Making a Screw Thread

Elementary Knowledge of Screws

Machine screws are extensively used for securing parts. The number of different types and sizes of
machine screws, nuts bolts prohibit the possibility of introducing them all here so the following
information addressed the elementary information only.
Types of Threads
!lmost of the thread have triangle shaped threads. "n the other hand, s#uare shaped and trapezoid
shaped thereads are used moving machinery which need high accuracy, such as a lathe.
$n respect to thread standards, there are a metric thread %M&, a parallel thread for piping %'(&, a
taper thread for piping %'T&, and an unified thread %)*+, )*(&. The following information is
related metric threads, because they are the most widely used in ,apan and many countries around
the world.
Terms used for Threads
(igure - shown an image of a thread. "ne of
the most important terms used is that of the
outer diameter. $n the case of a metric thread,
the bolt is named in accordance with its outer
diameter e.g a bolt with a . mm outer
diameter is /nown as an M. bolt.
The 0'itch0 of the tread is another important
feature of a thread. The pitch is defined as
the interval %distance& between ad1oining
threads. e.g. *uts bolts must have the
same pitch as well as diameter if they are
going to be used together.
The principles of cutting threads in nuts and
bolts is that the bolt %male thread& is usually
cut from a rod of material which has the
same diameter has the intended finished bolt.
The nut is made from a larger stoc/ witch
has a hole drilled through it that is slightly
larger than that of the rod diameter. ! thread
(ig.-, Terms of Screw
of the same pitch is then cut which results in
two mating threads. The same principles
apply for cutting holes in places and other
wor/ pieces. %such an in the cylinder
discussed earlier.&
(ig.2, $magine of Thread +utting 'rocessing
Screw and +learance 3ole
Screws are typically used for securing
mating parts. 4hen two pieces are 1oined
together using screws, one piece is made
with threads, and another piece is made with
clearance holes, which have bigger diameters
than that of the screws. $f the diameter of the
clearance hole is too small, the piece cannot
be assembled as the screw will not fit
through the hole. !lso, if the diameter of the
clearance hole is too big, , the piece will be
loose as the hole will provide a sloppy fit.
Therefore, we must provide ma/e suitable
diameter clearace holes. !s a 0rule of
thumb0, the diameter of the clearance hole
has more -5 6 than the diameter of the
screw. (or examples, the clearance hole for a
M7 screw has 7.2 mm or 7.. mm diameter.
the clearance hole for a M8 screw has 8.2
mm or 8.. of diameter. !nd we would ma/e
a hole with ... mm of diameter for a M.
screw.
(ig.7, Screw and +learance 3ole
Thread Ma/ing 'rocess
4hen we ma/e the male thread, generally
we use a die tool. 4hen we ma/e the female
thread, we use a tap tool. $f we do not have
the suitable tools, we can also ma/e the
thread using a lathe as described in +hapter
7.
+aution
4hen we ma/e the threads using the tap
or the die, care should be ta/en in respect
for the following.
%-& Start the thread with a perpendicular
positioning of the tap or the die.
%2& Turn the tap or die in #uarter turns and
0bac/ off0 #uarter turns to remove melat
chips so that they don9t clog the tool.
%7& !lways use a cutting oil.
(ig.8, Tap and :ie
Tread +utting using a 3and Tap
(igure . shows taps which are used to ma/e
female threads. They are usually used with a
tap handle as shown in (igure ;. $n respect
to the tread cutting process, we first, we
ma/e a hole with suitable diameter and
suitable depth %see Table -&. *ext, we start to
turn the tap in a cloc/wise direction.
There are typically three types of taps used
as seen in figure .. "f the three tap types
there is a tapered tap to facilitate the initial
thread cutting, an intermediate type that is
used to progress the thread after it has been
started and then finally, a 0<ottoming0
thread which is used to obtain the full thread
depth when cutting a thread that does not go
the whole of the way trough the piece.
Taps can be easily bro/en and if the tap is
(ig.., Taps
bro/en in the wor/ piece, it can be almost
impossible to remove. $t is therefore, very
prudent to ta/e care to ensure that metal
chips do not build=up in the tap and also that
the tap does not overheat as a result of the
cutting process through the use of a cutting
lubricant.
>ecommended Tap 3ole
Size
Table - lists diameters of
hole sizes for metric female
threads and piping threads
%'T, '(&. 'lease note that
the diameter of the hole
e#uals the approximate
difference of the diameter of
the thread and the thread
pitch. $t may be necessary
the allow a grater hole
clearance if for example we
were ma/ing a thread in
hard stainless steel.
Table -, >ecommended Tap 3ole Size
+utting using a 3and :ie
(igure ? shows a die and a die handle which are
used to ma/e male threads. The procedure of the
threading is the same of the taps. <ut it is more
difficult to start the thread cutting process than
with tapping as dies do not have an e#uivalent to
a tapered starting tap with perpendicular than the
tapping.
The thread cutting process using a die usually
typically results in a smaller diameter of the
original piece so care needs to be ta/en in
selecting the correct size stoc/. $f the stoc/ is too
small, this will result in a shallow thread depth
resulting in an unsatisfactory thread. The die also
created a bevel on the thread which is necessary
for a close fit.
$f you have a lathe, the 1ob of cutting a thread
can be easier as it is possible to use the
0ST"''E:0 lathe to assist in starting the thread
as shown in figure @. The die is pushed by the
drill chuc/ aligned perpendicularly to the piece
and after. !fter enough thread is cut, the drill
chuc/ is removed and the die handle is then
turned by hand.
(ig.?, !
:ie and !
:ie
3andle
(ig.@, Thread Ma/ing using :ie
More on Threads
3ow does the screw ma/e perpendicularlyA
$f the thread needs to be held perpendicular
to the piece, then it is important that the
thread incorporate a shoulder to act as a
0load bearing surface0 as depicted in figure
-5.The threaded section does not have the
mechanical properties necessary to remain
perpendicular without such a shoulder.
(ig.-5, 3ow to Ma/e 'erpendicular Screw
Screw thread
(rom 4i/ipedia, the free encyclopedia
Internal and external threads
illustrated using a common nut and bolt. The screw and nut pair can be used to convert tor#ue into
linear force. !s the screw %or bolt& is rotated, the screw moves along its axis through the fixed nut,
or the non=rotating nut moves along the lead=screw.
Screw
thread, used
to convert
tor#ue into
the linear
force in the
flood
gate. The
operator
rotates the
two vertical
bevel gears
that have threaded holes, thereby raising or lowering the two long vertical threaded shafts which
are not free to rotate %via bevel gear&.
! screw thread, often shortened to thread, is a helical structure used to convert
between rotational and linear movement or force. ! screw thread is a ridge wrapped
around a cylinder or cone in the form of a helix, with the former being called a
straight thread and the latter called a tapered thread. ! screw thread is the essential
feature of the screw as a simple machine and also as a fastener. More screw threads
are produced each year than any other machine element.B-C
The mechanical advantage of a screw thread depends on its lead, which is the linear
distance the screw travels in one revolution.B2C $n most applications, the lead of a
screw thread is chosen so that friction is sufficient to prevent linear motion being
converted to rotary, that is so the screw does not slip even when linear force is applied
so long as no external rotational force is present. This characteristic is essential to the
vast ma1ority of its uses. The tightening of a fastener9s screw thread is comparable to
driving a wedge into a gap until it stic/s fast through friction and slight plastic
deformation.
