisfactory on larger industrial machines where,
for reasons of production economy, the spindle may need to be reversed at
high speed. Reversing a screwed-on chuck causes it to unscrew - with
potentially disastrous results.
- A "D1-taper Camlock" fitting - a long-used, standard system that
employs three or more "studs" that are turned to lock into the back of chucks
and faceplates, etc.
- A "taper-nose, long-key drive" - an older but excellent American
design where a large screwed ring was held captive on the end of the spindle
and used to draw the chuck, or other fitting, onto a long, keyed taper formed
on the spindle end. An ideal system for the rigid mounting of heavier
chucks, it has now largely fallen into disuse. The fitting was available in
various sizes starting at L00 (L zero zero) and worked up through L0, L1,
L2, etc.
- various fittings that became increasingly complex and apparently
invented for the sake of being able to claim a National Standard (the famous
Not-Invented-Here syndrome). All these succeeded in doing was to raise
manufacturing costs by preventing the interchange of spindle-nose tooling
between machines and requiring firms to keep larger inventories of spares.
Some of these included: British and ISO Standard Spindle Noses - Direct
Mounting; British & ISO Short Taper with Bolt or Stud Fixing; British &
ISO Short Taper with Camlock Fixing; British & ISO Short Taper with
Bayonet Ring Fixing and, of course, German Standard Spindle Noses.
Unbelievably there appears never to have been a French standard - and we
still await official announcement of the rumoured Botswana-Standard
Triple-cam, Over-locking nose and Chinese New Moon Slide-and-Snap
fittings.

BACKGEAR
As its name implies, "backgear" is a gear mounted at the back of the
headstock (although in practice it is often located in other positions) that
allows the chuck to rotate slowly with greatly-increased torque (turning
power). At first, the ability to run a workpiece slowly might seem
unnecessary, but a large-diameter casting, fastened to the faceplate and run
at 200 rpm (about the slowest speed normally available on a lathe without
backgear) would have a linear speed at its outer edge beyond the turning
capacity of a small lathe. By engaging backgear, and so reducing the speed
but increasing the torque, even the largest faceplate-mounted jobs can be
turned successfully.
Screwcutting also requires slow speeds, typically between 25 and 50 rpm -
especially if the operator is a beginner, or the job tricky. A bottom speed in
excess of those figures (as usually found on most Far Eastern and European
machines but not those built in the United Kingdom) means that
screwcutting - especially internally, into blind holes - is, in effect,
impossible. These lathes are advertised as "screwcutting" but what that
means in reality is just power feed along the bed. Even if you go to the
trouble of making up a pulley system to reduce the spindle speeds you will
find the torque needed to turn large diameters at low speeds causes the belts
to slip. The only solution is a gear-driven low speed and so a proper small
lathe, with a backgear fitted, not only becomes capable of cutting threads but
can also tackle heavy-duty drilling, big-hole boring and large-diameter
facing: in other words, it is possible to use it to the very limits of its capacity
and strength.
Beginners are sometimes confused about how to engage backgear -
especially if the lathe lacks a handbook - but with a little care anyone can
work out how it should be done, at least on a conventional machine. On the
main spindle of the lathe, the one carrying the drive pulley, will be found a
large gear, generally referred to as the "Bull Wheel". The Bull Wheel is
attached to the pulley by a nut and bolt, a spring-loaded pin, a pawl that
presses into a gear on the pulley (or some other means) and, if this fastening
is undone - by slackening the nut and pushing it towards the pulley, or by
pulling the pin out - it should be found that the pulley will spin freely on the
shaft. By moving the "backgears" into position - they generally slide
sideways, or are mounted on an eccentric pin - the mechanism will come
into operation. If the pulley will not spin on the shaft, or there seems to be
no obvious way of disconnecting the Bull Wheel from the pulley, it may be
that you are dealing with an "over-engineered" machine where some clever
device has been introduced to make life "easy" for the operator. Sometimes
there will be a screw, flush with the surface of the drive pulley and beneath
this a spring-loaded pin that pushes into the back face of the Bull Wheel.
Quick-action "Sliding-cam" mechanisms are occasionally used (as on the
Drummond and Myford M Series lathes) where a knob on the face of the
Bull Wheel has to be pushed sideways, and so ride up a ramp, which action
disengages the connecting pin automatically. Some lathes, with enclosed
headstocks (like later Boxford models) have a "single-lever" backgear; in
this system moving the first part of the lever's movement disengages the
connection whilst the next brings the backgear into mesh.

LEADSCREW
Originally termed a "master thread", or described as the "leading screw", but
now always referred to as the "leadscrew", this is a long threaded rod
normally found running along the front of the bed or, on some early
examples running between the bed ways down the bed's centre line. By
using a train of gears to connect the lathe spindle to the leadscrew - and the
leadscrew to the lathe carriage - the latter, together with its cutting tool,
could be forced to move a set distance for every revolution of the spindle.

TAILSTOCK
The Tailstock was once known in England as the "Loose headstock", "
Poppet head" or "Loose head" - the latter old-fashioned term being used by
Harrison and other English firms in some of their advertising literature until
the early 1970s. The unit is arranged to slide along the bed and can be
locked to it at any convenient point; the upper portion of the unit is fitted
with what is variously called a "barrel", "spindle" "ram" or "shoot" that can
be moved in and out of the main casting by hand, lever or screw feed and
carries a "Dead Centre" that supports the other end of work held (by various
means) in the headstock.
Special centres, which rotate with the work, can be used in the tailstock ;
these are known as "Rotating Centres" and should not be referred to as "live
centres" - that term being reserved for the centre carried in the headstock
spindle.
Long ago centres were referred to by turners as "Poppets" - presumably
from "pop it in" - and they carried their own with them, secured in cotton
waste and jealously guarded in the top pocket of their overalls.

COUNTERSHAFT
Most small electric motors in Britain spin at 1425 rpm, whilst those in the
USA and Europe are usually marked a little faster at 1600 to 1700 rpm or so.

If the lathe spindle was to be driven directly from one of these motors, even
using a small pulley on the motor shaft, and a larger one on the lathe, it
would be turning far too quickly to be useful for the great majority of jobs;
hence, it is necessary to introduce some way of reducing the lathe's spindle
speed - and that is the job of the countershaft.
In a typical arrangement, illustrated here, the motor is fastened to an upright,
hinged, cast-iron plate and fitted with a small pulley on its spindle. Because
the 1500 rpm motor is driving a much larger pulley in a ratio of something
like 5 : 1 - the speed is reduced to 300 rpm (1500 divided by 5).
On the same shaft as the very large pulley is a set of three smaller pulleys,
arranged in the "reverse" order from those on the lathe. If the middle pulley
on the countershaft is made to drive the identically-sized pulley on the lathe
spindle that too, of course, will turn at 300 rpm. The pulleys each side of it
are normally arranged to halve and double that speed - hence the creation of
a speed set covering a useful 150 rpm, 300 rpm and 600 rpm.
It is a simple matter to fit both a small and a large pulleys to the motor shaft,
and two correspondingly larger pulleys on the countershaft, and so double
the number of available speeds to six. If a two-speed electric motor is used
the range doubles again to 12 and, should the lathe designer have managed
to squeeze a four-step pulley between the spindle bearings, a total of 16
would be available; with a backgear fitted the total would rise to thirty-two
speeds that, typically, might start at 25 rpm and extend all the way up to
over 3000 rpm.

