The balance used in the rolling room of the Royal Mint is specially
adapted for the purpose. Such a balance, as already noticed, must be
accurate, as must also all the balances used in the Mint; but this
balance requires an arrangement by which the pans can be released
from the beam and held firmly while being loaded. Mr. S. R. Short has
been peculiarly happy in effecting this object, as will be seen by
reference to the steel engraving, which exhibits a fine illustration
of Mr. Short’s balance. The raising of the handle A causes the partial
revolution of the cam B—represented by dotted lines—and this, as it
diminishes, releases the lever C, which, by the rods D acting on the
point E, permits the approach of the joints on the rods F towards the
centre. The rods F work on a centre fixed beneath the table on which
the balance stands, so that the closing of their one end causes the
opening of the other. Thus the claws G recede from the wedges H, upon
which they had been fastened, and so release the pan, for the claws act
simply as a man’s hand would act in fixing the pan while it is being
loaded. Immediately upon the opening of the claws another action takes
place by the continued movement of the handle A, which causes the cam
I to rotate upon the friction roller J, affixed to a lever proceeding
from the shaft K, which at L is cut with eccentric bearings, so that
by the partial revolution of K, caused by the pressure of I upon J,
the series of supports M sink downwards from the pans N, thus obliging
the pans, with the rods which support them, to be suspended from the
supports S, which rest on the frame R. So soon as the pans are thus
suspended, the continued motion of the handle A causes the cam O to
permit the falling of the lever P, which at Q supports upon a friction
roller the iron framework R. This framework terminates upwards at the
points near S in sugar-loaf cones of gun-metal, which are intended
to relieve the knife-edges of the beam from the pressure of their
planes while the beam T is out of use, or while it is being loaded,
for at these times the knife-edges would become seriously damaged.
By the lowering of the frame R the centre knife-edge U is permitted
to rest on its plane of steel _c_, which is beautifully bedded on an
arch of gun-metal, as will be seen if the enlarged representation of
this part, and which is shown to the right, be examined. In fact, the
steel plane _c_ is secured by wedges exactly shaped to it, but for the
sake of illustration these wedges have been replaced in the enlarged
portion of the engraving by upright pillars shown against _c_, with
screws travelling through them, and intended to fix _c_ rigidly in a
given position. At the same instant that U comes into rest upon _c_,
the knife-edges V at the ends of the beam T receive the planes W, so
that the beam has now to support the weight of the matter placed in
the scale-pans, and at this time is determined the actual weight of
whatever that matter may be. The weigher, by an indicator suspended
from the beam at X, reads the oscillations of the beam on an ivory
plate at Y. At the time of weighing, the beam with its dependents
is carried by the four-legged frame of iron _b_. The frame R passes
through friction rollers of brass at _d_, which rollers maintain it in
its relative position to the beam. The weighing having been determined,
the handle A is reversed, and the beam is placed at rest; but the
vibration of the machinery in the rolling room causes a continuous
chatter of the knife-edges V against the planes W, therefore at each
end of the beam a small screw Z is made just to touch the lower edge of
the beam when it is at rest. Final adjustments which are very minute
may be arranged by _f_; while the box _e_ on the pan against G is
intended to receive small pieces of lead, which are used to compensate
for the loss by the wearing of the pans. The shaft K is supported from
the table by _a_. The beam of the balance represented in the steel
engraving measures 48·00 inches from knife-edge to knife-edge; that
is to say, it measures 24·00 inches from the centre knife-edge to the
knife-edge at either end. Mr. S. R. Short has made for the rolling
room another balance for weighing silver, and as it differs in some
important details, it is deemed wise to demonstrate those alterations
in Fig. 3, where the supporting frame R will be seen to carry three
upright pillars S¹, S², S³. The pillars S¹ and S³ are represented as
being placed on the farther side of the beam, which at those parts
is broken away, that the pieces of steel against which the pillars
are made to touch may be seen. S² touches against one of these pieces
of steel near the centre knife-edge U, and in front of the beam. The
pillar S² terminates in a point, which passes into an inverted cone,
while the point of S³ is made to pass into an inverted =V=, so that
when the beam is raised by these pillars from its centre knife-edge, S²
obliges it to take a specific position with regard to its distance from
the centre of the plane on which its centre knife-edge rests, and S³
causes it to take a perfectly parallel line. S¹ is simply a plane which
rises against a plane and steadies the other end of the beam, which by
this arrangement stands as on a tripod, and is, therefore, prevented
from moving, and in addition has its knife-edge invariably placed upon
the same part of the plane at each time of weighing, while the frame R,
by its continued lowering, drops the planes with equal accuracy on the
end knife-edges V.
[Illustration: Fig 3.—Short’s Plan for Levelling a Beam.]
[Illustration: Fig. 4.—Breaking-down Mill.]
The sovereign bars having been weighed by the officer, and given by
him to his men, are wrought in sets of twenty; each set is called
a _batch_, and each bar in the batch undergoes precisely the same
process. The bar is passed into the opening A of the breaking-down
mill Fig. 4, where it receives a considerable compression, for the
rollers B, seizing its end, drag it forward, while they roll back and
retard the progress of that part of the bar which is not between them.