Contents
- !pplications
2 :esign
o 2.- Dender
o 2.2 3andedness
o 2.7 (orm
o 2.8 !ngle
o 2.. Eead, pitch, and starts
2...- +oarse versus fine
o 2.; :iameters
2.;.- Ma1or diameter
2.;.2 Minor diameter
2.;.7 'itch diameter
o 2.F +lasses of fit
o 2.? Standardization and interchangeability
o 2.@ Thread depth
o 2.-5 Taper
7 Standardization
o 7.- $S" standard threads
o 7.2 "ther current standards
o 7.7 3istory of standardization
8 Engineering drawing
. Deneration
; $nspection
F See also
? *otes
@ >eferences
-5 External lin/s
Applications
Screw threads have several applicationsG
(astening
o (asteners such as wood screws, machine screws, nuts and bolts.
o +onnecting threaded pipes and hoses to each other and to caps and fixtures.
Dear reduction via worm drives
Moving ob1ects linearly by converting rotary motion to linear motion, as in the leadscrew
of a 1ac/.
Measuring by correlating linear motion to rotary motion %and simultaneously amplifying
it&, as in a micrometer.
<oth moving ob1ects linearly and simultaneously measuring the movement, combining
the two aforementioned functions, as in a leadscrew of a lathe.
$n all of these applications, the screw thread has two main functionsG
$t converts rotary motion into linear motion.
$t prevents linear motion without the corresponding rotation.
Design
Gender
Main articleG Gender of connectors and fasteners
Every matched pair of threads, external and internal, can be described as male and
female. (or example, a screw has male threads, while its matching hole %whether in
nut or substrate& has female threads. This property is called gender.
Handedness
>ight= and left=
handed screw threads
The right=hand rule of
screw threads.
The helix of a
thread can twist in
two possible
directions, which is
/nown as
handedness. Most
threads are oriented so that the threaded item, when seen from a point of view on the
axis through the center of the helix, moves away from the viewer when it is turned in
a cloc/wise direction, and moves towards the viewer when it is turned
countercloc/wise. This is /nown as a right-handed %RH& thread, because it follows the
right hand grip rule. Threads oriented in the opposite direction are /nown as left-
handed %LH&.
<y common convention, right=handedness is the default handedness for screw threads.
Therefore, most threaded parts and fasteners have right=handed threads. Eeft=handed
thread applications includeG
4here the rotation of a shaft would cause a conventional right=handed nut to loosen
rather than to tighten due to fretting induced precession. Examples includeG
o The left hand pedal on a bicycle.B7C
o The left=hand grinding wheel on a bench grinder.
o The lug nuts on the left side of some automobiles.
o The securing nut on some circular saw blades = the large tor#ue at startup should
tend to tighten the nut.
$n combination with right=handed threads in turnbuc/les and clamping studs.B8C
$n some gas supply connections to prevent dangerous misconnections, for example in gas
welding the flammable gas supply uses left=handed threads.
$n a situation where neither threaded pipe end can be rotated to tightenHloosen the 1oint,
e.g. in traditional heating pipes running through multiple rooms in a building. $n such a
case, the coupling will have one right=handed and one left=handed thread
$n some instances, for example early ballpoint pens, to provide a 0secret0 method of
disassembly.
$n mechanisms to give a more intuitive action asG
o The leadscrew of the cross slide of a lathe to cause the cross slide to move away
from the operator when the leadscrew is turned cloc/wise.
o The depth of cut screw of a IStanleyJ type metal plane %tool& for the blade to
move in the direction of a regulating right hand finger.
Some Edison base lamps and fittings %such as formerly on the *ew Kor/ +ity Subway&
have a left=hand thread to deter theft, since they cannot be used in other light fixtures.
The term chirality comes from the Dree/ word for 0hand0 and concerns handedness in
many other contexts.
Form
The cross=sectional shape of a thread is often called its form or threadform %also
spelled thread form&. $t may be s#uare, triangular, trapezoidal, or other shapes. The
terms form and threadform sometimes refer to all design aspects ta/en together
%cross=sectional shape, pitch, and diameters&.
Most triangular threadforms are based on an isosceles triangle. These are usually
called V-threads or vee-threads because of the shape of the letter L. (or ;5M L=
threads, the isosceles triangle is, more specifically, e#uilateral. (or buttress threads,
the triangle is scalene.
The theoretical triangle is usually truncated to varying degrees %that is, the tip of the
triangle is cut short&. ! L=thread in which there is no truncation %or a minuscule
amount considered negligible& is called a sharp V-thread. Truncation occurs %and is
codified in standards& for practical reasonsG
The thread=cutting or thread=forming tool cannot practically have a perfectly sharp pointN
at some level of magnification, the point is truncated, even if the truncation is very small.
Too=small truncation is undesirable anyway, becauseG
o The cutting or forming tool9s edge will brea/ too easilyN
o The part or fastener9s thread crests will have burrs upon cutting, and will be too
susceptible to additional future burring resulting from dents %nic/s&N
o The roots and crests of mating male and female threads need clearance to ensure
that the sloped sides of the L meet properly despite %a& error in pitch diameter
and %b& dirt and nic/=induced burrs.
o The point of the threadform adds little strength to the thread.
<all screws, whose male=female pairs involve bearing balls in between, show that
other variations of form are possible. >oller screws use conventional thread forms but
introduce an interesting twist on the theme.
Angle
Main articleG Thread angle
The angle characteristic of the cross=sectional shape is often called the thread angle.
(or most L=threads, this is standardized as ;5 degrees, but any angle can be used.
Lead pitch and starts
0Threads per inch0 redirects here. (or woven fabrics, see !nits of textile meas"rement
# Thread co"nt.
Main articleG Lead $engineering%
Eead and pitch for
two screw threadsN
one with one start
and one with two
starts
(or other uses, see
&itch.
Lead HlidH and pitch are closely related concepts.They can be confused because they
are the same for most screws. Lead is the distance along the screw9s axis that is
covered by one complete rotation of the screw %7;5M&. Pitch is the distance from the
crest of one thread to the next. <ecause the vast ma1ority of screw threadforms are
single-start threadforms, their lead and pitch are the same. Single=start means that
there is only one 0ridge0 wrapped around the cylinder of the screw9s body. Each time
that the screw9s body rotates one turn %7;5M&, it has advanced axially by the width of
one ridge. 0:ouble=start0 means that there are two 0ridges0 wrapped around the
cylinder of the screw9s body.B.C Each time that the screw9s body rotates one turn
%7;5M&, it has advanced axially by the width of two ridges. !nother way to express this
is that lead and pitch are parametrically related, and the parameter that relates them,
the number of starts, very often has a value of -, in which case their relationship
becomes e#uality. $n general, lead is e#ual to S times pitch, in which S is the number
of starts.
4hereas metric threads are usually defined by their pitch, that is, how much distance
per thread, inch=based standards usually use the reverse logic, that is, how many
threads occur per a given distance. Thus inch=based threads are defined in terms of
threads per inch %T'$&. 'itch and T'$ describe the same underlying physical property
Omerely in different terms. 4hen the inch is used as the unit of measurement for
pitch, T'$ is the reciprocal of pitch and vice versa. (or example, a
-
P
8
=25 thread has 25
T'$, which means that its pitch is
-
P
25
inch %5.5.5 in or -.2F mm&.
!s the distance from the crest of one thread to the next, pitch can be compared to the
wavelength of a wave. !nother wave analogy is that pitch and T'$ are inverses of
each other in a similar way that period and fre#uency are inverses of each other.
Coarse vers"s fine
+oarse threads are those with larger pitch %fewer threads per axial distance&, and fine
threads are those with smaller pitch %more threads per axial distance&. +oarse threads
have a larger threadform relative to screw diameter, whereas fine threads have a
smaller threadform relative to screw diameter. This distinction is analogous to that
between coarse teeth and fine teeth on a saw or file, or between coarse grit and fine
grit on sandpaper.
The common L=thread standards %$S" 2;- and )nified Thread Standard& include a
coarse pitch and a fine pitch for each ma1or diameter. (or example,
-
P
2
=-7 belongs to
the )*+ series %)nified *ational +oarse& and
-
P
2
=25 belongs to the )*( series
%)nified *ational (ine&.