CHANGEWHEELS and TUMBLE REVERSE

These are the gears that take the drive from the headstock spindle down to
the leadscrew. They are normally contained within a cover at the extreme
left-hand side of the lathe - but many older lathes, built in times when
manufacturers were not concerned with saving people from themselves, left
them exposed.
The gears are called "changewheels" because of the necessity to change
them every time a different thread, or rate of tool feed, was required and the
expression goes back to the earliest time that gears were used for this
purpose. The gear train is usually carried on a "quadrant arm" able to be
adjusted by being swung on its mounting to allow the mesh of the topmost
gear with the output gear on the spindle or tumble reverse mechanism to be
set. In Great Britain the arm is sometimes called the "Banjo" - although this
expression should really be limited to those with just one slot. Some
manufacturers, to make life difficult for themselves and their customers,
tried other systems as well. A drive through changewheels often
incorporates a "tumble-reverse" mechanism by which means the drive to the
leadscrew can be instantly reversed and hence the cutting tool made to move
towards or away from the headstock at will. In its "neutral" position it also
allows the headstock spindle to rotate freely and quietly without having to
drive the screwcutting changewheels and leadscrew.

For more details of screwcutting, click here and for a further explanation of
the features required on a small here.

SCREWCUTTING - and fine feeds - in the

LATHE

The mechanical generation of threads is essentially a very

simple process and the following article outlines the basic
principles - but does not attempt to cover the details, as already
published many times.
A book with screwcutting information most suitable for the
amateur (and ideal to refresh the memory of the professional) is
"The Amateurs Lathe". This gives a complete breakdown of the
process with simple-to-follow instructions that will enable even
the complete beginner to cut threads successfully. Another
useful publication with complete instructions about how to
arrange lathe changewheels to generate any thread pitch is
"Screwcutting in the Lathe"
A set of gear-train calculators for use with changewheel and
gearbox-equipped lathes, together with instructions, can also be
found here .
Threads are not an invention of the recent mechanical age: Hero
of Alexander had devised a method of generating larger ones
two thousand or more years ago - and for centuries cabinet and
clock makers had been making their own by hand. However,
starting with the Industrial Revolution, and continuing through
Victorian times, a need arose as never before for nuts, bolts and
threaded fittings in a bewildering variety of types and sizes. The
situation today, following decades of research into a wide range
of sometimes-conflicting requirements, and the standardisation
to metric measures (except in the USA) is a huge number of
thread types and hundreds of different designs of "fastener".
However, despite this apparent complexity, the essential
elements of threading on a lathe are simple. For thousands of
years the lathe had been, in essence, a potter's wheel turned on
its side and capable, in engineering terms, of only the simplest
work. Its first use for screwcutting was nothing short of a
revolutionary step for, by using a train of gears to connect the
lathe spindle to a long screw running along the length of the bed
- and the screw to the lathe carriage - the latter, together with its
cutting tool, could be forced to move a set distance for every
revolution of the spindle. If the workpiece revolved eight times
and the cutting tool was arranged, by the gearing, to move one
inch, then a spiral would be cut with 8 turns per inch - or 8 t.p.i.
(t.p.i. = threads per inch).
The long threaded rod along the bed
was originally termed a master thread
or leading screw, but is now generally
referred to as the leadscrew. Any
leadscrew needs to be very accurately
made (they are often produced by
specialist manufacturers, not the
 Whitworth thread form with machine-tool builders themselves)
55 degree angle and with an Acme, square or other thread
rounded roots and crests. form optimised for the task - but never
Other threads have flat with a standard Whitworth or Metric
crests with rounded roots, form - as unfortunately found on many
or visa- versa, or both crest cheaper lathes from the Far East. The
and root can be flat. The leadscrew will reproduce its exact
angle can also differ - pitch (hence the need for accuracy) on
standard metric threads are the material to be threaded - providing
60 degrees - whilst some it can be driven directly in some way
threads are "square cut" at from the headstock spindle - usually
90 degrees. Whilst the by ordinary straight-cut gears but
"single point" tool occasionally by bevel gears, epicyclic
commonly used in a lathe drives or even, in a few cases, using
can cut the angles toothed belts (of course, with the
correctly, it cannot advent of computer control, the
generate the radii at root relative movements of spindle and
and crest - and these are carriage are easily controlled by a
sometimes formed in the program - hence, it's now possible to
post-machining stage by generate threads with no need for any
the use of a hard steel physical connection between spindle
"chaser". and carriage).
A side benefit of screwcutting was the
realisation that an automatic, steady
feed along the bed produced a much
improved surface finish, especially if
the feed was slow and the tool
correctly shaped. Thus, for everyday-
use the changewheels are normally
arranged to provide a very fine feed to
the carriage; to set them for
screwcutting means removing most or
all of them and building up as fresh
train following the instructions on a
"screwcutting chart" that should be
attached to the machine. At the end of
the threading job the screwcutting
train is removed and the fine-feed
Basic form of the single- gears replaced. This time-wasting
point threading tool used to work can be largely avoided if a
cut external threads. screwcutting gearbox is fitted - hence
their popularity in industry. However,
not even a full "quick-change"
screwcutting gearbox can generate
every pitch of thread and it is
sometimes necessary to substitute
changewheels in order to extend the
range of the box - or generate metric
threads from an English gearbox, or
visa versa. Despite the attractions of a
screwcutting gearbox for amateur use
(quick and simple gear selection) as
saving time is not usually as
consideration a lathe fitted with
changewheels provides a much more
 adaptable machine.
If the lathe's changewheel chart is
missing, all is not lost, the book,
Screwcutting in the Lathe will help to
calculate a fresh set. Further help can
be found in a set of instructions for
using changewheel calculators, and the
necessary program downloads, can be
found here.
Driving the cutting tools by a direct
mechanical connection with the
An essential part of the headstock also allowed, in ordinary
screwcutting toolkit - a work, a much smoother and more
threading gauge marked consistent finish - and at the same time
with the common thread greatly reduced the fatigue suffered by
angles. This allows the tool the operator. This form of powered
to be set "square" to the motion was originally called self-
work, as illustrated below. acting or self-act - and both terms
were once widely used to distinguish
between plain-turning and
screwcutting lathes.
When the carriage is connected to the
leadscrew some form of "nut" is used:
this can be either solid and
permanently engaged or either a single
or double "clasp nut" that the operator
can engaged and disengage at will.
However, once the "clasp nuts" have
been opened, and the carriage moved
back to allow another cut to be taken,
the problem arises of how to re-engage
the nuts at the correct point--a problem
solved by a simple but ingenious
device, the "Dial Thread Indicator".
Using a thread The DTI consists of a gear engaged
gauge to set up for with the leadscrew but mounted on a
external shaft with a dial plate at the other end
threading. engraved with lines so that the
operator, by following charts (that
vary with the pitch of thread being
 cut), can safely engage the nuts and
continue threading accurately.
Unfortunately, an interesting difficulty
arises when cutting metric pitch
threads on an English lathe - or vice
versa - the leadscrew nuts must not be
disengaged and the lathe has to be
"electrically reversed" back to a start
point each time a new cut is taken.
Different Threads:
The first question that springs to the
mind of the novice is: "Will my lathe
be able to cut different types of
thread?" (Whitworth, British
Standard Fine, American National
Coarse, British Standard Brass,
Using a thread gauge American National Fine, British
to set the tool for Standard Brass, Unified National
internal threading. The Coarse, Unified National Fine, British
gauge is held against a Association, British Cycle Standard,
plate pressed against Metric, etc.) The answer is, yes.
the accurately turned Providing the lathe has the
end of the tube which is changewheels necessary to gear the
to be threaded. spindle to the headstock so that the
tool moves the right distance whilst
the spindle revolves once - it can be
done. The 'form' or "shape" of the
thread (which, simply put, is what
makes the essential difference between
the "types" of thread, not their pitch) is
entirely in the 'shape' of the tool (or
tools) used to cut it. The tool can be
ground to replicate any thread angle at
will; if you wished, for example, you
The could even invent your own; first
cutting however check this link or this one:
edge of they list and explain many of the
an threads forms both current and
external obsolete. Of course, not all is quite so
chaser. simple, and at the end of this
introductory article is a simple
explanation of one of the confusing
differences between metric and Inch
threads.
A History Lesson:
The two engineers most closely
associated with the development of
mechanically-developed screw threads
(although they did not invent the
process) were both active in the 1800s:
Henry Maudsley (1771 - 1831)
"Machine Builder" of London,
England (the "engineer's engineer")
and one of his apprentices, Joseph
Whitworth (1803 - 1887) Toolmaker
 of Manchester, England known for his
plain-speaking not to say blunt ways
(and probably the epitome of Shaw's
dictum that "all progress depends on
the unreasonable man."). Maudslay
was the first able to make, and exploit,
a very accurate screw thread. His
masterpiece was a screw five feet long
and two inches in diameter (1525 mm
A thread chaser for by 51 mm) with fifty turns per inch
internal work (50 per 25 mm) on which ran a nut
twelve inches (305 mm) long with 600
threads. The apparatus was designed
to average out pitch errors over small
distances and was a vital element in
the process of engraving the scale
markings on astronomical and other
very accurate measuring devices.
Maudslay went on to manufacture a
range of screwcutting lathes (using the
principle of a "master thread" or
"leading screw") examples of which
can be seen in the London Science
Museum and the Henry Ford Museum
in Dearborn, Michigan, USA.
Astoundingly, so accurate were
Maudslay's threads (and so precise his
measuring equipment). that he was
able to observe the expansion effect of
sunlight falling across one end of a
leadscrew.
Whitworth was an inventor, toolmaker
and designer (and millionaire
businessman) who brought a
disciplined approach to engineering.
His design and development skills
ranged across almost the whole field
of mechanics but, following the
publication in 1841 of his: "On a
Universal System of Screw Threads"
he is best remembered for his success
in standardising what was, at the time,
a chaotic system of hand-fitted, non-
interchangeable screwed fittings. He
collected a large sample of nuts and
bolts from a variety of workshops and,
having examined their properties,
proposed a system whereby the ratio
between the depth of the thread and its
pitch was maintained over a range of
sizes - and that the angle of the thread
be 55 degrees. The system was in use
in his own workshops by 1858 and
was quickly taken up by other
engineers as its benefits of simplicity
and interchangeability - to say nothing
 of its recommendation by the greatest
living British engineer of the day -
became obvious.