The result is that the bar is lengthened, but not widened materially,
so that length is gained at the expense of the thickness, which is
regulated by the distance between the rollers. The rollers are driven
by shafts and adjusting couplings C, which are themselves driven by the
wheels D. The distance between the rollers is determined by the action
of the lever E′, which, by the endless wheels on its axle at E fitting
into geared wheels, gives motion to powerful screws shown at F, which
terminate in cups on the upper part of the upper brasses of the rollers
B, as may be seen at G. The upper brasses are kept always against the
ends of the screws by weights which are beneath the mill, but from
which levers and rods terminate at the lower part of the upper brasses,
at about the position indicated by I, so that the upper roller has
motion either upwards or downwards at pleasure, but the motion upwards
is arrested by the powerful screws F, and this point once determined
by the reading of the scale H, is fixed by the clamp J. The thickness,
therefore, of each bar in a batch is determined within certain limits;
and when each bar in the batch has been rolled, the mill is altered,
refixed, and again the rolling goes on till each bar has passed seven
times at varying pinches through these rollers. Owing to the wear
of the moulds in which the bars are cast—and which is largely due
to the presence of minute portions of antimony in the gold—the bars
are never of uniform thickness; hence bars of every denomination are
passed through the rollers on their edge, so as to reduce them to one
uniform thickness, otherwise the fillets resulting would be ragged,
and of unequal widths, which defect would cause them to produce blanks
out of _remedy_[17] as to weight. The rollers are set face to face;
the graduated scale H is then fixed at zero; if now the rollers are
separated until there be a space of 1·00 inch between them, the scale H
will indicate 50; if, however, it be desired to read a higher figure,
part of another revolution must be performed, causing the scale to
read, say 31·50 of that revolution, when the rollers will be so far
apart that sovereign bars which pass between them will, allowing for
the expansion after compression, be found to be exactly 1·375 inches
wide.
[Footnote 17: See p. 39.]
If now these bars be rolled on their sides, the mill must be turned
down till the scale reads 45, when, if the bars be passed through, they
will measure as under for width and thickness at each successive pinch.
A _spring-pinch_ means the passing the bar once more through the mill
without altering the distance between the rollers.
A sovereign bar passed Becomes a fillet or ribbon—
through the rolling mill— Inches wide. Inches thick.
At 45·00 1·450 0·775
” 35·00 1·540 0·610
” 26·00 1·610 0·460
” 19·00 1·665 0·335
” 14·00 1·696 0·250
” 10·50 1·712 0·194
” 8·50 1·765 0·148
” 7·00 1·778 0·129
” 1st spring-pinch. 1·778 0·127
” 2nd ” ” 1·778 0·120
” 3rd ” ” 1·779 0·118
” 4th ” ” 1·781 0·117
When the bars have passed through the rollers at 10·50 they have become
of great hardness, and of considerable length, say 6 or 8 feet. They
are then taken to the shears K, where their hollow ends are cut off,
and the bars cut into lengths of 18 inches; or rather, such was the
practice when it was considered wise to obtain as much coined money as
was possible from the bars; but recently, under other considerations,
the old plan of the moneyers has been re-introduced, that of shearing
the hollow ends from the bars before rolling. In this process there
is needless waste, and it is to be hoped that the proper practice
will be reverted to, for under that system the ends averaged 4·26 per
cent., while under the re-introduced one it amounts to 7·03[18] per
cent. on the bars, and for the following reason. When the metal is
poured into the moulds, it almost immediately solidifies, and while
solidification is going on contracts in volume, leaving a kind of cup
of metal or hollow part on the top of the bar. In the act of rolling,
the bar maintains an equable width until this hollow part is reached,
when it suddenly expands, and at this point the workman shears off
the defective part of the bar, whereas in the other case he shears
off the hollow end until his eye fails to discover the effects of the
shrinkage; hence the loss of 2·77 per cent. on the produce of fillets,
as well as the loss in wages for melting the bars. The shears may be
regarded as large scissors driven by a drum on the same shaft that
carries the driving wheel for D. The drum is eccentric, so that at each
revolution the shears are caused to open and shut. The bar being placed
between the jaws K, the long end L of the shears is raised by the drum,
and the piece is cut off. The shears may be closed and the end of L
suspended, when out of use, by a hook on the end of the screw worked by
the lever M. The length at which a bar is to be cut off is regulated by
the gauge shown at N.
[Footnote 18: See page 112.]
[Illustration: Fig. 5.—Annealing Furnace.]
The sheared bars are placed in copper tubes, the tops of which are
luted on with clay. It is imperative that the copper tubes should be
made without solder, because this fuses at a temperature below that
which is required to anneal the gold; if present it would run down
upon the hot gold, and cause it to fuse and alloy with the solder,
thus spoiling the work and entailing expense upon the coiner. The
tubes which are used in the Royal Mint are made by Messrs. Benhams
and Froud, of Chandos Street, Strand, who, after considerable pains,
arrived at a method of making the tubes in such a manner as to entirely
satisfy the requirements of the Mint. The tubes A are placed on an
iron carriage B, which is then run into the furnace, as shown in Fig.
