This is the third of several reports on the basic information, the basic knowledge, of minting coins and medals. These facts are so important they should be embedded in the repertoire of everyone associated with the medallic field and, certainly, everyone within the firms which make these.
BEFORE coin presses, there was man and manpower. Ancient coins were struck by two men, one holding a die on top of a metal blank on top of second die. The second man wielded a hammer, more like a sledge, for he needed to create a maximum amount of power to drive the top die into the blank and force it into all the cavities of the second die.
The dies even had names. The bottom die was called the anvil die and was usually the obverse of the coin. The upper die was called the pile die, usually the reverse. There were no set rules which should be obverse or reverse. But it was easier to reseat a partially struck piece back on the anvil die for a second blow if needed. Obverses usually had higher relief, with a larger cavity than a reverse, thus easier to place back in position.
To lessen the need for such great striking force ancient coin makers experimented with heating and softening the metal blank. But this only caused uneven metal flow outward causing sawtooth edges of spikes and voids. The name for this was hot tears.
For 2300 years coins were made by hammer blows on unheated blanks. Two men striking one coin at a time, one wielding the sledge, the other removing a struck piece and placing a fresh blank in place (and perhaps saying a prayer the sledge man hit the pile die and not his fingers!)
This manual process, known as hammered coinage, proceeded under the management of a moneyer; it was the major method of coinmaking from 640 bc until as late as 1662. A moneyer typically kept one of every16 pieces as his pay, as he enjoyed his monopoly. It is no wonder they rejected the introduction of any mechanical means of coin making.
Instead of a man wielding the sledge, why couldn’t the sledge be lifted by a pulley and dropped down a channel to affect the blow? This was the concept famed artist and inventor Lenardo da Vinci (1500) developed when he theorized how sheet metal could be blanked, and the blank be struck. His concept was brilliant; he visualized the same press doing both operations back-to-back. We have no record that da Vinci’s press was ever built, but he made sketches in his notebooks which have survived.
[In the 1950s IBM underwrote the building of da Vinci’s press from his notebook drawings. This press can now be viewed at the Smithsonian Institution in Washington.]
Primitive hammer presses (called klipwerk) were in operation for over a century in Germany and Sweden prior to 1763 when they were illustrated in a German encyclopedia. In Sweden the concept of the hammer was modified to a tilt hammer press. Powered by men or horses on a circular tread mill, the power was transferred by a capstan, this raised an arm with the hammer on the end; it would then trip and fall for the blow, the die slamming into sheet copper.
The copper plates were heated before this striking, and the plate was moved from a center strike to the four corners where the die struck there as well, all in quick time. This is the well documented method of manufacture of Swedish plate money from 1644 to 1776.
Screw presses for striking coins were “invented” in 1506. An Italian, Donato Bramante (1444-1514) modified an existing press (perhaps a fruit or olive press) that year for striking lead seals for Pope Julius II (1503-13). Other early screw presses where built by Nicolo Grosso and used at the Florence Mint for blanking at approximately the same time. Renaissance artist Benvenuto Cellini employed such a press in 1530, again for Papal seals, but further, he illustrated it in his book on goldsmithing.
The screw press was further developed by Max (or Marx) Schwab in Augsburg, Germany, in 1550, who also improved on the rolling mill to draw plates for preparing metal for blanking. His rolling mill was immediately accepted by goldsmiths in Germany, but Schwab wanted his equipment used for striking coins. He was unsuccessful in selling his equipment to the Venice Mint, where he first offered it, but the French ambassador learned of his improvements and ordered a set of his “engines” for the Paris Mint. These were installed in 1751 and operating early in 1752.
Screw press operation. Forstriking coins, blanks had to be ready in quantity. Three or five men operated a screw press. One was the coin setter, he removed the struck piece and inserted the next blank. Two or four men were spinners, they operated the balance arm, swinging it back and forth. Lead weights were added to the balance arm to give it more strength about 1740.