Forming Threads by Hand:

It is possible to generate threads on a
revolving cylindrical surface without
using mechanical assistance by
employing a "chaser". These look
rather like wood-turning chisels with a
"thread form" cut into their end or side
faces and are made from hard steel -
tool steel for the finest-quality ones -
and vary in width and thickness
according to their thread pitch and job
they have to do.
The full-sized type are normally fitted
to stout wooden handles to give the
necessary purchase (which can be
considerable) and are expensive.
However, there is a cheaper
alternative, the chasers that come from
automatically-releasing
With skill (and luck for the die holders;
beginner) the chaser will bite into
the surface and begin to form a spiral cut; as the other points on
the chaser engage with the spiral, the action becomes, to an
extent, self-stabilising and easier to perform; however, many
passes are normally required before the full depth of the thread
is generated.
How was the first thread generated? You can repeat the process
yourself. Take a wooden rolling pin and place it on a flat
surface. Pick up a knife, hold it horizontally and place the sharp
edge on the top surface of the roller near one end. Now twist
the blade a little horizontally, say 10º or so, press down and use
it to roll the pin away from you. As the pin rolls a spiral line is
 generated. Deepen the cut line into a V-shaped groove and you
have a thread. Unfortunately, unless you are the cook in house,
you now in dead trouble with SWMBO.
An interesting difference exists between "English" threads (a
definition that includes American types) and Metric. All
English (sometimes called "Imperial") and American threads
are based on what happens within the boundary of a single inch
length. Inside that inch length you might have any number of
turns (pitches) - though typically restricted to a range extending
from 4 to 56 t.p.i . Metric threads are arranged differently, there
is no fixed length into which the pitches must fit and each is
arranged to be a fraction, or multiple of, a millimetre. The
effect of this is illustrated if you take the centre of a valley
anywhere on a threaded rod (with a pitch in whole inches) and
measure one inch in either direction - the finish point will also
be in the centre of a valley. However, if the pitch is a fraction,
say 6.5 t.p.i., then you have to measure two inches, to
accommodate the effect of the fractional 1/2). Metric pitches
are designed so that the valleys centres are a fixed distance
apart in whole millimetres or fractions of a mm - for example:
0.25 mm, 0.75 mm, 1.0 mm, 1.5 mm, 2.5 mm, etc. If you
measure a metric thread as for an inch type - but using a fixed
unit of metric length (such as 100mm) - you will find that
whilst some pitches do end in a valley centre, most do not -
because they don't divide exactly into 100. Whilst for all
practical purposes this difference does not matter, it creates an
interesting effect when screwcutting for, whilst just a single
gear is needed on the thread-dial indicator on an English lathe,
on a metric machine two and sometimes three are fitted to
cover the range of common pitches. In fact, an impractical six
gears would be required to cover every metric-pitch
requirement.
The world's most common thread? It must be the 1/4" x 20 t.p.i.
Whitworth form found in the base of every camera that allows
it to be fitted to a tripod or other mount. It's common to all
camera maker and every model they produce - though some
heavier professional types have, as a concession, fitted with a
more robust 3/8" x 16 t.p.i.