5. The door of the furnace C is closed by raising the counterpoise D;
the heat of the furnace is regulated by the damper E. The apron F is
sometimes of use in annealing very long silver bars. After remaining
in this furnace for twenty minutes, the carriage is withdrawn, and
the tubes, taken with tongs, are plunged into cold water, to cool the
gold as rapidly as possible. The rapid cooling of gold and silver
gives to each metal a peculiar character, which is of value in the
after processes, and prevents the access of the atmosphere, which, in
prolonged cooling, would cause the oxidation and consequent removal of
so much copper that the alloyed metal would become too rich in gold
for circulation as coin. The annealing of some metals is effected not
so much by the continued heat as by the slow cooling; it is therefore
wise to raise the metal to its full heat as rapidly as possible, and
then so to arrange matters that it may cool very slowly. This method
does not hold good in the case of the precious metals and of copper,
for they become, under such treatment, so soft, malleable, and pasty
as to stick to the machinery, and thus to cause considerable trouble
and loss. After annealing, the bars, which are now called _fillets_,
go again to the breaking-down mill, through which they are passed with
the scale indicating 8·50, then at 7·00, and after this are submitted
to another pinch without altering the scale at all; so that what is
called a _spring-pinch_ is given, with the intention of effecting the
reduction of the fillet to one uniform thickness, for the breaking
down and subsequent rolling cause the fillets to become much thicker
in their middle than at their sides. The spring-pinches reduce this,
while at the same time they diminish the elasticity of the metal, and
fit it for the other mills. It will be seen, by reference to the above
table, that the widening of the fillet is very trifling; but width may
be gained to any desired extent, at the will of the workman, if the
bars be submitted to a heavy pinch instead of a series of light ones.
The fillet having been submitted to the fourth spring-pinch, is gauged
on its side by a steel instrument, of which Fig. 6 is a representation.
It is a hollow wedge, which is graduated to the thousandth of an inch.
Supposing that the opening from A to B were extended until it were
one inch wide at A, the space would be divided between it and B into
1,000 parts, and then every fillet passed into this opening would stop
at a given point, say, for instance, at 140; such being the case,
every part of the same fillet should be arrested precisely at the same
point. The fillets are reduced till they measure 117 on this gauge,
and are consequently 0·117 inches thick. They are then passed to the
next mill, where they receive four light pinches, and then to a third
mill, where they receive two more very light pinches, and by means of
these six pinches are reduced in thickness to 0·075 inches. They then
pass to another mill, still finer than any of the preceding, and here
are submitted to four very light pinches, by which they are reduced to
0·058 inches, and are finally finished at the sixth or gauging mill,
where they receive three pinches, and are then 0·053 inches thick by
1·829 wide.
[Illustration: Fig. 6.—Small Gauge.]
[Illustration: Fig. 7.—Gauging Mill.]
[Illustration: Fig. 8.—Ansell’s Standard Gauge.]
The gauging mill is of different construction from the other mills, as
may be seen by reference to Fig. 7, where the rollers A are seen in the
act of reducing a fillet. The upper roller is fixed in brasses loosely
clamped together; the upper brass, B, being firmly bolted to the main
frame of the mill by the screws _c_, while the lower one C, which
carries the weight of the roller when it is running empty, is supported
by spiral springs shown at D. The lower roller works on a brass, E,
which rests on a wedge shown at F; the brass being cut to fit the
wedge, so that it may become similar to a solid mass, irrespective of
any motion given to the wedge. By this mode of adjusting, a difference
of the 0·001 of an inch may be made with ease between the distance
of the rollers, and, consequently, in the thickness of fillets which
may pass between them. The wedge F is moved forward and backward by
the screw G, which itself has motion from the gear work H, by the
handle I. Directly a fillet is passed between the rollers, the topmost
one is forced against its upper brasses, and further upward motion
becomes impossible. The weight of metal in this roller gives rise to
irregularities in the thickness of the fillets which pass from this
mill, causing much trouble and some expense; therefore it is proposed
to support the upper roller by a similar arrangement to that which
affects the lower roller, and to keep it rigidly against the upper
brass, but with just so much pressure as its own weight would induce
were circumstances reversed, and by these means to relieve the fillet
from the weight of the roller, because that has an undue influence on
each end of it. The gauger of fillets requires other tests besides that
of the thickness of the edge of the fillet, so he punches out a blank
from an occasional fillet by a hand-press, the cutter of which is shown
at J, Fig. 7, worked by the handle K, through the screw L. The blank
falling through the bolster of the cutter is caught at M, and is then
weighed in the hand scales N, against a standard weight, from which it
must not vary more than 0·50 grain. O, Fig. 7, is the gauge actually
used by the workman; Fig. 6 represents the standard gauge used only
by the officer in charge to check the work at its various stages. He
has in addition a gauge of great accuracy, by which to measure the
fillets at any point, as to width and thickness. This gauge will be
more intelligible by reference to Fig. 8. A is the handle, which is
hollow; B is a lever attached to the flat rod of copper C, which at D
is cut with a rack, into which a pinion E is made to work. The pinion
E works on a shaft, the upper end of which carries a hand F, provided
with a vernier G. If now the handle A be firmly held by the hand,
while the thumb be made to press the lever B towards the end of the
handle, the rod C is set in motion, and causes the hand G to travel in
the direction of H. The rod C rests on another rod I, made of steel,
and so long as to pass into the handle of the instrument. The ends of
the rods C and I are fitted at _b_ with steel shoulders, and are then
continued, as represented, to _a_. If it be desired to measure the
thickness of a fillet, the points _a a_ and _b b_ are caused to open by
pressure applied to B, and the fillet is placed between the points _a_,
when a spring fixed in the box K brings back the rod C as soon as B is
gently released, and encloses the fillet. The separation of the points
_a_ by the fillet causes the hand or indicator G to stand at a point
from zero, which is then read. The scale is divided into 500 parts;
and if the points be opened 0·50 inch, the hand makes one revolution;
so that the ·001 of an inch is gained by one reading. But each 0·001
is subdivided by the vernier into ten, so that a ten-thousandth part
of an inch is read without trouble. To measure the diameter of a blank
coin, or the width of a fillet, it must be placed between the points
_b_; but since the extreme graduation of this gauge is 0·50 inch,
it is necessary, if it be desired to measure a larger diameter, to
press back the lever B till the zero of the vernier G reaches 0·500
on the scale H, and hold it there while a clamp is made fast at the
spot indicated by the star (*), to prevent the motion of C without I.