! common misconception among people not familiar with engineering or machining
is that the term coarse implies here lower #uality and the term fine implies higher
#uality. The terms when used in reference to screw thread pitch have nothing to do
with the tolerances used %degree of precision& or the amount of craftsmanship, #uality,
or cost. They simply refer to the size of the threads relative to the screw diameter.
+oarse threads can be made accurately, or fine threads inaccurately.
Diameters
The three diameters that characterize
boltHnut threads
There are three characteristic diameters of threadsG major diameter, minor diameter,
and pitch diameterG industry standards specify minimum %min& and maximum %max&
limits for each of these, for all recognized thread sizes. The min limits for external %or
bolt, in $S" terminology&, and the max limits for internal %nut&, thread sizes are there
to ensure that threads do not strip at the tensile strength limits for the parent material.
The min limits for internal, and max limits for external, threads are there to ensure
that the threads fit together.
'a(or diameter
The ma1or diameter of threads is the larger of two extreme diameters delimiting the
height of the thread profile, as a cross=sectional view is ta/en in a plane containing the
axis of the threads. (or a screw, this is its outside diameter. The ma1or diameter of a
nut may not be directly measured, but it may be tested with goHno=go gauges.
The ma1or diameter of external threads is normally smaller than the ma1or diameter of
the internal threads, if the threads are designed to fit together. <ut this re#uirement
alone does not guarantee that a bolt and a nut of the same pitch would fit togetherG the
same re#uirement must separately be made for the minor and pitch diameters of the
threads. <esides providing for a clearance between the crest of the bolt threads and
the root of the nut threads, we must also ensure that the clearances are not so
excessive as to cause the fasteners to fail.
'inor diameter
The basic profile of
all )TS threads is
the same as that of
all IS) metric
screw threads.
"nly the commonly
used values for
:ma1 and ' differ
between the two
standards.
The minor diameter is the lower extreme diameter of the thread. Ma1or diameter
minus minor diameter, divided by two, e#uals the height of the thread. The minor
diameter of a nut is its inside diameter. The minor diameter of a bolt can be measured
with goHno=go gauges or, directly, with an optical comparator.
!s shown in the figure at right, threads of e#ual pitch and angle that have matching
minor diameters, with differing ma1or and pitch diameters, may appear to fit snugly,
but only do so radiallyN threads that have only ma1or diameters matching %not shown&
could also be visualized as not allowing radial movement. The reduced material
condition, due to the unused spaces between the threads, must be minimized so as not
to overly wea/en the fasteners.
&itch diameter
Lariants of snug fit. "nly threads with
matched ':s are truly snug, axially as
well as radially
The pitch diameter %':, or D
2
& of a particular thread, internal or external, is the
diameter of a cylindrical surface, axially concentric to the thread, which intersects the
thread flan/s at e#uidistant points, when viewed in a cross=sectional plane containing
the axis of the thread, the distance between these points being exactly one half the
pitch distance. E#uivalently, a line running parallel to the axis and a distance D
2
away
from it, the 0': line,0 slices the sharp-V form of the thread, having flan/s coincident
with the flan/s of the thread under test, at exactly .56 of its height. 4e have assumed
that the flan/s have the proper shape, angle, and pitch for the specified thread
standard. $t is generally unrelated to the ma1or %D& and minor %D
-
& diameters,
especially if the crest and root truncations of the sharp=L form at these diameters are
un/nown. Everything else being ideal, D
2
, D, D
-
, together, would fully describe the
thread form. Knowledge of ': determines the position of the sharp=L thread form,
the sides of which coincide with the straight sides of the thread flan/sG e.g., the crest
of the external thread would truncate these sides a radial displacement D = D
2
away
from the position of the ': line.
'rovided that there are moderate non=negative clearances between the root and crest
of the opposing threads, and everything else is ideal, if the pitch diameters of a screw
and nut are exactly matched, there should be no play at all between the two as
assembled, even in the presence of positive root=crest clearances. This is the case
when the flan/s of the threads come into intimate contact with one another, before the
roots and crests do, if at all.
3owever, this ideal condition would in practice only be approximated and would
generally re#uire wrench=assisted assembly, possibly causing the galling of the
threads. (or this reason, some alloance, or minimum difference, between the ':s of
the internal and external threads has to generally be provided for, to eliminate the
possibility of deviations from the ideal thread form causing interference and to
expedite hand assembly up to the length of engagement. Such allowances, or
fundamental deviations, as $S" standards call them, are provided for in various
degrees in corresponding classes of fit for ranges of thread sizes. !t one extreme, no
allowance is provided by a class, but the maximum ': of the external thread is
specified to be the same as the minimum ': of the internal thread, within specified
tolerances, ensuring that the two can be assembled, with some looseness of fit still
possible due to the margin of tolerance. ! class called interference fit may even
provide for negative allowances, where the ': of the screw is greater than the ': of
the nut by at least the amount of the allowance.
The pitch diameter of external threads is measured by various methodsG
! dedicated type of micrometer, called a thread mic or pitch mic, which has a L=anvil and
a conical spindle tip, contacts the thread flan/s for a direct reading.
! general=purpose micrometer %flat anvil and spindle& is used over a set of three wires that
rest on the thread flan/s, and a /nown constant is subtracted from the reading. %The wires
are truly gauge pins, being ground to precise size, although 0wires0 is their common
name.& This method is called the 7=wire method. Sometimes grease is used to hold the
wires in place, helping the user to 1uggle the part, mic, and wires into position.
!n optical comparator may also be used to determine ': graphically.
Classes of fit
The way in which male and female fit together, including play and friction, is
classified %categorized& in thread standards. !chieving a certain class of fit re#uires
the ability to wor/ within tolerance ranges for dimension %size& and surface finish.
:efining and achieving classes of fit are important for interchangeability. +lasses
include -, 2, 7 %loose to tight&N ! %external& and < %internal&N and various systems such
as 3 and : limits.
Standardi*ation and interchangeabilit+
To achieve a predictably successful mating of male and female threads and assured
interchangeability between males and between females, standards for form, size, and
finish must exist and be followed. Standardization of threads is discussed below.
Thread depth
Screw threads are almost never made perfectly sharp %no truncation at the crest or
root&, but instead are truncated, yielding a final thread depth that can be expressed as
a fraction of the pitch value. The )TS and $S" standards codify the amount of
truncation, including tolerance ranges.
! perfectly sharp ;5M L=thread will have a depth of thread %0height0 from root to
crest& e#ual to .?;; of the pitch. This fact is intrinsic to the geometry of an e#uilateral
triangleOa direct result of the basic trigonometric functions. $t is independent of
measurement units %inch vs mm&. 3owever, )TS and $S" threads are not sharp
threads. The ma1or and minor diameters delimit truncations on either side of the sharp
L, typically about one eighth of the pitch %expressed with the notation -H?p or .-2.p&,
although the actual geometry definition has more variables than that. This means that
a full %-556& )TS or $S" thread has a height of around .;.p.
Threads can be %and often are& truncated a bit more, yielding thread depths of ;5
percent to F. percent of the .;.p value. (or example, a F. percent thread sacrifices
only a small amount of strength in exchange for a significant reduction in the force
re#uired to cut the thread. The result is that tap and die wear is reduced, the li/elihood
of brea/age is lessened and higher cutting speeds can often be employed.
Truncation is achieved by using a slightly larger tap drill in the case of female threads,
or by slightly reducing the diameter of the threaded area of wor/piece in the case of
male threads, the latter effectively reducing the thread9s ma1or diameter. $n the case of
female threads, tap drill charts typically specify sizes that will produce an
approximate F. percent thread. ! ;5 percent thread may be appropriate in cases where
high tensile loading will not be expected. $n both cases, the pitch diameter is not
affected. The balancing of truncation versus thread strength is similar to many
engineering decisions involving the strength, weight and cost of material, as well as
the cost to machine it.