The Lathe Countershaft

We can supply parts & accessories for machine tools of all kinds: cross-feed screws
and nuts, T-slotted cross slides, backplates, gears of kinds, parts repaired, etc. one-
off items a speciality. email your needs
Parts Home Page Screwcutting Backgear Watchmaker's
Lathe
Quick-change Toolholders Fitting a Chuck Spindle Nose
Fittings More Names of Parts

Most small electric motors in Britain spin at 1425 rpm, whilst those in
the USA and Europe are usually marked a little faster at 1600 to 1700
rpm or so.
If the lathe spindle was to be driven directly from one of these motors,
even using a small pulley on the motor shaft, and a larger one on the
lathe, it would be turning far too fast to be useful for the majority of
jobs. Hence, it is necessary to introduce some way of reducing the
speed - and that is the job of the countershaft. In a typical
arrangement, illustrated below, the motor is fastened to a vertical cast
iron plate, hinged at it base, and fitted with a small pulley on its
spindle. Because the 1500 rpm motor is driving a much larger pulley
above it in a ratio of something like 5 : 1 - the speed of the upper
pulley is reduced to 300 rpm (1500 divided by 5).
On the same shaft as the large pulley is a set of three pulleys, usually
identical to those on the lathe, but arranged in the "reverse" order. If
the middle pulley on the countershaft is made to drive the identically-
sized pulley on the lathe spindle that too, of course, will turn at 300
rpm. The pulleys each side of the centre are normally arranged to
halve and double the speeds - hence the creation of speed set covering
a useful 150 rpm, 300 rpm and 600 rpm.
It is a simple matter to fit both a small and a larger pulley on the
motor shaft, and two correspondingly larger pulleys on the
countershaft, and so double the number of available speeds - and then
to replace the three-step pulley with a four-step - so creating (with a
backgear) a sixteen speed drive that, typically, would give a range
starting at 25 and extending all the way up to a little over 2000 rpm.
One question that crops up frequently is, "I don't have a pulley on my
motor. How big should it be ?" The real answer depends upon many
factors but as a starting point for lathes up to 5-inches in centre height
with plain bearings aim for a top speed of around 800 rpm - and with
roller bearings 1200 rpm. It may well be that higher speeds can be
obtained safely, but it would be unwise to go beyond these levels as a
starting point. To get a feel for the calculations needed first measure
the diameter of the large pulley on the countershaft - say 10 inches. A
2-inch diameter pulley on the motor will give a reduction of 10
divided by 2 = 5 to 1. Divide the motor speed (say 1425 rpm) by 5
and the countershaft will be revolving at 285 rpm. If the lathe has a 3-
speed headstock pulley the next higher speed will be twice as fast
(570 rpm) and the one below half as fast (142 rpm). This set is
obviously a little slow so, increasing the motor pulley to 3-inches in
diameter would give speeds of 214, 428 and 856 rpm; that would be
a better solution for, combined with the average 6:1 reduction
backgear, it would produce a bottom speed of 36 rpm, an ideal rate
for the inexperienced to use for screwcutting. If your countershaft
pulley is a different diameter, simply substitute the appropriate
measurements into the "equation" and experiment with different
motor pulley sizes until you have as close a fit to the ideal as you
can..
Typical South Bend
countershaft unit as
used on the 9-inch
"Workshop" lathe.
This employed an
unusual but effective
trick: the motor pulley
was a V but the large
countershaft pulley
was flat.
A V belt was used for
the drive - this had
plenty of grip on the
small motor pulley
and, because it was so
well wrapped round
it, plenty on the flat
pulley as well.

The neat, built-on

16-speed
countershaft unit
of an Atlas lathe.
An earlier form of
Atlas countershaft
which produced a
"deep" speed range -
very slow to very fast
- without the use of
backgear.
Another form of very
compact countershaft
drive - contained
within the cabinet
stand of a Logan with
a V belt drive going
vertically upwards to
the lathe above.
Home Machine Tool Archive
Machine-tools for Sale
E-MAIL Tony@lathes.co.uk

The Lathe -
Headstock & Backgear
We can supply parts & accessories for
machine tools of all kinds: cross-feed screws
and nuts, T-slotted cross slides, backplates,
gears of kinds, parts repaired, etc. one-off
items a speciality. email your needs
Parts Home Page Screwcutting
Countershafts Watchmaker's
Lathe
Quick-change Toolholders
Fitting a Chuck Spindle Nose
Fittings More Names of Parts

BACKGEAR
As its name implies, "backgear" is a
gear mounted at the back of the
headstock (although in practice it is
often located in other positions) that
allows the chuck to rotate slowly
with greatly-increased turning
power. For a novice the ability to run
a workpiece slowly might seem
unnecessary, but a large-diameter
casting, fastened to the faceplate and
run at 200 r.p.m. (around the bottom
speed commonly found on a lathe
without backgear) would have a
linear speed at its outer edge beyond
the turning capacity of a small lathe.
By engaging backgear, and so
reducing r.p.m. but increasing
torque, even the largest faceplate-
mounted jobs can be turned
successfully.
Screwcutting also requires slow
speeds, typically between 25 and 50
r.p.m. - especially if the operator is a
beginner, or the job tricky. A bottom
speed in excess of those figures (as
found on most Far Eastern and some
European "Continental" machines)
means that screwcutting - especially
internally, into blind holes - is, in
effect, impossible. These lathes are
advertised as "screwcutting" but
what that really means is just power
sliding - a power feed along the bed.
With these machines even if you go
to the trouble of making up a
complex pulley system to reduce the
spindle speed (like the early Atlas 9-
inch) you will find the torque
required when turning large
diameters at slow speeds causes the
belts to slip. The only solution is a
gear-driven low speed - and so a
properly-engineered small lathe, with
a backgear fitted, not only becomes
capable of cutting threads but can
also tackle heavy-duty drilling, big-
hole boring and large-diameter
turning and facing; in other words, it
is possible to use it to the very limits
of its capacity and strength. To show
how important backgear has always
been considered examine the small
English-made metal turning lathes
made from the mid 19th century
onwards: nearly every one was so
equipped.
For a further explanation of the
desirable features required in a small
lathe, click HERE.
The backgear is a clever but
essentially simple mechanism
probably conceived by Richard
Roberts, an English engineer
and prolific inventor, around
1817.
In the picture above (a 1934
Atlas lathe) the 4-step V-pulley
(V) has a small gear (SG)
permanently attached to its
smaller end. The entire length
of V-pulley and gear are
bushed - and able to rotate
freely on the headstock spindle.
The large "Bull Wheel" (BW)
is keyed to the spindle (and
always rotates with it) and can
be connected to the V-pulley -
and disconnected from it - by a
pin (P) which is often spring-
loaded.
In normal use the V-pulley is
rotated by the drive belt and the
spindle made to turn through
the action of the pin driving the
Bull Wheel.
To use the backgear the lathe is
stopped, pin is withdrawn
(leaving the V-pulley and small
gear free to rotate) and the
Backgear (BG) rotated on its
eccentric shaft to bring it into
mesh with the other gears. On
starting the lathe the action is
now as follows: the pulley is
rotated by the drive belt, the
small gear (SG) on the V-
pulley (V) drives the larger of
the two backgears - which in
turn causes the small gear at the
other end of its shaft to rotate.
This smaller gear drives the
Bull Wheel (B) , and hence the
spindle, at a greatly reduced
speed (normally in the order of
6 : 1) but increased torque.
Examination of the headstock
pulley and the backgear shaft
may well reveal the presence of
oil holes; these are important
for, when working in backgear,
considerable forces are being
transmitted and the whole
assembly requires frequent
lubrication if it is to work
reliably. If the pulley is allowed
to seize on the headstock
spindle considerable time - and
possibly money - will have to
be spent in order to free it off.
Not all backgears engage like
the one above some, like the
one on the 1906 Drummond
illustrated below, slide into
position whilst others are held
in a forked bracket and slide
into position. Some are even
built into the larger end of the
headstock pulley and operate
on a "epicyclic" principal, not
unlike that of a Sturmey-Archer
hub gear on a bicycle.
There is often a small mark on
the pulley to show where the
pin through the bull wheel will
engage (if this is missing, one
could, with advantage, be
made). The face of the pulley is
often not a simple flat surface
but hollowed out with a small
drilled boss provided to carry
the pin; if just pushed in at
random and the lathe started the
pin will catch on the side of the
boss and bend.
If backgear constantly jumps
out of engagement there may
be an adjustable friction screw,
hidden away at the back of the
casting, that will solve the
problem.