When the clamp is fixed the rod I must be drawn out till the zero of
the vernier reaches that of the scale H, when the screws J must be
tightened to retain I in its new position, with half an inch permanent
opening between the points _b_ and between the points _a_. In a new
measurement, that permanent 0·500 must be added to the reading. This
arrangement admits of measuring up to 3·5000 inches, to which limit the
gauge is extremely accurate. The instrument was invented by myself,
because I found it difficult to convince the men that the fillet was
thickest in its middle, and consequently heavier there than it should
be; and, unfortunately, that the workmen habituated themselves to
attributing this fault to each other, when its existence was proved.
The fact was, that under the system which had prevailed, the men—with
a view to make bad work for a specially-designed reason—would set the
upper rollers at varying angles, so that a fillet at one mill would
have one thin and one thick edge; and when that fillet passed through
the next mill, the angle of the roller being altered, would make both
edges alike, but the effect of the manœuvre was to push the metal into
the middle of the fillet, and thus to unfit it for the draw-bench.
Hence the necessity to fix where the blame should rest, and the
production of this instrument, under my direction, by Mr. C. Becker, of
30, Strand, at once overcame all those difficulties.
[Illustration: Fig. 9.—Small Shears.]
[Illustration: Fig. 10.—Flatting Mill.]
The fillets are weighed from the rolling room to the drag room, where
they are finally adjusted; for with every energy, discretion, and
skill, FILLETS CANNOT BE OBTAINED OF UNIFORM THICKNESS BY SIMPLE
ROLLING. In the drag room the fillets are taken to the small shears,
Fig. 9, by which one end of each fillet is trimmed so as to render it
square. The plates A are fixed to the head of a T-shaped lever, which
is caused to oscillate by a cam beneath the floor. The plates A shut
against a face of steel fixed to a block, and held by the screws shown
at B; if therefore the end of the fillet be passed between the plate A
and the face of B, each oscillation causes the cutting off of so much
as protrudes, the pieces cut off falling into the box C, which has now
been enlarged so far as to form a pan all round the top with a view
to catch all of them. D forms part of a chain, by which the shears
are thrown out of motion. The fillets, having been trimmed so as to
render their ends square, are next passed to the extent of about two
inches between the rollers of a flatting mill, shown in Fig. 10, which
reduce that part of the fillet to about two-thirds its thickness. A
A represent a pair of small rollers, the upper one of which is cut
with three flat faces, so that it has three rounding and three flat
surfaces; hence, when both rollers are revolving, there are spaces with
openings between them; but when the rounding faces come down, those
openings are much narrowed, so that any fillet placed between them
becomes thinned to just such an extent as may be deemed necessary. The
rollers travel in opposite directions, so as to cause the expulsion
of a fillet placed between them. The reverse motion is gained as
follows:—The upper roller is driven by B, which receives its motion
from the little pinion C, carried on the shaft which also supports D.
D reverses the motion of E, which is driven from the drum F. E also
drives G, which gives motion to the lower roller. The fly-wheel H
is borne at the extreme end of the shaft which carries F and E. The
fillets are rested on J while being _flatted_, and are, after flatting,
placed in the trough K, from which they are taken to a rolling mill in
the drag room, of precisely the same construction as that exhibited at
Fig. 7, to be passed twice through at equal pinches, with a view to
render them still more accurate than they were when leaving the rolling
room, as well as to reduce them to the exact thickness at which the
trier has found they will produce the best work at the draw-bench. The
rolling mill in the drag room was provided with steel rollers. Steel
rollers are of somewhat recent invention, and seem to have received
a high character from those whose opinion may be modified by further
experiments more accurately made. My opinion, founded on experience,
is to the effect that they are not worth their extra cost; but that
their usefulness may be more fully developed when they shall have been
fitted with the arrangements proposed for the gauging mills before
explained.[19] After these alterations have been made, it may fairly
be questioned whether steel rollers will, under circumstances every
way similar, produce better work than is produced by the ordinary
chilled-iron rollers; in other words, I believe that steel is not a
better substance for rollers than chilled cast-iron. Those who have to
sell, and those who have to use, have, of course, different motives;
he who has to use a machine should judge calmly, and not be led away
because the invention is new. It is amongst these considerations that
I am convinced that steel rollers do not save money; for if they wear
longer without getting out of order, they also require a longer time
to put them again in order. Rollers, made from whatsoever substance,
cannot reasonably be expected to produce a fillet from every part of
which blanks of equal weight can be struck, because it is not yet
possible to produce a compound of equal hardness throughout; but if the
construction of the mill be altered, steel rollers may approach nearer
to that perfection which is gained by the draw-bench, but they can
never replace it. The fillets are taken from the mill to the draw-bench.