Straps were attached to the ends of the balance arm enabling two spinners to pull on opposite ends sending the spindle – the stem with large gears – crashing down with great force onto the blank. The die on the end of the spindle, called the pile, forced the blank into the stationary anvil die forming the design on both sides. The coin was struck.
The other two spinners would pull on their straps causing the spindle to rise. With the arm flying back and forth workers gave this press the nickname fly-press. The crew would change after 20 minutes, but they did this for 5 hours at a time, doing other work at the mint for a 10-hour day. The speed of swinging the balance arm was astounding: 20 to 30 times a minute! They had to develop a great rhythm!
While the screw press was a major improvement, it took more than a century to replace entrenched moneyers and hammered coinage. Moneyers fought the innovation despite the fact coins could be struck with a screw press in quicker time creating a far more uniform coin with a better rim by cold coining. The screw press was introduced at the London Mint in 1551, the moneyers revolted, the screw press rejected, and it was not until 1662, 111 years later that it finally was in full use there.
The same thing happened in France. Schwab’s screw press was introduced to strike coins in 1552, but not until 1641 were coins struck in Paris on a production basis. The development of the screw press, delayed for over a century, was then widely accepted at mints around the world. It was first powered by men, and continued so, but some mints adapted it for water power, then for steam power.
Roller press. Development of the roller mill led to the concept of impressing the rolled strip with the designs first, then blanking afterwards. The idea originated in Germany, but it was Nicholas Briot, who tried it first at the Paris Mint (1606-25), then at the London Mint (1633) and finally at the Edinburg Mint (1635-39).
Briot’s concept was unaccepted until Edinburg where he finally accomplished coinage by roller die (taschenwerke). Despite these early attempts in Germany, Scotland and Spain, this form of coining never surpassed the mill and screw, of rolling the metal, cutting out the blanks first, then striking individual coins.
[General Motors undertook an experiment in the 1960s in cooperation with the U.S. Mint. It built a modern version of such a roller press at one of its experimental laboratories in an attempt to revive this concept. But in operation the press creayed such high temperatures in the steel dies it melted the image on the face of the dies.]
Development of Coining Presses. What the Industrial Revolution – and Matthew Boulton, Father of Modern Minting, with his Soho Mint – brought to coinmaking was the concept of how to do better repetitive steps, to improve the mechanization of striking coins. A blank had to be brought to a position where it could be impressed with both obverse and reverse dies, then the struck piece had to be ejected, the concept of cold coining. A German, with great mechanical insight, best solved this task.
In 1812 Deitrich Uhlhorn (1764-1837) of Grevenbroich, Germany, began experimenting with striking. Instead of one die going up and down (as on the screw press) he employed a knuckle-joint to allow one die to retract enough for the piece to be ejected, the next blank inserted, and the continuous action controlled by a flywheel. This was brilliant and it worked.
By 1817 Uhlhorn had perfected this press; he patents it and begins building presses in a factory he establishes. His first sale was to the Berlin Mint, followed by other mints as they learned of his new press. Uhlhorn, and his sons after his death in 1837, were to build more than 200 presses over a span of sixty years.
Knuckle-joint press improvements. With continued use, other improvements were adapted to Uhlhorn’s knuckle-joint press. The layer-on of placing the blank in position was one of these improve- ments, as was the feeding mechanism. A Frenchman in 1833 in Paris, Eugene Thonnelier (dates unknown) was to do more to improve Uhlhorn’s press than anyone. But he did not manufacture presses, he had no factory, he supplied drawings for presses to be built by local constructors.
The automatic feed eliminated exposure to loosing fingers as is present in all hand-fed presses. Prepared blanks were fed by hand into a tube that brought the blanks into position. Later improvements were made by Taylor & Challen which made Uhlhorn-style presses under license. Even in the 20th century, as late as 1961, Horden, Mason & Edwards placed the toggle mechanism beneath the feed table for a final improvement.