Taper
Tapered threads are used on fasteners and pipe. ! common example of a fastener with
a tapered thread is a wood screw.
The threaded pipes used in some plumbing installations for the delivery of fluids
under pressure have a threaded section that is slightly conical. Examples are the *'T
and <S' series. The seal provided by a threaded pipe 1oint is created when a tapered
externally threaded end is tightened into an end with internal threads. *ormally a
good seal re#uires the application of a separate sealant in the 1oint, such as thread seal
tape, or a li#uid or paste pipe sealant such as pipe dope, however some threaded pipe
1oints do not re#uire a separate sealant.
Standardi*ation
Standardization of screw
threads has evolved since the
early nineteenth century to
facilitate compatibility
between different
manufacturers and users. The standardization process is still ongoingN in particular
there are still %otherwise identical& competing metric and inch=sized thread standards
widely used.B;C Standard threads are commonly identified by short letter codes %M,
)*+, etc.& which also form the prefix of the standardized designations of individual
threads.
!dditional product standards identify preferred thread sizes for screws and nuts, as
well as corresponding bolt head and nut sizes, to facilitate compatibility between
spanners %wrenches& and other tools.
IS) standard threads
Main articleG IS) metric screw thread
The most common threads in use are the $S" metric screw threads %M& for most
purposes and <S' threads %>, D& for pipes.
These were standardized by the $nternational "rganization for Standardization %$S"&
in -@8F. !lthough metric threads were mostly unified in -?@? by the $nternational
+ongress for the standardization of screw threads, separate metric thread standards
were used in (rance, Dermany, and ,apan, and the Swiss had a set of threads for
watches.
,rass
(rom 4i/ipedia, the free encyclopedia
(or other uses, see ,rass $disambig"ation%.
<rass die, along with
zinc and copper
samples.
<rass lectern with
an eagle. !ttributed to
Aert van Tricht,
Limb"rg
$-etherlands%, c.
-.55.
Brass is an alloy
made of copper
and zincN the
proportions of zinc
and copper can be
varied to create a
range of brasses
with varying
properties.B-C $t is
a substitutional
alloyG atoms of the
two constituents
may replace each
other within the
same crystal
structure.
<y comparison, bronze is principally an alloy of copper and tin.B2C <ronze does not
necessarily contain tin, and a variety of alloys of copper, including alloys with
arsenic, phosphorus, aluminium, manganese, and silicon, are commonly termed
0bronze0. The term is applied to a variety of brasses and the distinction is largely
historical,B7C and modern practice in museums and archaeology is increasingly to
avoid both terms for historical ob1ects in favour of the all=embracing 0copper alloy0.
B8C
<rass is used for decoration for its bright gold=li/e appearanceN for applications where
low friction is re#uired such as loc/s, gears, bearings, door/nobs, ammunition casings
and valvesN for plumbing and electrical applicationsN and extensively in brass musical
instruments such as horns and bells for its acoustic properties. $t is also used in
zippers. <rass is often used in situations where it is important that spar/s not be
struc/, as in fittings and tools around explosive gases.B.C
Contents
- 'roperties
2 Eead content
7 +orrosion=resistant brass for harsh environments
8 Dermicidal and antimicrobial applications
. Season crac/ing
; <rass types
F 3istory
o F.- Early copper zinc alloys
o F.2 <rass ma/ing in the >oman 4orld
o F.7 <rass ma/ing in the medieval period
o F.8 <rass in !frica
o F.. <rass ma/ing in >enaissance and post=medieval Europe
? See also
@ >eferences
-5 <ibliography
-- External lin/s
&roperties
'icrostr"ct"re of
rolled and annealed brass
%855Q magnification&
The malleability and
acoustic properties of
brass have made it the
metal of choice for musical instruments such as the trombone, tuba, trumpet, cornet,
baritone horn, euphonium, tenor horn, and (rench horn which are collectively /nown
as brass instruments. Even though the saxophone is classified as a woodwind
instrument and the harmonica is a free reed aerophone, both are also often made from
brass. $n organ pipes of the reed family, brass strips %called tongues& are used as the
reeds, which beat against the shallot %or beat 0through0 the shallot in the case of a
0free0 reed&. !lthough not part of the brass section, snare drums are also sometimes
made of brass.
<rass has higher malleability than bronze or zinc. The relatively low melting point of
brass %@55 to @85 M+, -;.2 to -F28 M(, depending on composition& and its flow
characteristics ma/e it a relatively easy material to cast. <y varying the proportions of
copper and zinc, the properties of the brass can be changed, allowing hard and soft
brasses. The density of brass is approximately .757 lbHcubic inch, ?.8 to ?.F7 grams
per cubic centimetre.B;C
Today almost @56 of all brass alloys are recycled.BFC <ecause brass is not
ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a
powerful magnet. <rass scrap is collected and transported to the foundry where it is
melted and recast into billets. <illets are heated and extruded into the desired form
and size.
!luminium ma/es brass stronger and more corrosion resistant. !luminium also
causes a highly beneficial hard layer of aluminium oxide %!l
2
"
7
& to be formed on the
surface that is thin, transparent and self=healing. Tin has a similar effect and finds its
use especially in seawater applications %naval brasses&. +ombinations of iron,
aluminium, silicon and manganese ma/e brass wear and tear resistant.B?C
Lead content
To enhance the machinability of brass, lead is often added in concentrations of around
26. Since lead has a lower melting point than the other constituents of the brass, it
tends to migrate towards the grain boundaries in the form of globules as it cools from
casting. The pattern the globules form on the surface of the brass increases the
available lead surface area which in turn affects the degree of leaching. $n addition,
cutting operations can smear the lead globules over the surface. These effects can lead
to significant lead leaching from brasses of comparatively low lead content.B@C
Silicon is an alternative to leadN however, when silicon is used in a brass alloy, the
scrap must never be mixed with leaded brass scrap because of contamination and
safety problems.B-5C
$n "ctober -@@@ the +alifornia State !ttorney Deneral sued -7 /ey manufacturers and
distributors over lead content. $n laboratory tests, state researchers found the average
brass /ey, new or old, exceeded the +alifornia 'roposition ;. limits by an average
factor of -@, assuming handling twice a day.B--C $n !pril 255- manufacturers agreed
to reduce lead content to -..6, or face a re#uirement to warn consumers about lead
content. Keys plated with other metals are not affected by the settlement, and may
continue to use brass alloys with higher percentage of lead content.B-2CB-7C
!lso in +alifornia, lead=free materials must be used for 0each component that comes
into contact with the wetted surface of pipes and pipe fittings, plumbing fittings and
fixtures.0 "n ,anuary -, 25-5, the maximum amount of lead in 0lead=free brass0 in
+alifornia was reduced from 86 to 5.2.6 lead. The common practice of using pipes
for electrical grounding is discouraged, as it accelerates lead corrosion.B-8CB-.C
Corrosion.resistant brass for harsh
environments
<rass sampling coc/ with
stainless steel handle.
The so=called
dezincification resistant
%:R> or :>& brasses,
sometimes referred to as +> %corrosion resistant& brasses, are used where there is a
large corrosion ris/ and where normal brasses do not meet the standards. !pplications
with high water temperatures, chlorides present, or deviating water #ualities %soft
water& play a role. :R>=brass is excellent in water boiler systems. This brass alloy
must be produced with great care, with special attention placed on a balanced
composition and proper production temperatures and parameters to avoid long=term
failures.