On this wonderfully-original,
early Drummond lathe the Bull
Wheel and Drive Pulley are
connected together not with a pin,
but a substantial nut and bolt. The
"head" of the bolt engages with a
slot in the periphery of the pulley
wheel (not the notch cut in the
pulley to show the operator where
this is).
The backgear is slid sideways
into its operating position - and
held by a pin that passes through
the casting and engages with a
slot cut in the backgear shaft.

lathes.co.uk Home Page

Machine Tool Archive
Machine Tools For Sale &
Wanted
E-MAIL
tony@lathes.co.uk

The
Watchmaker's
Lathe
Names of Parts
and General Notes
We can supply parts & accessories
for machine tools of all kinds:
cross-feed screws and nuts, T-
slotted cross slides, backplates,
gears of kinds, parts repaired, etc.
one-off items a speciality. email
your needs
Parts Home Page
Screwcutting
Countershafts Backgear
Quick-change
Toolholders Fitting a
Chuck Spindle Nose
Fittings More Names of
Parts
An early Moseley Lathe
with parts (inadequately)
named by the maker.

1. Headstock Spindle
2. Throat pin 3.
Loose bearing 4.
Loose bearing pin
5. Adjusting nut
6. Front bushing 7.
Rear Bushing 8.
Front inside shield
9. Rear inside shield
10. Front outside shield
11. Rear outside shield
12. Pulley
13. Pulley Hub
14. Pulley screw 15.
Draw-in spindle
16. Draw-in spindle wheel
17. Frame
18. Index pin 19.
Bolt
20. Spring
21. Eccentric
22. Lever 23.
Pointed Centre
24. Spindle
25. Spindle Button
26. Spindle Binder 27.
Frame
28. Bolt
29. Spring
30. Eccentric 31.
Lever
32. Slide
33. Pivot Screw
34. Pivot Screw 35.
Post
36. Lever
37. T graver rest
38. Shoe 39.
Shoe bolt
40. Bolt pin
41. Bolt washer
42. Bolt spring 43.
Bolt nut
44. Bed
45. Base
46. Base bolt 47.
Bolt washer
48. Ball nut

Watchmakers'
Lathes
Although there are various
designs of watchmakers'
lathe, some dating back to
the late 1700s and
including specialised
models - for example
"fiddle" lathes, "steel
turns", Jacot, Swiss, Swiss
Universal (also called the
English Mandrel) Bottum
and Dracip - more modern
examples can generally be
divided into two types: the
lighter "Geneva" and
heavier "WW". The
"Geneva" can be
recognised by a round bed,
with a flat machined along
the back for its full length
and nearly always
supported on a single foot.
These lathes, invented in
1859 by Charles S.
Moseley in the U.S.A.,
generally take a 6mm or
8mm collet and were
designed only for lighter,
very high-precision work.
The "WW" (Webster-
Whitcombe), is the more
popular and versatile
machine and also of
American origin, from
around 1889. The centre
height of the WW was
usually 50 mm, though
very occasionally 65, 70
mm and other figures are
encountered. The bed was
of heavy construction,
formed with a 37 mm-wide
flat on the top and a 60-
degree bevel along each
edge, and carried a
headstock spindle to accept
8, 10mm or 12mm collets.
Larger than the WW type
are what might be called
"toolmakers' or "bench
precision" lathes: these
vary in size from the
Schaublin 65 and 70 (the
latter being the most
popular and frequently-
encountered machine in the
professional watchmaker's
workshop) to larger
examples such as the
Schaublin 102 and models
by makers such as Boley,
Lorch, Leinen, Stark,
American Watch Tool
Company, B.C. Ames,
Wade, Pratt & Whitney,
Rivett, Cataract, Hardinge,
Elgin, Hjorth, Potter,
Remington, Sloan & Chace
and others. Whilst useful
machines in a precision
workshop these are outside
the scope of this article.
There were dozens of
brands of watchmakers'
lathes and a lot of "badge
engineering" went on. This
was compounded by
accessories being
interchangeable between
makes so it is entirely
possible that a lathe has
been "made up" from
others. However, it's very
unlikely that the bed,
headstock and tailstock will
be from different
manufacturers; if they are,
be wary.
You can see other
examples of watch and
instrument makers' lathes
and their accessories here:
http://www.lathes.co.uk/pul
tra
http://www.lathes.co.uk/bol
ey/page3.html
http://www.lathes.co.uk/bol
ey/page4.html
http://www.lathes.co.uk/bol
ey/page5.html
http://www.lathes.co.uk/bol
ey/page6.html
http://www.lathes.co.uk/bol
ey/page7.html
http://www.lathes.co.uk/mo
seley
http://www.lathes.co.uk/ber
geon
http://www.lathes.co.uk/bt
m
http://www.lathes.co.uk/lev
in (USA)
http://www.lathes.co.uk/der
byshire (USA)
http://www.lathes.co.uk/fav
orite
http://www.lathes.co.uk/im
e
http://www.lathes.co.uk/lor
chschmidt
http://www.lathes.co.uk/lor
ch
http://www.lathes.co.uk/der
byshire
http://www.lathes.co.uk/bt
m
http://www.lathes.co.uk/im
e
http://www.lathes.co.uk/lei
nen
http://www.lathes.co.uk/rol
ls-royce
Availability
Watchmakers" or
Instrument-makers' lathes
can be very valuable,
especially if they are in
fine, original condition and
complete with lots of
accessories. Buying just a
basic lathe with bed,
headstock tailstock and T-
type tool rest can be false
economy - there are lots of
these about, at attractively
low prices, but the real
value is in the extras that
allow the lathe to be used
as a miniature "machining
centre" - as originally
intended - to cut, for
example, wheels (gears),
mill small parts and hold
tiny, awkwardly shaped
mechanisms for repair and
restoration. Because there
is considerable competition
for accessories, if your
basic lathe has to be
equipped one part at a time
much time, effort and
money will be expended -
hence, if you can, find a
fully-equipped lathe; this
will be a much better
investment and a lot easier
for you, or your heirs, to
sell.
If you are looking for one
of these machine I would
strong recommend
advertising for one. There
are thousands sitting
unused whose owners will
never get round to
advertising them - a
"wanted" advertisement
might just encourage them
to get in touch:
Accessories:
Typically, the most
valuable watchmakers' or
instrument-makers' lathe
would still be in its original
wooden box with a wide
range of equipment
including as many of the
following as possible:
Compound slide rest -
screw-feed or lever action
Collets - a set of around 20
"Wire" (often called "split
chucks"),
Collets - "Wheel" type in a
set of 5 or 6
Collets - "Ring Step" type
in a set of 5 or 6
Box Chuck
Chuck conventional 3-jaw
Self-centring (sometimes
called a "Universal
Chuck") in ring-scroll
(knurled ring round the
outside) and key-operated
models,
Chuck conventional 4-jaw
Independent
Cutting tools - as large a
collection as possible
The following "chucks"
mounted on collets:
Chucks - balance
Chucks - box type with
screws through the body to
hold jobs
Chucks - brass split type
(sometimes called jewel
type) to fit inside larger
steel collets
Chucks - button or crown
usually in sets of 10
Chucks - carrier for driving
work between centres
Chucks - circular-saw type
Chucks - emery wheel
Chucks - lantern in bronze
or steel,
Chucks - wax
Chucks - wood screw
Chucks - wood turning
Compound Slide Rest
Drill chuck for headstock
or tailstock use
Drilling plates - self-
centring
Drive Plate
Eye glass on adjustable
holder
Fixed steady
Jacot Drum
Lapping attachment
Pivoting attachment
Saw table
Sinking tools
"Mandrel" - this has the
appearance of a spare
headstock with a
"faceplate" attached and is
used for super-precision
work
Micrometer-adjustable
boring head
Milling and Grinding
Spindle,
Pivot polisher
Pivoting attachment
Roller rest in single or
double-wheel types
Rose cutters
Screwcutting Attachment
with a set of Changewheels
Sinking tools
T-rest - the basic device to
rest a tool against.
Available in standard and
tip-over types
Tailstock chucks - also
known as "drill stocks" and
available with flat heads, V
heads and chuck type
Turning arbors
Topping or "rounding up"
tool
Two types of Tailstock
(sliding spindle and a
lever-feed spindle),
Tip-over or simple sliding
T-shaped Hand-rest,
Universal Faceplate and
Pump Centre,
Vertical milling Slide,
Wheel-cutting attachment
with division plate (to cut
what the laymen would call
gears but which are known
to the watchmaker as
"wheels").
Drive systems
Even when fully equipped
it is not unusual to find that
a watchmaker's lathe has
no drive system or even
motor. However, this is
rarely a problem for the
easiest and cheapest
solution is to use either the
motor from a sewing
machine or, preferably, a
proper "Parvalux" unit - the
latter available in 1-phase,
3-phase and DC types with
speed ranges spanning 0.2
to 10,000 r.p.m. The motor
can be bolted in place
behind the headstock and
driven by a special Swiss-
made round plastic belt that
can be flipped easily from
pulley groove to pulley
grove, there being no need
to make up the type of
hinged countershaft that a
larger lathe would need.
The writer can supply
Parvalux motors their
controller and the special
belting
Handbooks
Unfortunately no maker of
a watch lathes has ever
offered a proper handbook
for their products but,
happily, there is an
excellent hard-back book
available that does the
same job: "The
Watchmakers' Lathe". This
is a long-established
publication and, because
most of these lathes were
built along the same lines,
and use almost identical
accessories, the book is
able to give precise
instructions that apply to
all types.
UK post-paid delivery:
£18.75 EU post-paid
delivery: £19.75 World-
wide air-mail delivery: £26
(about US$67) email to
order