[Footnote 19: See page 23.]
[Illustration: Fig. 11.—Draw-bench.]
[Illustration: Fig. 12.—Head of Draw-bench.]
Fig. 11 represents the _draw-bench_, the name of which is retained,
as being in fact its only appropriate one. The _flatted_ end of each
fillet is passed into the opening shown at A. The _dog_ A´ is then
run up till its teeth seize the fillet. The lever is depressed until
one of the hooks O catches a bar of the circulating chain P, which
in its onward motion drags the dog, and causes it to bite the fillet
and _draw_ it through the opening at which it has been entered. P
gets its motion from a notched cam, the axle of which is shown at Q.
There are two distinct chains to each draw-bench, and there are two
distinct draw-benches, so that one description does for both double
ones. R is a cogged wheel, the shaft of which, Q, carries two notched
drums, and each drum gives motion to a chain, so that both chains
travel at the same pace. R is set in motion by the pinion S, on the
shaft which is driven by the wheel T. T is driven by U, which is on
the shaft driven by the strap and drums V. Fig. 12 is a representation
of the head of the draw-bench, and in studying this engraving it will
be well to refer at the same time to Fig. 11. The dog takes its name
from its resemblance to the head of a bull-dog. It consists of a pair
of levers, whose long arms extend beyond the axle-tree of the wheels
nearest to O, and whose shortest arms are formed by the passing of the
other axle-tree through the lever. The teeth are set at the front of
the short arms. The axle-tree near O is fixed to the bars forming O,
and runs loosely between the long arms of the lever, so that when O is
pulled forcibly it causes the axle-tree to open the long end of the
levers, and thereby to close the short end or teeth of the dog, the
more rigidly in proportion to the pressure exerted at O. Directly the
fillet has passed through the cylinders the dog springs slightly by the
elasticity of the fillet, and thus releases itself from the chain; at
the instant of release the weight over the foremost wheels falls, and
by its fall lifts the hooks O so high as to admit of their escaping
contact with the circulating chain P. The position of the teeth of
the dog is shown by A in Fig. 12. The flatted part of the fillet is
just so thin as to admit of its passing easily between the cylinders
B until seized by A, but the part which is not thinned comes against
the cylinders B, and requires considerable force to drag it between
them. The cylinders B do not rotate; in fact, they may be considered as
forming part of a solid mass.[20] The lower cylinder is laid on the bed
C, and is clamped there by a cheek fastened on to C by three screws,
the holes for which are shown on C; the upper cylinder is fixed to
the mass D by a precisely similar arrangement. The beds C D are held
perpendicularly by the points of the screws E; and we may now view the
cylinders as secured to, and forming part of, their beds. The distance
between the cylinders is regulated by the capstans F, which separate
the beds of the cylinders, and so separate the cylinders. The accuracy
of this adjustment is all-important, because the distance between the
cylinders determines the thickness of the fillet which passes between
them. The bed D of the upper cylinder is required to be movable at
pleasure; it is therefore provided at G with four wedges, two of which,
_c c_, are cut so that if looked upon from the top a round hole shows
itself, and through this hole the end of the screw, which at this
point L is plain, and has a neck turned in it, passes, with its head
beneath the wedges and against the lower G. So soon as this is effected
the wedges A B are pressed into their places, and these holding _c c_
together, cause them to secure G by its neck; if, therefore, G be now
caused to rise, the block D must rise with it, but the head of this
screw rests on the solid block D, while its neck is just so long as
to admit of this without itself being pressed against the wedges _c
c_. G is a very fine-cut screw which fits into a female screw cut in
the frame of the head of the draw-bench; it is moved to any distance
varying from the hundred-thousandth part of an inch (0·00001) and
upwards by the wheel H, which receives a very minute motion from the
pinion I by means of a lever fitting into the capstan head J. K was
originally intended to be used to set or fix the screw G when it had
been brought to its proper position, but it is not used; for, in fact,
the cylinders wear away appreciably by the passage of the fillets, so
that they constantly require to be brought nearer together to make up
for this wear. With some species of gold the friction is so great that,
although oil is used, the cylinders become so hot as to render the
gold pasty; in such case a kind of welding takes place, which causes
the tearing of the fillet. If this extreme point be not reached, as
indeed it seldom is, the cylinders become of varying temperatures,
and so great is the effect of this, that in order to compensate for
it, the upper cylinder has to be continually raised or depressed. The
beds which carry the cylinders become worn by the strain and fret,
and require grinding out at intervals; therefore, to allow for the
difference which this would make, screws N are provided, by which the
cylinder in the lower bed can always be raised to its proper position.
We cannot but admire the ingenious productions of inventive minds;
and surely if ever there were a marvellous machine for assisting the
coiner, it is this; indeed, it may be doubted whether a more admirable
instrument for its purpose can be contrived. Sir John Barton, who
invented and directed the making of it, took into consideration every
circumstance which could possibly arise, but he never saw practically
the full advantage of his conception. Under my direction, this machine
was so used that the average work produced was very favourably compared
with the trials recorded by Sir John Barton, and details of which were
given to me by the late Mr. W. H. Barton. There are some persons who
smile at the draw-bench, but it is one of those inventions which will
outlive its detractors, at least, so long as economy and perfection
are points to be studied in coining. Foreign Mints are said to have
found no advantage in the use of the draw-bench. It is to be regretted
that they have not found a man with sufficient intelligence to use
so accurate an instrument; it is surely not the fault of the sun if
men are blind to its splendour. Mr. J. Martin, of the Paris Mint, has
recently made some very accurate experiments with the draw-bench,
and has produced results every way in accordance with those obtained
by me in the Royal Mint, and is convinced that the draw-bench may be
considered as the coiner’s right hand.