Germicidal and antimicrobial applications
Main articleG Antimicrobial copper.allo+ to"ch s"rfaces
See alsoG Antimicrobial properties of copper and Copper allo+s in
a/"ac"lt"re
The copper in brass ma/es brass germicidal. :epending upon the type and
concentration of pathogens and the medium they are in, brass /ills these
microorganisms within a few minutes to hours of contact.B-;CB-FCB-?C
The bactericidal properties of brass have been observed for centuries and were
confirmed in the laboratory in -@?7.B-@C Subse#uent experiments by research groups
around the world reconfirmed the antimicrobial efficacy of brass, as well as copper
and other copper alloys %see !ntimicrobial copper=alloy touch surfaces&.B-;CB-FCB-?C
Extensive structural membrane damage to bacteria was noted after being exposed to
copper.
$n 255F, ).S. :epartment of :efenseSs Telemedicine and !dvanced Technology
>esearch +enter %T!T>+& began to study the antimicrobial properties of copper
alloys, including four brasses %+?F;-5, +;@755, +2;555, +8;855& in a multi=site
clinical hospital trial conducted at the Memorial Sloan=Kettering +ancer +enter %*ew
Kor/ +ity&, the Medical )niversity of South +arolina, and the >alph 3. ,ohnson L!
Medical +enter %South +arolina&.B25CB2-C +ommonly touched items, such as bed
rails, over=the=bed tray tables, chair arms, nurse9s call buttons, $L poles, etc. were
retrofitted with antimicrobial copper alloys in certain patient rooms %i.e., the
IcopperedJ rooms& in the $ntensive +are )nit %$+)&. Early results disclosed in 25--
indicate that the coppered rooms demonstrated a @F6 reduction in surface pathogens
versus the non=coppered rooms. This reduction is the same level achieved by
IterminalJ cleaning regimens conducted after patients vacate their rooms.
(urthermore, of critical importance to health care professionals, the preliminary
results indicated that patients in the coppered $+) rooms had a 85.86 lower ris/ of
contracting a hospital ac#uired infection versus patients in non=coppered $+) rooms.
B25CB22CB27C The ).S. :epartment of :efense investigation contract, which is
ongoing, will also evaluate the effectiveness of copper alloy touch surfaces to prevent
the transfer of microbes to patients and the transfer of microbes from patients to touch
surfaces, as well as the potential efficacy of copper=alloy based components to
improve indoor air #uality.
$n the ).S., the Environmental 'rotection !gency regulates the registration of
antimicrobial products. !fter extensive antimicrobial testing according to the
!gencySs stringent test protocols, 7.. copper alloys, including many brasses, were
found to /ill more than @@.@6 of methicillin=resistant Staphylococcus aureus
%M>S!&, !" coli "-.FG3F, Pseudomonas aeruginosa, Staphylococcus aureus,
!nterobacter aerogenes, and vancomycin=resistant !nterococci %L>E& within two
hours of contact.B-;CB28C *ormal tarnishing was found not to impair antimicrobial
effectiveness.
!ntimicrobial tests have also revealed significant reductions of M>S! as well as two
strains of epidemic M>S! %EM>S!=- and EM>S!=-;& on brass %+28555 with ?56
+u& at room temperature %22 M+& within three hours. +omplete /ills of the pathogens
were observed within 8
-
P
2
hours. These tests were performed under wet exposure
conditions. The /ill timeframes, while impressive, are nevertheless longer than for
pure copper, where /ill timeframes ranged between 8. to @5 minutes.B-?C
! novel assay that mimics dry bacterial exposure to touch surfaces was developed
because this test method is thought to more closely replicate real world touch surface
exposure conditions. $n these conditions, copper alloy surfaces were found to /ill
several million +olony (orming )nits of !scherichia coli within minutes.B2.C This
observation, and the fact that /ill timeframes shorten as the percentage of copper in an
alloy increases, is proof that copper is the ingredient in brass and other copper alloys
that /ills the microbes.B2;C
The mechanisms of antimicrobial action by copper and its alloys, including brass, is a
sub1ect of intense and ongoing investigation.B-FCB2.CB2FC $t is believed that the
mechanisms are multifaceted and include the followingG -& 'otassium or glutamate
lea/age through the outer membrane of bacteriaN 2& "smotic balance disturbancesN 7&
<inding to proteins that do not re#uire or utilize copperN 8& "xidative stress by
hydrogen peroxide generation.
>esearch is being conducted at this time to determine whether brass, copper, and other
copper alloys can help to reduce cross contamination in public facilities and reduce
the incidence of nosocomial infections %hospital ac#uired infections& in healthcare
facilities.
!lso, owing to its antimicrobialHalgaecidal properties that prevent biofouling, in
con1unction with its strong structural and corrosion=resistant benefits for marine
environments, brass alloy netting cages are currently being deployed in commercial=
scale a#uaculture operations in !sia, South !merica, and the )S!.
Season crac0ing
+rac/ing in
brass
caused by
ammonia
attac/
<rass is
susceptible to stress corrosion crac/ing, especially from ammonia or substances
containing or releasing ammonia. The problem is sometimes /nown as season
crac/ing after it was first discovered in brass cartridge cases used for rifle ammunition
during the -@25s in the $ndian !rmy. The problem was caused by high residual
stresses from cold forming of the cases during manufacture, together with chemical
attac/ from traces of ammonia in the atmosphere. The cartridges were stored in
stables and the ammonia concentration rose during the hot summer months, thus
initiating brittle crac/s. The problem was resolved by annealing the cases, and storing
the cartridges elsewhere.
,rass t+pes
+lass +opper Rinc *otes
%6& %6&
!lpha brasses T;. U7. !lpha brasses are malleable, can be wor/ed cold, and are used
in pressing, forging, or similar applications. They contain only
one phase, with
face.centered c"bic

cr+stal
str"ct"re
.
!lpha=beta
brasses
..V;. 7.V8. !lso called duplex brasses. Suited for hot wor/ing. $t contains
both W and X9 phaseN the X9=phase is
bod+.centered c"bic

and is harder and stronger than W. !lpha=beta brasses are usually
wor/ed hot.
<eta brasses .5V.. 8.V.5 +an only be wor/ed hot, and are harder, stronger, and suitable
for casting.
4hite brass U.5 T.5 Too brittle for general use. The term may also refer to certain
types of
nic0el silver
alloys as well as +u=Rn=Sn alloys
with high proportions %typically 856Y& of tin andHor zinc, as
well as predominantly zinc casting alloys with copper additive.
<rass alloys
!lloy name +opper
%6&
Rinc
%6&
"ther *otes
!dmiralty brass ;@ 75 -6 tin +ontains -6 tin to
inhibit
de*incificati
on
in many
environments.
!ich9s alloy ;5.;; 7;..? -.526 tin, -.F86 iron :esigned for use
in marine service
owing to its
corrosion
resistance,
hardness and
toughness. !
characteristic
application is to
the protection of
ships9 bottoms, but
more modern
methods of
cathodic protection
have rendered its
use less common.
$ts appearance
resembles that of
gold.
1234
!luminium brass aluminum +ontains
<rass alloys
!lloy name +opper
%6&
Rinc
%6&
"ther *otes
al"mini"m
,
which improves its
corrosion
resistance. $t is
used for seawater
service.
1254
!rsenical brass
arsenic
, fre#uently
al"min"m
)sed for boiler
fireboxes
.
+artridge brass F5 75 Dood
cold
wor0ing

properties. )sed
for ammunition
cases.
+ommon brass 7F !lso called rivet
brass. +heap and
standard for cold
wor/ing.
:R> brass arsenic :ezincification
resistant brass with
a small percentage
of arsenic.
Gilding metal
@. . Softest type of
brass commonly
available. Dilding
metal is typically
used for
ammunition bullet
01ac/ets0, e.g.,
f"ll metal
(ac0et
bullets.
3igh brass ;. 7. 3as a high
tensile
strength
and is
used for
springs
,
screws
, and
rivets
.
