The
planchets are then removed to the adjusting room, where they
are adjusted. This work is performed by ladies. After
inspection they are weighed on very accurate scales. If a
planchet is too heavy, but near the weight, it is filed off at
the edges; if too heavy for filing, it is thrown aside with
the light ones, to be re-melted. To adjust coin so accurately
requires great delicacy and skill, as a too free use of the
file would make it too light. Yet by long practice, so
accustomed do the operators become, that they work with
apparent unconcern, scarce glancing at either planchets or
scales, and guided as it were by unerring touch.
The
exceedingly delicate scales were made under the direction of
Mr. Peale, who greatly improved on the old ones in use. So
precise and sensitive are they that the slightest breath of
air affects their accuracy, rendering it necessary to exclude
every draft from the room.
Progress
in Coining
The
methods of coining money have varied with the progress in
mechanic arts, and are but indefinitely traced from the
beginning; the primitive mode, being by the casting of the
piece in sand, the impression being made with a hammer and
punch. In the middle ages the metal was hammered into sheets
of the required thickness, cut with shears into shape, and
then stamped by hand with the design. The mill and screw, by
which greater increase in power, with finer finish was gained,
dates back to the Sixteenth Century. This process, with
various modifications and improvements, continued in use in
the Philadelphia Mint until 1886.
The
first steam coining press was invented by M. Thonnelier. of
France, in 1833, and was first used in the United States Mint
in 1836. It was remodeled and rebuilt in 1858, but in 1874 was
superseded by the one now in operation, the very perfection of
mechanism, in which the vibration and unsteady bearing of the
former press were entirely obviated, and precision attained by
the solid stroke with a saving of over seventy-five per cent
in the wearing and breaking of the dies.
Dies
The
dies for coining are prepared by engravers, especially
employed at the Mint for that purpose. The process of
engraving them consists in cutting the devices and legends in
soft steel, those parts being depressed which, in the coin,
appear in relief. This, having been finished and hardened,
constitutes an "original die," which, being the
result of a tedious and difficult task, is deemed too precious
to be directly employed in striking coins; but it is used for
multiplying dies. It is first used to impress another piece of
soft steel, which then presents the appearance of a coin, and
is called a hub. This hub, being hardened, is used to impress
other pieces of steel in like manner which, being like the
original die, are hardened and used for striking the coins. A
pair of these will, on an average, perform two weeks' work.
Transfer
Lathe
The
transfer lathe, a very complicated piece of machinery, is used
in making dies, for coins and medals. By it, from a large
cast, the design can be transferred and engraved in smaller
size, in perfect proportion to the original.
The Coining and Milling Rooms
This
department, the most interesting to the general visitor,
occupies the larger portion of the first floor on the east
side of the building. The rooms are divided by an iron
railing, which separates the visitors, on either side, from
the machinery, etc. . but allows everything to be seen.
The
planchets, after being adjusted, are received here, and, in
order to protect the surface of the coin, are passed through
the milling-machine. The planchets are fed to this machine
through an upright tube, and, as they descend from the lower
aperture, they are caught, upon the edge of a revolving wheel
and carried about a quarter of a revolution, during which the
edge is compressed and forced up--the space between the wheel
and the rim being a little less than the diameter of the
planchet. This apparatus moves so nimbly that five hundred and
sixty half-dimes can be milled in a minute; but, for large
pieces, the average is about one hundred and twenty. In this
room are the milling machines, and the massive, but delicate,
coining presses; ten in number. Each of these is capable of
coining from eighty to one hundred pieces a minute. Only the
largest are used in making coins of large denominations.
The
arch is a solid piece of cast iron, weighing several tons, and
unites with its beauty great strength. The table is also of
iron, brightly polished and very heavy. In the interior of the
arch is a nearly round plate of brass, called a triangle. It
is fastened to a lever above by two steel bands, termed
stirrups, one of which can be seen to the right of the arch.
The stout arm above it, looking so dark in the picture, is
also connected with the triangle by a ball-and-socket joint,
and it is this arm which forces down the triangle. The arm is
connected with the end of the lever above by a joint somewhat
like that of the knee. One end of the lever can be seen
reaching behind the arch to a crank near the large fly-wheel.
When the triangle is raised, the arm and near end of the lever
extends outward. When the crank lifts the further end of the
lever it draws in the knee and forces down the arm until it is
perfectly straight. By that time the crank has revolved and is
lowering the lever, which forces out the knee again and raises
the arm. As the triangle is fastened to the arm it has to
follow all its movements.
Under
the triangle, buried in the lower part of the arch, is a steel
cup, or, technically, a "die stake." Into this is
fastened the reverse die. The die stake is arranged to rise
one-eighth of an inch; when down it rests firmly on the solid
foundation of the arch. Over the die stake is a steel collar
or plate, in which is a hole large enough to allow a planchet
to drop upon the die. In the triangle above, the obverse die
is fastened, which moves with the triangle; when the knee is
straightened the die fits into the collar and presses down
upon the reverse die.
Just
in front of the triangle will be seen an upright tube made of
brass, and of the size to hold the planchets to be coined.
These are placed in this tube. As they reach the bottom they
are seized singly by a pair of steel feeders, in motion as
similar to that of the finger and thumb as is possible in
machinery, and carried over the collar and deposited between
the dies, and, while the fingers are expanding and returning
for another planchet, the dies close on the one within the
collar, and by a rotary motion are made to impress it silently
but powerfully. The fingers, as they again close upon a
planchet at the mouth of the tube, also seize the coin, and,
while conveying a second planchet on to the die, carry the
coin off, dropping it into a box provided for that purpose,
and the operation is continued ad infinitum. These presses are
attended by ladies, and do their work in a perfect manner. The
engine that drives the machinery is of one hundred and sixty
horse-power.
After
being stamped the coins are taken to the Coiner's room, and
placed on a long table--the double eagles in piles of ten
each. It will be remembered that, in the Adjusting Room, a
difference of one-half a grain was made in the weight of some
of the double eagles. The light and heavy ones are kept
separate in coining, and when delivered to the treasurer, they
are mixed together in such proportions as to give him full
weight in every delivery. By law the deviation from the
standard weight, in delivering to him, must not exceed three
pennyweights in one thousand double eagles. The gold coins--as
small as quarter eagles being counted and weighed to verify
the count--are put up in bags of $5,000 each. The three-dollar
pieces are put up in bags of $3,000, and one-dollar pieces in
$1,000 bags. The silver pieces, and sometimes small gold, are
counted on a very ingenious contrivance called a
"counting-board."