Manufacturers and
Brands
Genuinely high-quality
Watchmakers' lathes were
manufactured and branded
by, amongst others:
Accro
Adams George
American Watch Company
(C. S. Moseley-designed
lathe circa 1859)
American Watch Company
(A. Webster-designed lathe
circa 1859/60)
American Watch Tool
Company (Webster-
Whiitcomb improved-
design lathe of 1889 - the
WW model)
Ames
ARS
Bergeon
Boley
Boley-Leinen
Boston Watch Company
(C. S. Moseley-designed
lathe circa 1858)
Bottum
Boydon
B.T.M.
Cataract (Hardinge)
C.L.H.
Coronet
Derbyshire
Dracup
E.H.J. (E. H. Jones
machinery dealers and
commissioners)
E.M.E.
Favorite
Gamma
Gem (Gem Glorious)
Gentil (Star Lathes,
Switzerland)
George Adams (re-branded
Boley and Lorch, etc. and
cheaper imitations under
his own label)
Hardinge (Cataract)
Hammel, Riglander & Co.
Hopkins
IME
Jones (J & T Jones UK)
Lampert (U.S.A.)
Lanco (Lane Cove)
Leinen
Levin
Lorch (Lorch Schmidt)
Manhora
Mansfield
Marshall
Moseley
Nordan
Ohio
Paulson
Peerless
Perton
Precista
Pultra
Reliance
Rivett
Schaublin
Schmidt
Scomea (Société
Commerciale d'Outillage et
de Mécanique d'Aviation)
Simplex
Sloan & Chace
Star (R. Gentil & Co.
Company of La Brevine in
Switzerland)
Stark
Steiner
Swan
Taylor
T.C.M.
Waltham
Webster
Webster-Whitcombe (WW)
Whitcombe
Wiskum
Wolf, Jahn
Some of these are featured
in the Machine Tool
Archive

Early Drive Systems - Line Shafting

Until the 1930s, and in some cases for very much longer, most machine
shops had what would today be grandly called an "Integrated Power
System". At the heart of the system was a lovingly-cared-for engine,
steam or electric, that drove, via a convoluted belt and rope system, a
labyrinthine maze of pulleys hanging from bearings attached to girder
work inside the roof of the factory; that part of the drive system held in
the ceiling was referred to as "line shafting".
Each machine was attached to the shafting by a wide, flat belt, usually
between 1 and 6 inches wide with some sort of ancillary-control system
that involved the use of "fast-and-loose" pulleys. The latter was a simple
but ingenious system that involved the driven belt running first over a
"loose" or free pulley and, from that position, being able to be flicked
across to a "fast" pulley clamped to the shaft. Finally, another belt and
pulley set took the drive down to a machine on the floor below. Methods
of moving the belt were numerous and ingenious from a length of broom
handle to sophisticated and expensive controls involving foot pedals,
wires, links, bell-cranks and toggles.
Once an overhead drive system had been (expensively) installed in a
specially-prepared building, the nightmare of maintaining and constantly
overhauling the multitude of bearings and hangers, inconveniently and
dangerously located ten or twenty feet in the air, could begin. No wonder
Works Engineers clocked-off dreaming of a better solution; their
salvation eventually came in the form of the small, high-speed electric
motor that was able to provide each machine with its own, independent
power source. The tricky installation of a drive system could now be
delegated to the machine maker and, besides all the other advantages, if
you fell out with your landlord it was possible to pull out of your
Victorian dungeon and move across the road, or town, to somewhere
both more convivial and cheaper. It also meant that, with an appropriate
electricity supply, you could arrange your machines to optimise the
production requirements of any particular job and quickly rearrange
them again when it became necessary. Meanwhile, George, down the
road, stuck in his old-fashioned premises, still had to employ labourers
with wheelbarrows to shift 200 lb lumps of cast iron from one end of the
factory to the other as a job zigzagged haphazardly around the various
machine tools.
Another factor, and now a long-forgotten problem, was the question of
light; because there was no electricity to illuminate their interiors
Victorian factories had huge numbers of tall windows, glass inserts in
the roof and, for preference, were always sited and aligned to make the
most of available daylight. The original heavy and cumbersome
wrought-iron overhead line shafting and belts did an excellent job of
blocking light and even the advent of stronger, lighter and thinner steel
components in the mid 1800s did not significantly improve matters -
thus the advent of individually-powered machines meant that (just as the
light bulb came into use and night shifts started) factories became much
lighter, safer and more efficient places in which to work.