Eeaded brass lead !n alpha=beta
brass with an
addition of
lead
.
$t has excellent
<rass alloys
!lloy name +opper
%6&
Rinc
%6&
"ther *otes
machinability.
Eead=free brass U5.2.6 lead :efined by
+alifornia
!ssembly <ill !<
-@.7 contains 0not
more than 5.2.
percent lead
content0.
1674
Eow brass ?5 25 3as a light golden
color and excellent
ductilityN it is used
for flexible metal
hoses and metal
bellows
.
Manganese brass F5 2@ -.76
manganese
Most notably used
in ma/ing
golden
dollar
coins in
the )nited States.
1894
'"nt* metal
;5 85 traces of iron )sed as a lining on
boats.
*aval brass .@ 85 -6 tin Similar to
admiralty brass.
*ic/el brass F5 28.. ...6 nic/el )sed to ma/e
pound coins in the
po"nd
sterling

currency.
-ordic gold
?@ . .6 aluminium, -6 tin )sed in -5, 25, and
.5 cents
e"ro
coins
.
'rince9s metal F. 2. ! type of alpha
brass. :ue to its
yellow color, it is
used as an
imitation of gold.
1864
!lso called
'rince >upert9s
metal, the alloy
<rass alloys
!lloy name +opper
%6&
Rinc
%6&
"ther *otes
was named after
&rince :"pert
of the :hine
.
>ed brass ?. . .6 tin, .6 lead <oth an !merican
term for the
copper=zinc=tin
alloy /nown as
g"nmetal
, and an
alloy which is
considered both a
brass and a bronze.
18241884
>ed
brass is also an
alternative name
for copper alloy
+27555, which is
composed of -8V
-;6 zinc, 5.5.6
iron and lead, and
the remainder
copper.
1874
$t
may also refer to
o"nce metal
,
another copper=
zinc=tin alloy.
>ich low brass,
Tombac
.V25 "ften used in
1ewelry
applications.
Tonval brass lead !lso called
+4;-F* or
+R-22 or "T.?. $t
is not
recommended for
seawater use,
being susceptible
to dezincification.
18;418<4
Kellow brass ;F 77 !n !merican term
for 776 zinc brass.
Histor+
!lthough forms of brass have been in use since prehistory,B7FC its true nature as a
copper=zinc alloy was not understood until the post medieval period because the zinc
vapor which reacted with copper to ma/e brass was not recognised as a metal.B7?C
The King ,ames <ible ma/es many references to 0brass0.B7@C The Sha/espearean
English form of the word 9brass9 can mean any bronze alloy, or copper, rather than the
strict modern definition of brass.Bcitation neededC The earliest brasses may have been
natural alloys made by smelting zinc=rich copper ores.B85C <y the >oman period brass
was being deliberately produced from metallic copper and zinc minerals using the
cementation process and variations on this method continued until the mid=-@th
century.B8-C $t was eventually replaced by speltering, the direct alloying of copper and
zinc metal which was introduced to Europe in the -;th century.B85C
=arl+ copper *inc allo+s
$n 4est !sia and the Eastern Mediterranean early copper zinc alloys are now /nown
in small numbers from a number of third Millennium <+ sites in the !egean, $ra#, the
)nited !rab Emirates, Kalmy/ia, Tur/menistan and Deorgia and from 2nd
Millennium <+ sites in 4est $ndia, )zbe/istan, $ran, Syria, $ra# and $srael.B82C
3owever, isolated examples of copper=zinc alloys are /nown in +hina from as early
as the .th Millennium <+.B87C
The compositions of these early 0brass0 ob1ects are very variable and most have zinc
contents of between .6 and -.6 wt which is lower than in brass produced by
cementation.B88C These may be 0natural alloys0 manufactured by smelting zinc rich
copper ores in redox conditions. Many have similar tin contents to contemporary
bronze artefacts and it is possible that some copper=zinc alloys were accidental and
perhaps not even distinguished from copper.B88C 3owever the large number of
copper=zinc alloys now /nown suggests that at least some were deliberately
manufactured and many have zinc contents of more than -26 wt which would have
resulted in a distinctive golden color.B88CB8.C
<y the ?thVFth century <+ !ssyrian cuneiform tablets mention the exploitation of the
0copper of the mountains0 and this may refer to 0natural0 brass.B8;C #reichal$os, the
!ncient Dree/ translation of this term, was later adapted to the Eatin aurichalcum
meaning 0golden copper0 which became the standard term for brass.B8FC $n the 8th
century <+ 'lato /new oreichal$os as rare and nearly as valuable as goldB8?C and
'liny describes how aurichalcum had come from +ypriot ore deposits which had been
exhausted by the -st century !:.B8@C
,rass ma0ing in the :oman >orld
Fth=century 'ersian ewer in brass with
copper inlay
:uring the later part of first
millennium <+ the use of brass spread across a wide geographical area from
<ritainB.5C and SpainB.-C in the west to $ran, and $ndia in the east.B.2C This seems to
have been encouraged by exports and influence from the Middle=East and eastern
Mediterranean where deliberate production of brass from metallic copper and zinc
ores had been introduced.B.7C The 8th century <+ writer Theopompus, #uoted by
Strabo, describes how heating earth from !ndeira in Tur/ey produced 0droplets of
false silver0, probably metallic zinc, which could be used to turn copper into
oreichal/os.B.8C $n the -st century <+ the Dree/ :ioscorides seems to have
recognised a lin/ between zinc minerals and brass describing how +admia %zinc
oxide& was found on the walls of furnaces used to heat either zinc ore or copper and
explaining that it can then be used to ma/e brass.B..C
<y the first century <+ brass was available in sufficient supply to use as coinage in
'hrygia and <ithynia,B.;C and after the !ugustan currency reform of 27 <+ it was
also used to ma/e >oman dupondii and sestertii.B.FC The uniform use of brass for
coinage and military e#uipment across the >oman world may indicate a degree of
state involvement in the industry,B.?CB.@C and brass even seems to have been
deliberately boycotted by ,ewish communities in 'alestine because of its association
with >oman authority.B;5C
<rass was produced by the cementation process where copper and zinc ore are heated
together until zinc vapor is produced which reacts with the copper. There is good
archaeological evidence for this process and crucibles used to produce brass by
cementation have been found on >oman period sites including QantenB;-C and
*iddaB;2C in Dermany, Eyon in (ranceB;7C and at a number of sites in <ritain.B;8C
They vary in size from tiny acorn sized to large amphorae li/e vessels but all have
elevated levels of zinc on the interior and are lidded.B;7C They show no signs of slag
or metal prills suggesting that zinc minerals were heated to produce zinc vapor which
reacted with metallic copper in a solid state reaction. The fabric of these crucibles is
porous, probably designed to prevent a buildup of pressure, and many have small
holes in the lids which may be designed to release pressureB;7C or to add additional
zinc minerals near the end of the process. :ioscorides mentioned that zinc minerals
were used for both the wor/ing and finishing of brass, perhaps suggesting secondary
additions.B;.C
<rass made during the early >oman period seems to have varied between 256 to 2?6
wt zinc.B;;C The high content of zinc in coinage and brass ob1ects declined after the
first century !: and it has been suggested that this reflects zinc loss during recycling
and thus an interruption in the production of new brass.B;FC 3owever it is now
thought this was probably a deliberate change in compositionB;?C and overall the use
of brass increases over this period ma/ing up around 856 of all copper alloys used in
the >oman world by the 8th century !:.B;@C
,rass ma0ing in the medieval period
,aptism
of
Christ on
the -2th=
century
baptismal font at St ,artholomew?s Ch"rch Li@ge
Eittle is /nown about the production of brass during the centuries immediately after
the collapse of the >oman Empire. :isruption in the trade of tin for bronze from
4estern Europe may have contributed to the increasing popularity of brass in the east
and by the ;thVFth centuries !: over @56 of copper alloy artefacts from Egypt were
made of brass.BF5C 3owever other alloys such as low tin bronze were also used and
they vary depending on local cultural attitudes, the purpose of the metal and access to
zinc, especially between the $slamic and <yzantine world.BF-C +onversely the use of
true brass seems to have declined in 4estern Europe during this period in favour of
gunmetals and other mixed alloysBF2C but by about -555 brass artefacts are found in
Scandinavian graves in Scotland,BF7C brass was being used in the manufacture of
coins in *orthumbriaBF8C and there is archaeological and historical evidence for the
production of brass in DermanyBF.C and The Eow +ountries,BF;C areas rich in
calamine ore.