[Footnote 20: As the cylinder wears, the screws of C may be loosened
to permit the shifting of the abraded part, so that the whole
circumference of the cylinder may be used.—See also page 31.]
Against all sound advice the Master had been induced to buy a pair of
steel rollers, at a cost of £800 (I state the sum on the authority of
Mr. W. H. Barton, who, being Comptroller at the time, probably knew the
actual cost), and with these I made an elaborate series of experiments,
extending over many weeks. The results were wholly adverse to the
new rollers—others arrived at the same conclusion—and I reported to
the Master, in writing, on the facts as I found them, showing that
the average gave an advantage of 19·92 per cent. in favour of the
draw-bench, and on this ground I maintained the superiority of that
machine. He replied by a peremptory order, directing me “to prohibit
now and for ever” the “use of the draw-bench, and to take measures for
its removal from the Mint.” Thus absolved from responsibility, I—after
making a written protest—obeyed that which I could no longer withstand.
The result was that the rejected blanks, which had averaged 3·60 per
cent., now advanced to 23·52 per cent. I was unable to avoid this great
expense, and when I spoke to him about it he was not very amiably
disposed; however, he finally wrote me the following note, on which I
remarked to him “that steel rollers, whether driven by cogged wheels or
by straps, would still be steel rollers.”
“_7th June, 1861._
“DEAR SIR,
“In the cutting and adjusting room you may return to the use of
the draw-bench till the gearing of the steel rollers is altered.
I had overlooked the circumstance that in the United States Mint
cogged wheels are not used for that purpose.
“Yours truly,
“THO. GRAHAM.
“G. F. Ansell, Esquire.”
It is satisfactory to me to find that Mr. Fremantle confirms the
opinion at which I had arrived. He says (“European Mints,” page
9):—“The adjustment of the fillets after rolling is in some European
Mints performed by the draw-bench, as in England. In others it is
performed by carefully adjusted rolling mills only. The experience
acquired both in this country and abroad tends to show that it is
advisable to retain the draw-bench—at any rate, until some more
accurate method is found of equalising the fillets and reducing them
to their correct thickness.” If Mr. Fremantle will investigate for
himself instead of being guided by the opinions of others, he will
rigidly follow the correct conclusion at which he has arrived; if,
however, he will look in the drag room in the Royal Mint, he will
discover evidence of the former existence of a series of rollers which
were replaced by the draw-bench. Yet one of his co-travellers, who is
manifestly willing to make experiments, says of the draw-bench, “Still
it has yet to be proved that it can compete in sustained accuracy
with a well-constructed rolling mill.” Quite true; but I think the
answer holds good, and any one who would replace the draw-bench by
rolling mills—which have hitherto failed—should, as Sir John Barton
did, prove his proposition otherwise than at the Government expense,
and then on success obtain fair remuneration. Before leaving the study
of this instrument it is right that I should mention that Mr. John
Murray, of the Royal Mint, has added immeasurably to the value of
it by inventing a most ingenious machine for grinding the cylinders
(see B, page 28) with accuracy, so that those cylinders which have
been used can with ease be, as it were, repaired. In justice to Mr.
Murray I should add that I omitted all mention of his invention in any
former issue, because some principal contractors were to my knowledge
intending to make him an offer of a sum of money for it, and under such
circumstances I could not think it right to give a description of it. A
like feeling induces me to postpone to another occasion details of this
clever contrivance; its simplicity is such that a mere outline would
put a maker of instruments in possession of means for its construction.
The fillets which have passed between the draw-bench cylinders are cut
into lengths of about 18 inches by the shears shown at X, in Fig. 11,
and are then sent to the trier, who by means of a hand-press similar
to, but more delicate than, that shown at Fig. 7, punches out one or
two blanks from each length of 18 inches, and weighs it, or them,
against a standard weight, and in accordance with his judgment directs
the fillets to be cut by the boys or men at the machines. The trier
allows 0·20 grain on the pound of blanks for the loss which afterwards
occurs by annealing.[21] If, however, the bars, as previously
suggested, were cast uniformly of the thickness of 0·50 inch, this
allowance, which is equal to a value of £34 8_s._ 7½_d._ on each
million, need not be made; but in fact, as will be seen, even this is
not sufficient to cover that loss under present circumstances.
[Footnote 21: See page 48.]