Modern coining presses have reduced the size of the flywheel, enclosed the mechanism with a covering (no moving parts exposed) and have changed the feed mechanism to an indexing plate. Some presses continue a horizontal feed with vertical die movement; but one German press has a vertical feed with horizontal die movement.
Modern presses are manufactured by Schuler and Grabener in Germany, by Reinhard & Fernau in Austria, by Heaton, Taylor & Challen, and Horden Mason & Edwards (now a division of America’s Cincinnati Milacron) in England, by Raskin in Belgium, and by Arboga in Sweden.
Medal Presses The first struck medals (Padua in 1390, Venice in 1393) were made on screw presses, but thediameter was limited, only medals smaller than 40mm could be struck with this type press. With the development of knuckle-joint presses the size was increased but limited by the pressure of the press, so larger presses were built. (Centuries later a 1000-ton press – pressure per square inch – could strike a medal up to six inches in diameter.
The development of the hydraulic press in as early as 1852 led to greater versatility in medal striking. The action of a hydraulic press is best described as a squeeze, in contrast to the blow of a knuckle-joint press. Production of both presses must take into consideration work hardening. A knuckle-joint has greater production speeds but requires annealing more often. Hydraulic press production is slower but has greater surface movement. Both presses are in use in modern medal manufacturing.
Powering the press. The source of power has changed in the last two hundred years. Early screw presses were powered only by man. The power was increased by longer balance beam, then by adding lead weights on the end. Power was also increased by more men pushing on the beam, up to four on each end.
Horsepower was used where the horses could walk in a circle deriving the power by a capstan. This was ideal for a trip hammer press, but not effective for a screw press. Then water power was employed, with power transferred by belts. This was ideal for the Uhlhorn and Thonnelier presses because the belts could be connected to the flywheels.
But steam engines, first developed by Boulton & Watt in 1775 and used in their mint as early as 1788, became the major source of mint power for over ninety years for most mints. It wasn’t until 1883 that electricity began replacing steam power, first at the Philadelphia Mint, then elsewhere; belting was eliminated and separate electric motors ran individual coin and medal presses.
Pressroom practice. The operator of any press employed to strike coins or medals, as a coining press or any type of medal pres, is a pressman.
A pressman reports to a pressroom foreman, who is responsible for all activity to produce the coins or medals. Operators of presses have always been called a pressman since 1819 (although Medallic Art Co has at times employed lady “pressmen”).
A pressman’s greatest responsibilities with automatic presses are:
- not to break a die
- to use the correct blanks for striking the order at hand
- to setup the press properly
- to insure the feed mechanism is delivering blanks to the press properly and continuously
- to frequently inspect the struck items during a production run.
The pressman must have a feeling for die clearance and die alignment during setup and that the dies are seated and locked in position correctly. He must know the correct gauge of blanked stock. He must be able to look at the relief and size of a die to determine the correct gauge to use in striking if it is not specified in the work order.
While presses are running the pressman must have a “sixth” sense of knowing his press is functioning properly by the sound it makes (and how fast he can hit the power button when he hears a clink or thud instead of a hum of satisfactory continuous striking).
He should know just about when a die is going to break and retire it before it can jam the press. (While obtaining the maximum use from a die is an admirable goal, it is less important than that of preventing a die from breaking on the press.) Also he must maintain the press or presses under his command in working order.
During inspection, a pressman must know what to look for. He must know the concept of highpoints (that the metal flow is filling every cavity in the dies by surface deformation). He examines these places on the struck piece under magnification on both sides.
He must be conscious of all the points of stress in a die (he must carefully examine the areas between lettering and the rim where stress is the greatest). He must also examine the rim/edge juncture in trying to meet (but not exceed!) this point with the most metal mass of the blanks. He should check the axis on both sides of the piece that they are properly aligned. His goal is to produce perfect struck pieces at all times.
Presses provide the means of producing multiple replicas of the image the artist created in the first place.