These places would remain important centres of brass ma/ing throughout the
medieval period,BFFC especially :inant. <rass ob1ects are still collectively /nown as
dinanterie in (rench. The baptismal font at St <artholomew9s +hurch, EiZge in
modern <elgium %before ---F& is an outstanding masterpiece of >omanes#ue brass
casting, though also often described as bronze. The metal of the early -2th=century
Dloucester +andlestic/ is unusual even by medieval standards in being a mixture of
copper, zinc, tin, lead, nic/el, iron, antimony and arsenic with an unusually large
amount of silver = between 22..6 in the base and ..F;6 in the pan below the candle.
The proportions of this mixture may suggest that the candlestic/ was made from a
hoard of old coins, probably Eate >oman.BF?C Eatten is a term for decorative borders
and similar ob1ects cut from sheet metal, whether of brass or bronze. !#uamaniles
were typically made in brass in both the European and $slamic worlds.
<rass a/"amanile
from Lower
Saxon+, Dermany, c.
-2.5
The cementation
process continued
to be used but
literary sources
from both Europe and the $slamic world seem to describe variants of a higher
temperature li#uid process which too/ places in open=topped crucibles.BF@C $slamic
cementation seems to have used zinc oxide /nown as tutiya or tutty rather than zinc
ores for brass ma/ing resulting in a metal with lower iron impurities.B?5C ! number of
$slamic writers and the -7th century $talian Marco 'olo describe how this was
obtained by sublimation from zinc ores and condensed onto clay or iron bars,
archaeological examples of which have been identified at Kush in $ran.B?-C $t could
then be used for brass ma/ing or medicinal purposes. $n -5th century Kemen al=
3amdani described how spreading al=iglimiya, probably zinc oxide, onto the surface
of molten copper produced tutiya vapor which then reacted with the metal.B?2C The
-7th century $ranian writer al=Kashani describes a more complex process whereby
tutiya was mixed with raisins and gently roasted before being added to the surface of
the molten metal. ! temporary lid was added at this point presumably to minimise the
escape of zinc vapor.B?7C
$n Europe a similar li#uid process in open=topped crucibles too/ place which was
probably less efficient than the >oman process and the use of the term tutty by
!lbertus Magnus in the -7th century suggests influence from $slamic technology.B?8C
The -2th century Derman mon/ Theophilus described how preheated crucibles were
one sixth filled with powdered calamine and charcoal then topped up with copper and
charcoal before being melted, stirred then filled again. The final product was cast,
then again melted with calamine. $t has been suggested that this second melting may
have ta/en place at a lower temperature to allow more zinc to be absorbed.B?.C
!lbertus Magnus noted that the 0power0 of both calamine and tutty could evaporate
and described how the addition of powdered glass could create a film to bind it to the
metal.B?;C Derman brass ma/ing crucibles are /nown from :ortmund dating to the
-5th century !: and from Soest and Schwerte in 4estphalia dating to around the
-7th century confirm Theophilus9 account, as they are open=topped, although ceramic
discs from Soest may have served as loose lids which may have been used to reduce
zinc evaporation, and have slag on the interior resulting from a li#uid process.B?FC
,rass in Africa
-2th century 0,ron*e Head from
Ife0, actually of 0heavily leaded zinc=
brass0
Some of the most famous ob1ects
in !frican art are the lost wax
castings of 4est !frica, mostly
from what is now *igeria, produced first by the Kingdom of $fe and then the <enin
Empire. Though normally described as 0bronzes0, the <enin <ronze pla#ues, now
mostly in the <ritish Museum and other 4estern collections, and the large portrait
heads such as the $fe 3ead of 0heavily leaded zinc=brass0 and the <ronze 3ead of
[ueen $dia, both also <ritish Museum, are better described as brass, though of
variable compositions.B??C 4or/ in brass or bronze continued to be important in
<enin art and other 4est !frican traditions such as !/an goldweights, where the
metal was regarded as a more valuable material than in Europe.
,rass ma0ing in :enaissance and post.medieval ="rope
The >enaissance saw important changes to both the theory and practice of
brassma/ing in Europe. <y the -.th century there is evidence for the renewed use of
lidded cementation crucibles at Rwic/au in Dermany.B?@C These large crucibles were
capable of producing c.25 /g of brass.B@5C There are traces of slag and pieces of metal
on the interior. Their irregular composition suggesting that this was a lower
temperature not entirely li#uid process.B@-C The crucible lids had small holes which
were bloc/ed with clay plugs near the end of the process presumably to maximise
zinc absorption in the final stages.B@2C Triangular crucibles were then used to melt the
brass for casting.B@7C
-;th=century technical writers such as <iringuccio, Erc/er and !gricola described a
variety of cementation brass ma/ing techni#ues and came closer to understanding the
true nature of the process noting that copper became heavier as it changed to brass
and that it became more golden as additional calamine was added.B@8C Rinc metal was
also becoming more commonplace <y -.-7 metallic zinc ingots from $ndia and +hina
were arriving in Eondon and pellets of zinc condensed in furnace flues at the
>ammelsberg in Dermany were exploited for cementation brass ma/ing from around
-..5.B@.C
Eventually it was discovered that metallic zinc could be alloyed with copper to ma/e
brassN a process /nown as spelteringB@;C and by -;.F the Derman chemist ,ohann
Dlauber had recognised that calamine was 0nothing else but unmeltable zinc0 and that
zinc was a 0half ripe metal.0B@FC 3owever some earlier high zinc, low iron brasses
such as the -.75 4ightman brass memorial pla#ue from England may have been
made by alloying copper with %inc and include traces of cadmium similar those found
in some zinc ingots from +hina.B@;C
3owever the cementation process was not abandoned and as late as the early -@th
century there are descriptions of solid=state cementation in a domed furnace at around
@55V@.5 M+ and lasting up to -5 hours.B@?C The European brass industry continued to
flourish into the post medieval period buoyed by innovations such as the -;th century
introduction of water powered hammers for the production of battery wares.B@@C <y
-..@ the Dermany city of !achen alone was capable of producing 755,555 cwt of
brass per year.B@@C !fter several false starts during the -;th and -Fth centuries the
brass industry was also established in England ta/ing advantage of abundant supplies
of cheap copper smelted in the new coal fired reverberatory furnace.B-55C $n -F27
<ristol brass ma/er *ehemiah +hampion patented the use of granulated copper,
produced by pouring molten metal into cold water.B-5-C This increased the surface
area of the copper helping it react and zinc contents of up to 776 wt were reported
using this new techni#ue.B-52C
$n -F7? *ehemiah9s son 4illiam +hampion patented a techni#ue for the first
industrial scale distillation of metallic zinc /nown as distillation per descencum or
0the English process.0B-57CB-58C This local zinc was used in speltering and allowed
greater control over the zinc content of brass and the production of high=zinc copper
alloys which would have been difficult or impossible to produce using cementation,
for use in expensive ob1ects such as scientific instruments, cloc/s, brass buttons and
costume 1ewellery.B-5.C 3owever +hampion continued to use the cheaper calamine
cementation method to produce lower=zinc brassB-5.C and the archaeological remains
of bee=hive shaped cementation furnaces have been identified at his wor/s at
4armley.B-5;C <y the mid=to=late -?th century developments in cheaper zinc
distillation such as ,ohn=,a#ues :ony9s horizontal furnaces in <elgium and the
reduction of tariffs on zincB-5FC as well as demand for corrosion=resistant high zinc
alloys increased the popularity of speltering and as a result cementation was largely
abandoned by the mid=-@th century.B-5?C
Screw=threading machine.