Not only has it become a habit to smile at the draw-bench, but every
unfair attempt has been made to get rid of it. Officers were abused
because they would not report against it, and the machine itself was
submitted to usage never contemplated by the inventor. The then chief
coiner, who had formerly seen soap used in calico works in Manchester,
insisted on using soap-suds, whereby the beds for the cylinders became
rusted, the cylinders destroyed, and the whole machine thrown out
of gear, so that 30 per cent. of all the work was rejected: these
perverse trials, extending over weeks, appeared to throw discredit on
the draw-bench. Having been a calico-printer, that officer endeavoured
to engraft on to the processes of coining some of the practices
adopted in that business; but had he duly appreciated the principle
on which the draw-bench acts, he could not have attempted the use of
soap-suds, or, at least, on its complete failure would have assented
to its disuse. The very first object of the draw-bench is to produce
just so much friction as will cause the lateral displacement of the
molecules of the metal then under its operation. Soap, when it adheres
to the bullion, permits the fillet to pass without friction, and
when it is scraped off by the cylinders the gold becomes so hot from
friction that the hand cannot with safety touch it; hence there are
alternating parts of the fillet very hot and absolutely cold, and, as
a consequence, no two blanks can be obtained of equal weight. Sir John
Barton not only made the machine, but determined also that oil was
the only fit lubricator for metal made to pass through the cylinders
of the draw-bench. Forgetful of the immediate wear on the surface of
the metal, others have attempted to replace the cylinders by wedges of
steel, so made as that a constant stream of cold water should keep them
cool when in operation. This also failed from the formation of rust,
while the work produced never equalled that obtained from cylinders.
The proper use of the draw-bench is to reduce fillets to an equable
thickness in every part, and this can only be done when the trier,
after studying the quality of his metal, has determined how much he
can remove by once passing through the cylinders; then by keeping up
a constant succession of fillets, properly smeared with oil, so that
the equable friction always maintains them at the same temperature.
Under such circumstances, and with a remedy of 0·24 grain, the rejected
should not exceed 2 per cent., and this on the whole day’s work should
contain half its weight of light and the other half heavy blanks. This
also was a curious instance of want of knowledge on the part of that
controlling officer, who for years maintained that if the work were
properly conducted _all the rejected_ should be on one side of the
remedy.[22] The fillets, notwithstanding the draw-bench, cannot be
brought to perfect accuracy, and to meet such variations as arise, a
difference is made in two of the cutting-out punches by altering their
diameters to such an extent that a blank cut by them from a standard
fillet would vary in weight from a blank cut by a standard cutter from
the same fillet. One cutting-out punch is so altered that a blank
would be 0·125 grain, and the other that a blank would be 0·250 grain
heavier. This admits of a fillet otherwise too thin being used; but if
the fillet be found to err on the other side, it is passed once more
either through the draw-bench, or through the mill at a spring-pinch.
The trier, Mr. William Fenton, is a peculiarly steady man, possessing
a calm judgment, with considerable energy, and upon him depends the
accuracy of the whole process of coining; he has not unfrequently so
managed his work that upon 5,000,000 of sovereigns coined, he has been
within one sovereign of the calculated value.
[Footnote 22: See page 39.]
The fillets, having been thrown by the trier into the receptacles which
indicate the particular cutting-out punches to which they are to be
taken, are fetched by a man, who wipes off the oil, and then carries
them to the cutting-out room, where the fillets are cut into blanks
and scissel. In this place it may farther be noticed that soap-suds
cannot be used in the place of oil, because the soap could not be
removed without washing,—a practical impossibility,—and would therefore
remain, and add indefinitely to the weight of the gold, and thus open
the door for peculation. The cutting-out presses used in the Royal Mint
are very cumbersome, and when in operation are terribly noisy: it is
therefore hoped that at no distant period they may be replaced by some
of a far more simple construction; but it is believed that under all
circumstances it will be found wise to adhere to the plan of cutting
out a single blank at each descent of the punch.[23] For bronze it
is well to obtain five or more blanks at each blow, but the limited
variation of weight allowed by law on blanks of the precious metals
would render this false economy. Fig. 13 represents one of the twelve
cutting-out presses, which are all driven by the wheel A, provided
with a series of cams on its outer rim; one of these cams, B, is in
the act of striking the friction roller C, which is attached to, and
forms part of, the lever D. D is fixed to an upright shaft E, which
at F is cut with a screw thread working into a female screw fitted
into the main shoulder of the press at G. If now the cam B strikes
C, and throws it outwards, it causes the shaft E to take a part of a
revolution, and in so doing the screw F makes it rise and carry with
it the block H, whose tendency to circular motion is prevented by a
plug fitting into its groove, and fixed in the guide I. The lower end
of H carries the screwed cap J, which supports the cutting-out punch,
so that when E rises it carries the cutting-out punch through just the
same distance that itself travels upwards. The cutting-out punch is
now ready for action, and is released by the continued revolution of
the wheel A, as will be seen by the figure; but as it could not fall
with sufficient force of itself, assistance is rendered by the pressure
of the atmosphere, as will be seen by the following arrangement. The
lever D is provided, near its junction at E, with a loop of iron
travelling on a screw, so that it may be moved farther from, or nearer
to, the centre of action, and thus admit of the increase of power.