Home Machine Tool

Archive Machine-tools
for Sale
E-MAIL
Tony@lathes.co.uk

Dickson
Quick-change
Toolholders
Dickson Quick-set Tool
Holder
Screwcutting
Countershafts
Backgear The
Watchmaker's Lathe
Fitting a Chuck Spindle
Nose Fittings More
Names of Parts
We can supply parts &
accessories for machine tools of
all kinds: cross-feed screws and
nuts, T-slotted cross slides,
backplates, gears of kinds, parts
repaired, etc. one-off items a
speciality. email your needs

Although many designs of

quick-set tool holder have
been produced probably
the best known and most
widely used is that first
manufactured by
"Dickson" in the UK
using high quality steel,
hardened and ground,
finished to very close
tolerances and produced in
a variety of sizes to suit
lathes from 89 mm (3.5-
inch) to above 381 mm
(15-inch) centre height.
Ordinary and extra-long
toolholders to take
standard, parting, boring
and Morse taper bits are
available and, once
mounted in place on the
central block, can be
quickly adjusted in height
until the best cutting effect
is found and the setting
locked. This completely
obviates the need to fiddle
with packing pieces and, if
kept together, the holder
and tool can now be
guaranteed to drop back
into exactly the same
position every time they
are used. It is strongly
recommended that, in
order to get the best from
the assembly, a selection
of extra holders is
acquired so that each
commonly-used tool can
be given its own and left
in place.
Whilst the larger sizes are
largely immune to heavy
handling the three smaller
models should be treated
with care: it is not
necessary to brutally yank
up the adjustment and
retaining screws; instead,
just firm hand pressure
will lock the units
securely against the
heaviest work. Full details
of the Models and their
measurements can be
found below.
Spares for these units are
available.
These toolposts have been
widely copied in India and
China - using inferior
materials and indifferent
standard of fit. You might
be lucky and find a perfect
example but amongst
other faults reported are
clamping pins that snap
off, bases that are not flat,
V-grooves out of parallel
and toolholders that fail to
contact fully with the
 guides and wobble about.

The Lathe
Fitting a Chuck and
Making a Backplate
We can supply parts & accessories for
machine tools of all kinds: cross-feed
screws and nuts, T-slotted cross slides,
backplates, gears of kinds, parts repaired,
etc. one-off items a speciality. email your
needs
Screwcutting Countershafts
Backgear The Watchmaker's
Lathe
Quick-change Toolholders
Fitting a Chuck Spindle Nose
Fittings More Names of Parts
We can supply: replacement
chuck jaws
New plain and threaded
backplates and chucks - email
for details.
Some lathes ( especially larger
ones) often have chucks with
integral threads or other mounting
mechanisms - Long-nose Taper,
Camlock, ISO, etc. - but most
small lathes (and older larger ones)
use a simple "backplate" where a
suitably threaded disc - preferably
made from drawn cast iron - is
screwed on (or otherwise attached)
to the spindle nose and then turned
very carefully so that a spigot,
raised in its centre, will fit closely
into a recess in the back of the
chuck. At all costs avoid steel
backplates; they can bruise or
otherwise damage the spindle nose
and, if they become stuck, will be
much more difficult to remove.
Contrary to popular belief, the
bolts that pass through the
backplate and screw into the body
of the chuck do not provide a
location - they simply clamp the
two components together; the
alignment of the chuck on the
backplate (and hence its position
relative to the centre line of the
headstock spindle) depends upon
the spigot, (machined on the
backplate), being made a very
close fit within the chuck body.
A further important consideration
concerns the surfaces of the
backplate and chuck that come into
hard contact with each other. This
is determined (of course) by which
surfaces the mounting bolts pass
through - and can be either on the
raised outer ring (annulus) of the
chuck, or the circle formed inside
it. Whichever surfaces come into
contact make sure that the other
two (non-contact surfaces) have a
little clearance between them -
about 0.025" (0.5 mm) is sufficient
- in other words, the depth of the
spigot must not be too deep, nor
too shallow.
Needless to say, if you have more
than one chuck each will require
fitting to its own backplate. Even
when chucks have identical backs
removing and refitting them (on a
shared backplate) would not only
waste time but introduce
inaccuracies.
 Mounting a New Chuck

1. Make sure that the threads of the

(cast-iron) backplate and spindle
are thoroughly cleaned and very
lightly oiled. Screw the backplate
on firmly, using hand pressure
only.

3. Before machining starts find a

suitable bar, mount it between
centres and allow the tailstock to
apply a little pressure towards the
headstock. Doing this will
eliminate any spindle end-play (if
it exists) - a vital requirement when
making very accurate facing cuts.

3. Use a pair of inside calipers to

measure the diameter of the recess
in the back of the chuck; transfer
this measurement to a pair of
outside calipers and machine a
spigot that is oversize by about
1/64" (0.5 mm); if you doubt your
skill to do this, simply leave the
spigot a little larger.
The face of the backplate that the
chuck pulls up against must be
dead flat; once the oversize spigot
has been formed spend several
minutes raising just "dust" across
this surface to make sure that it is
as flat and as smooth as possible.
You might want to test this by
running a dial-test indicator over it;
ideally, the run-out should not
exceed 0.0002" (0.005 mm).

4. At the junction of the "flange

face" and the "vertical wall" of the
spigot (Fig. 2), a small undercut
should be made. This will allow
the finishing cuts on the wall to be
taken right down so that there is no
interference between the "corners"
on the backplate and those on the
chuck..

5. Before the last cuts are taken,

the turning tool should be changed
for one shaped so that it will cut
down the wall of the spigot - the
tool being moved backwards and
forwards along the lathe bed not
across.
It's very easy to get the size of the
spigot approximately right, but the
final cuts, when its diameter is
approaching the size that will allow
it to be pressed firmly into the back
of the chuck, must be taken very
carefully indeed - only "dust"
should be raised from the surface
by the cutting tool.
The chuck should be tried for fit
after each pass of the tool - and
remember, the one deeper cut
made to save time will be the one
that ruins the job. As the tool
reaches the bottom of the spigot
wall allow it to enter the
previously-formed undercut
section.
As an alternative to using the
whole carriage to move the cutting
tool some experienced fitters
suggest using the top slide only;
this is done by locking the carriage
to the bed and ensuring that, when
the top slide is set on its zero mark,
it cuts parallel - a test cut on some
other material to verify this will be
time well spent.

6. Leave the chuck on a hot

radiator for an hour to expand it
slightly before starting the
machining operation; if you decide
to do this, remember to pick it up
whilst wearing an insulated glove -
and don't overdo the heating,
otherwise you will have a difficult-
to-remove "shrink" fit rather than
one that can be assembled with a
firm push or a very light tap with a
hide-faced mallet.
If time is short put the chuck into a
strong plastic bag and lower it into
a bucket of hot water for 10
minutes.

7. When the backplate is the

correct size, mark out and drill the
bolt holes. This is easily done if
engineers' blue, or a smear of red-
oxide paint (or even chalk) is put
on the backplate before fitting it to
the chuck; when the plate is
removed the location of the bolt
holes will be apparent. Carefully
mark out and drill the holes so that,
as the bolts pass through the
backplate, there is no possibility of
them touching the sides and
straining the backplate out of line;
make them at least 1/16" (1.5 mm)
oversize on diameter.
As final check make sure that the
mounting bolts do not bottom out
in their tapped holes and that chuck
and backplate are drawn solidly
together.