)S -5;?-2; !
$mages%-&

:escription %"+> text may contain errors&
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v 'atented ,uly 22, -@-7.
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Specification of Eetters 'atent.
'atented ,uly 22, -@-7.
To all EHA,53E it may concern <e it /nown that we, Exnnnnon +. 3!M= $E9l"* and
,osnrn !. 3nmnnons, citizens of the )nited States, residing at (lint, in the count - of
Denesee and State of ll lichiean have invented certain new and useful -mprovcments
in Screw=Threading h lachinesN and we do hereby declare the following to be a full,
clear, and, exact description of the invention, such as will enable others s/illed in the
art to which it appertains to ma/e and use the same.
T his invention relates to scrim=threading machines, and it more yntrticularly relates
to an improved tension=feed mechanism for regulating the pressure of the die upon the
stud or screw which is being threaded.
4hen threading a stud or screw with a machine in which the ordinary force=feed is i
employed for n9ioving the die longitudinally of the screw or stud, it is essential that
the longitudinal movement of the shaft which carries the die is commensurate with the
pitch of the screw=thrcau9l to be out. $f the longitudinal movement is greater or less, or
if the rotary movement of the screw becomes greater or less than is connnensurate,
then the threads will either be marred or demolishedN therefore, many of the screws
are imperfect and many others are rendered en tirely worthless because of some of the
numorons defects or inaccuracies which. result from the slipping of belts, iiniccurate
ad1ustment, lost motion, and many other things which are li/ely to occur and affect
the relative speeds which are essential in the priuluction of perfect screw threads, and
therefore,an ob1ect of the invention is to provide an improved and simplified
mechanism of this character whereby a single fo-9ceGt9eed member may be employed
in lieu of the large number of forcefeed devices whicu have heretofore been found
necessary in accomplishing the same general result that is accomplished by this
invention.
!nother ob1ect of the invention is to provide a device of this character which obviates
and avoids the unsatisfactory results which attend other screw=threading ma chines
when certain parts thereof become worn, or when the belts or other transmis sion
gears slip or otherwise operate imperfectly.
!nother ob1ect of the invention is to pro vide a mechanism of this character which
may be #uic/ly and easily ad1usted, for regulating the tension, preparatory to cutting
screws of different sizes and of different materials.
"ther ob1ects and advantages may be re cited hereinafter and in the claims.
$n th e accompanying drawings which supplement this specification, (igure - is a side
elevation view of our improved tension=feed mechanism, and, (ig. 2 is a detail view
of a cam which may be used in connection with the mechanism shown in (ig. -.
>eferring to these drawings, in which similar reference characters indicate the same
parts throughout the several views, the stud or screw . is held by the usual or any
preferred form of chuc/ ;, carried by a spindle F, which rotatable within the bar ? and
adapted to be actuated by means of a cone pulley @ and a belt -5, or by other proper
means. ! reciprocatory shaft -- is slidably seated in the bearings -@. ! collar -7 is
ad1ustably seated on the shaft -- by means of a set=screw --. The collar or spring seat
element -7 has a depending extension or arm -. which is slidably engaged with a
guide bar -;, carried by the posts which support the bearings -2N so that the shaft --
may be moved longitudinally with relation to the shaft -; but may not be retated. !
collar -F is slid=ably seated on the shaft --. and has a depending arm -? which
slidably engaged with the shaft -;. ! stud or pivot -@ extends laterally from the arm
-? and has a roller 25 1ournaled thereon.
! spring 2- is seated on the shaft -- and bears against the collars -7 and -F, so as to
separate said collars and exert a tension which tends to separate them when the are
forced into proximity. ! screw or stud 22 is secured to the shaft -- and coacts with the
stud -=- and collars -7 and -F for pressing the spring between said collars and for
limiting the space which separates the col lars. !n ordinary screw=threading die is
carried by the shaft --, as indicated at 27. The die is removably secured to the shaft
--, and may be replaced by another die when another screw or stud of a ditferent size
or different pitch is to be threaded. ! cam 2=- engages with the roller 25, and this cam
may be rotated by any proper means, so as to reciprocate the shaft --, through the
medium of the members -7, 2-, -F, -?, -@ and 25.
$n operation, the die 27 is carried forward against the stud ., as described, and the
relative speeds are regulated so that the spindle -.- is carried forward at a slightly
higher speed than it would be carried by the rota tion of the threads, if said threads
constituted the transmission means of the shaft, therefore, the forward or leftward
movement of the shaft -- is slightly retarded by its contact with the stud ., while the
cam 28 continues to positively force the arm -? and collar -A forward. $t will be seen
that this will result in compressing the spring 2-, and thereby exert=ing a tension upon
the shaft -- which is sufficient to cause the die 27 to ta/e hold of the stud and cut the
thread thereof, but is not sutlicient to feed the die upon the threads with undue
rapidity, and thereby mar or demolish the threads, as sometimes occurs with screw=
threading machines having a force=feed only.
lLhen a screw of greater pitch is to be threaded, the collar -7 may be ad1usted on the
shaft -- so as to diminish the distance between the collars l7 and -F, and thereby
increase the tension of the spring 2-.
^Lhile we have shown a cam of ordinary construction for reciprocating the shaft --, it
is to be understood that we may employ any cam of ordinary and suitable
construction, and while we do not contemplate using a. single cam for all of the
different sizes of screws that may be out upon this machine, we greatly reduce the
number of cams which are necessary. (or instance, we may employ one cam for
cutting all threads from ll to 26 pitch, and replace this cam with one of a larger size
for cutting all threads from 28G to 78, where the screws are longer.
<y means of this improved tension=feed mechanism, we not only improve the #uality
of the screws, but we greatly increase the #uantity, or number produced, by effecting a
great saving of time in eliminating the defects which have hitherto attended this
portion of the former machine, which was the same in all respects as. the one here
illustrated, except that the resilient tensioning device was absent. <y the present
improvement we have increased our output from ?,555 to -6,555 screws per day.
Therefore, it will be seen that we have provided a mechanism of this character which
is fully capable of attaining the foregoing ob1ects, in a. thoroughly practical and
efficient manner.
4e do not limit our invention to the exact details of construction, combination and
arrangement of parts, as herewith illustrated and described, but our invention may
only be limited by a reasonable interpretation of the claims.
-. $n combination, a screw=cutting die, a reciprocatable shaft carrying the die, a collar
ad1ustably secured 5-- the shaft, a second collar slidably secured on the shaft, a
compressible spring on the shaft between the collars, and means for sliding the second
collar 5-- the shaft against the action of said spring to exert a yielding pressure upon
the member to be screw threaded.
2. $n combination, a screw=cutting die, a. reciprocatable shaft, a collar ad1ustably
secured on the shaft and having an arm extending therefrom, a guide bar parallel with
said shaft and being slidably engaged with said arm, a second collar slidably seated on
the shaft and having an arm extending therefrom and in slidable engagement with said
guide bar, a spring compressed between the collars, and means coacting with the
second said arm for sliding the second said collar on said shaft against the action of
said spring and coacting therewith for sliding said shaft and causing said die to exert
ayielding pressure upon a member to be screw=threaded.
$n testimony whereof we have signed our names to this specification in the presence
of two subscribing witnesses.