This loop of iron is represented by K, and is continued by a rod of
iron across the upper part of the room and through a hole in the wall
to a system of levers L, from which a rod is suspended, the lower end
being connected with a piston working in the chamber M. The chamber M
is an hermetically-closed vessel secured to a stone firmly fixed in the
floor. The piston works in this chamber, and is covered with about two
inches of oil, which prevents the access of the atmosphere by leaks to
any part beneath the piston. If the piston, therefore, be raised from
the base of the chamber, a vacuum is produced in that portion from
which the piston is removed, and consequently the atmosphere presses
on the surface of the oil, which in its turn presses on the piston,
and carries it down (the reverse of the action explained by Mr. James
Napier in “European Mints”); in its fall the piston pulls down the
cutter, which has been raised; for the same blow which raises the
cutter also raises this piston; therefore, when the cutter is raised
the workman places the fillet N, from which blanks are to be cut, on
the bolster, shown at O, and holds it firmly while the cutter descends
and punches out a blank, which falls through the bolster into the
drawer P. By the time that the down stroke of the cutting-out punch is
complete, the wedge Q has entered a slit in the spring R, and strikes
the spring, thus throwing the machine back, and preparing it to start
when the cam B shall strike the friction roller C. The point at which
Q may strike R is determined by a screw near the left-hand T. The
upright shaft E, which is partly hollow, terminates at a flat cogged
wheel, and the upper part of F is made to pass into E; while at S is
an arrangement which serves to detach or connect these pieces, that
the cutter may upon occasion be used by the hand by means of the lever
T, as well as to admit of the necessary alterations, as the punches,
by regrinding, become shorter. The cutting-out punch, when it rises,
carries with it the fillet from which the blank has been punched, until
the fillet comes against the guard W, which detaches it.
[Footnote 23: See p. 169.]
[Illustration: Fig. 13.—Cutting-out Press.]
The fillets from which the blanks have been punched have the appearance
of ribbons perforated with round holes, and are now called _scissel_
(from the Latin _scindo_, to cut). These are thrown into a tray, U,
from which they are taken at intervals, and bound up by strips of the
same into bundles of 180 ounces—in the case of silver 360 ounces—ready
for re-melting. The cutting-out press is set at liberty to start by
the workman pressing his foot on a lever in connection with the line
and spring indicated by V; and so long as he keeps this lever down,
the press is worked continuously, but when he releases it the spring
catches the extreme end of D, and motion is arrested. The blanks
which accumulate in the box P are collected at frequent intervals and
examined, to see that their edges are smooth; if they be ragged, as
may happen from the wear or fracture of the edge of either the cutter
or bolster, a loss would be entailed in after processes which would
cause the coin to be outside the prescribed limit, and to pass at an
illegal weight into circulation, as the rough edges would be removed
after the weighing of the blanks had been effected. According to
the quality of the work—the character of the gold—under operation,
the trier tests more or less frequently the variations of weight in
a given number of blanks. This process is called POUNDING, and is,
next to the _trying_, the most important of his duties; if such an
expression can be admitted, he has, by _trying_, fired his shot, and
here determines if he has hit the bull’s-eye, all depending on his
own unaided judgment. The gauge, Fig. 8, is found of great service in
detecting irregularities as to diameter and thickness, which would not
be, and are not, detected by weight, for the weight may remain equal,
although both diameter and thickness may vary. All these points require
considerable care on the part of those whose duty it is to attend to
them; for the quality of a coinage is determined in this room: blanks
which once leave it cannot be afterwards altered. The subsequent
operations, being purely mechanical, would be quite as well performed
by automaton machines.
The completing processes form undoubtedly the prettiest and most
interesting part of the operation of coining; nevertheless the
processes already described constitute its most essential features.
The blanks are weighed from this room in drafts of about 720 ounces,
and placed in bags; each bag, therefore, contains four _journeys_ of
about 180 ounces each. The term _journey_ is said to be derived from
an old French word, but circumstances render it probable that this
derivation has been applied by others than the original inventor of
the word, for it manifestly was not used by the coiner of it to imply
a “day’s work.” I cannot find an author who gives a time at which 720
ounces of silver became a journey, while 180 ounces of gold were also
called by the same name. It must have taken far longer to coin 720
ounces of shillings or groats than to coin 180 ounces of sovereigns or
half-sovereigns; hence the same word could never have been intended to
mean “a day’s work.” Be this as it may, it is time that such names gave
place to more appropriate and expressive terms. It is to be hoped that
500 ounces will become the standard maximum weight for bags of either
of the precious metals; such a system would be the means of reducing
the chance of error, it would have an actual meaning, and would be a
convenient weight for a man to lift to and from a scale-pan. When such
a measure shall be convenient to the officers of the Bank of England,
that institution will subserve the interests of the Mint by adopting it.
In a paper recently published by the Commissioners on the International
Coinage (at page 228) it is stated that “in the British Mint 15 pounds
troy of standard gold are coined into 701 sovereigns nearly (15 lbs. =
£700 17_s._ 6_d._).” This statement does not exactly convey the truth,
and is calculated to mislead, because such an operation is not, and
never has been, conducted in the British Mint, where the invariable
rule is to abide rigidly by the law, and to coin 20 pounds troy weight
of standard gold into 934·50 sovereigns, as specified in the Mint
Indenture, now replaced by the Act of Parliament, 33 Vict., cap. 10.
Of these sovereigns so coined, 701 are placed in a bag, and called a
_journey_; but by a Mint fiction the journey was considered by the
old moneyers, and yet more ancient weigher and teller, 15 pounds troy
exact, because the parts of an ounce were difficult of addition; and
this was maintained until 1860, when a disputed weight with the Bank of
England as to the value of the deliveries corrected that which I had
previously pointed out as an error. It is now the custom to consider
a journey as consisting of 180·03125 ounces, instead of, as it is,
180·03210 ounces, an error of ·00085, which has a money value of about
6_s._ 7½_d._ on each delivery to the Bank.
[Illustration: COTTON’S PATENT AUTOMATON BALANCE.