8. If the backplate is a larger than

the chuck, finish turn it to the
chuck-body diameter and, for
safety, radius the rear edge; when
this is done, scribe a fine line
across the chuck body and
backplate so that, when the chuck
is removed for dismantling and
cleaning, it can be replaced in the
same relative position.

9. If your 3-jaw chuck has two or

more key holes, one of them may
have a circle, or other mark,
stamped alongside it to show that it
should used for final tightening. As
a chuck wears it is not unknown
for one of the other key holes to
provide a more accurate grip.

10. If you check the accuracy of

your new chuck, make sure that
you use a piece of precision ground
bar and mount the magnetic base
(or other device) holding the dial-
test indicator onto the lathe bed,
not the saddle or compound slide
rest. Chuck makers cover their
backs by quoting pessimistic
figures for alignment - typically
0.005" two inches away from the
jaws; in practice, a good chuck can
be within 0.001" at this distance, or
even better - but you will not find
anyone willing to guarantee it.

11. When using the chuck

remember its intended purpose - a
precision work-holding device: it is
not a Record No. 6 all-steel bench
vice. The most common fault
found on 3-jaw chucks (apart from
wear) is one or more broken jaw
threads caused by over-tightening
when opened out to maximum
capacity.

12. If you can afford it, have two

3-jaw chucks in operation; one for
"rough" work, to take the stress
and strains of heavy use, the other
employed only for the finest
finishing of materials already part-
machined. By doing this you will
always have one chuck that
remains an accurate, easily-used
and reliable work holder.

Making a Backplate for a

Screwed Spindle Thread

Unfortunately there are several

factors that combine to make this a
rather more difficult task than it at
first appears. Because the diameter
and pitch of a spindle-nose thread
is often not to a "standard" (and
combined with wear in use),
machining a thread inside a
backplate to match it can be tricky
- unless the spindle is removed
from the lathe and is used to check
the job as it progresses. You can't
remove the job from the lathe and
try it on the spindle - once
removed, it can never be replaced
with sufficient accuracy for a cut to
start where it left off.
Of course, if spindle thread is a
Whitworth or metric standard you
may be able to locate a tap of the
appropriate size and find that a
thread cut with is perfectly
satisfactory; however, large-
diameter taps are hard to find, and
expensive.
There is one well-known technique
that will enable an accurate
measurement of the thread
diameter to be made and the
problem of making a backplate
with accurate threads solved.
The "3-wire method"
This makes use of freely-available
brazing rods. A diameter of rod
needs to be chosen so that, once in
position it protrudes just above
thread crests. The illustration
below should make it clear as to
the shape to be used - this cleverly
allowing the wire to stay in place
whilst readings are being taken.
Using a micrometer measure the
diameter over the wires at 6 points
along the length of the thread and
average the result.
If a sketch is now produced
showing:

the length of the thread -

the length and diameter of

any plain "register"
inboard of the thread -

the number of pitches per

inch (or mm pitch) -

the thread angle (usually

55 or 60 degree) -

the average diameter over

the two "3-wires" -
a skilled turner should - having
possession of the wire - be able to
reproduce the thread accurately.
Of course, as mentioned earlier, if
the spindle can be removed from
the lathe and tried into the
backplate as work progresses, the
whole process is made so much
easier.
A note on the "register" of the
spindle end might also appropriate
- the register being that small
length of plain shaft between the
thread and the abutment face.
Although by its name one might
assume this to be a critical part of
the assembly it is not, and has no
bearing on the accuracy of the
backplate-to-spindle fitting.
Tony Griffiths
3-wire method of
duplicating
thread
dimensions

Lathe Spindle Nose &

Backplate Fittings
We can supply parts & accessories for
machine tools of all kinds: cross-feed
screws and nuts, T-slotted cross slides,
backplates, gears of kinds, parts
repaired, etc. one-off items a speciality.
email your needs
Backplates and chucks can be
supplied in most of these
fittings
Screwcutting Countershafts
Backgear The Watchmaker's Lathe
Quick-change Toolholders Fitting a
Chuck Spindle Nose Fittings More
Names of Parts
The well-known "cam-lock"
spindle fitting
For many years chucks,
faceplates and catchplates
were simply screwed onto
the end of the lathe's
spindle; a bewildering
variety of types and sizes
of thread were used and
non were standardised
between manufactures.
Although cheap to
manufacture and perfectly
adequate for most
purposes, especially
amateur use, threads do
have serious limitations
centred around safety,
rigidity and ease of
removal and replacement.
To take just one example:
a threaded fitting cannot
safely be run backwards
and, whilst a chuck might
happily stay in place as a
lathe accelerates up to top
speed in reverse, once
there it cannot be so easily
stopped. Legion are the
number of serious
accidents caused where an
operator has stated a lathe
in reverse, realised his
mistake, and then (without
thinking) applied the
spindle brake. Once the
chuck starts to unscrew
the workman can do
nothing but watch in
horror as the 200 lb mass,
rotating at 800 rpm,
accelerates down the
length of the workshop
smashing machines and
people unfortunate enough
to get in its way.
To overcome this, and
other limitations of
threaded fittings, many
alternative designs have
appeared over the years
that are safer, more rigid
and both easily mounted
and removed.: the
following pages illustrate
the most popular and
frequently encountered
types for both direct and
backplate mounting. To
understand the fitting look
through the links to both
Spindle Nose Fittings and
Backplate Fittings.

SPINDLE NOSE
FITTINGS
American long Taper
with Drive Key and
Draw-nut Types L00,
L0, L1, L2 and L3
AMERICAN
STANDARD SPINDLE
NOSES - Direct
Mounting
American short Taper
with Bolt or Stud Fixing
Types A1, A2, B1 and
B2
American short Taper
with Camlock Fitting
Type D1
British and ISO
Standard Spindle Noses
- Direct Mounting
British & ISO Short
Taper with Bolt or Stud
Fixing
British & ISO Short
Taper with Camlock
Fixing
British & ISO short
Taper with Bayonet
Ring Fixing
German Standard
Spindle Noses

BACKPLATE
FITTINGS
Cam-lock D1-2", D1-4"
etc
American Long Taper L
Types L00, L1, L2 and
L3
Short Taper A-1, A-2, B-
1, B-2, with Bayonet
"A Type" Screw Fitting

Home Machine Tool

Archive Machine-tools
for Sale
 E-MAIL
Tony@lathes.co.uk

The Lathe
We can supply parts &
accessories for machine tools of
all kinds: cross-feed screws and
nuts, T-slotted cross slides,
backplates, gears of kinds, parts
repaired, etc. one-off items a
speciality. email your needs
Names of Parts -
Maker's Examples
Parts Home Page
Screwcutting
Countershafts
Backgear
Quick-change
Toolholders
Watchmaker's Lathe
Spindle Nose Fittings
Fitting a Chuck

An early Myford
ML2 - labelled
by the makers.
South Bend's rather
basic labelled
photograph.
The lathe according to
Clausing.

Home Machine
Tool Archive
Lathes for Sale
E-MAIL
Tony@lathes.co.uk

The Lathe
Names of Parts
- Maker's
Examples
Parts Home Page
Screwcutting
Countershafts
 Backgear
Watchmaker's
Lathe Fitting a
Chuck More
Names of Parts