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Presses and Pressroom Practice.  The machines in which coins and medals are struck and their operation. Presswork and presses replaced hammer coinage with coins created manually one blow at a time. Presses have evolved from manual hammer and screw presses to mechanical machines that spew out tens of thousands of pieces struck an hour in modern times. Factors of impression, speed, control and maintaining sustained quality have been important in press design and construction over the years. The pressroom – usually with presses of several makers or types – is where coins and medals come to life by die stamping under the watchful eye of a skilled pressman, the press operators and their foremen. As the need for coins increase, national mints have banks of coining presses, long rows of presses capable of spouting out large quantities of struck pieces.

Basic considerations.  Presswork – striking and coining – all imply the manufacture of metal pieces by stamping with a press, the controlled force of form and image pressed into metal with dies. This process is cold coining, where the blanks are struck at room temperature (to transfer the design in the sharpest detail possible). Cold coining is in contrast to heating the blanks, called forging, (see drop forge). Striking a flat blank, as for coins and medals, is the meaning of coining (in metalworking); when more evolved work is performed, as bending or drawing, it is called pressing (outside the scope of this encyclopedia).

       Outline of Entry                   

    I. Definition & Overview.             

   II. Basic considerations.              

  III. Historical Development             

       A. Hammer presses.                 

       B. Screw presses.                   

       C. Roller presses.                 

   IV. Coining presses.                   

       A. Knuckle-joint presses.          

          1. Uhlhorn's lever press.       

          2. Thonnlier's improvements.    

          3.  Peale’s rebuilt press.

       B. Modern Coining presses.         

    V. Medal presses.                     

       A. Screw press.                    

       B. Knuckle-joint.                  

       C. Hydraulic                       

   VI. Power, from man to electricity.    

                 Historical Development of Striking Presses

For the first 2300 years of coinmaking, there were no presses. Coins were made one at a time by hammering. A blank of metal was placed between dies and a sledge was applied to the top die. Production was slow, and required the strength of a sturdy man who could wield a heavy sledge. With another workman willing to hold the two dies in place, remove struck pieces and replace with a fresh blank, the production was increased. 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.

Hammer press.  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 Lenardo da Vinci (1500) had when he theorized how sheet metal could be blanked, and the blank be struck. His concept was brilliant, he had the same press doing both operations back-to- back, where the operator would do first one, then the other. We have no record that a Da Vinci press was ever built, but a press for striking only, similar to Da Vinci's concept, was used in Saint Petersburg, Russia, at an unknown time (probably long after more advanced presses were in use in Europe).

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 press.  The screw press for striking coins was "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). Renaissance artist Benvenuto Cellini used 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 and draw plates for preparing metal for blanking. The 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.

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 (and a better rim). 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 it wasn't until 1641 when coins were struck 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). His concept was unaccepted until Edinburg where he 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.

Development of Coining Presses

What the Industrial Revolution 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. A German, with great mechanical insight, best solved this task.

Uhlhorn adapts the knuckle-joint to coining presses.  In 1812 Deitrich Uhlhorn 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 improvements, as was the feeding mechanism. A Frenchman in 1833 in Paris, Thonnelier (first name 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 to an indexing plate. Some presses continue a horizontal feed with vertical die movement; but one 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.

     Peale’s Toggle Joint Press

                Roger W. Budette

When Franklin Peale returned to the Philadelphia Mint from a year-long tour of European mints in May 1835, he had a set of plans for a toggle-joint press with him. These were not copies of Uhlhorn or Thonnelier presses, but were Peale’s inventive spirit applied to the mechanism of the toggle-joint and the problem of efficient mechanized coinage.

Compared to Thonnelier’s or Uhlhorn’s presses, Peale’s version makes more direct application of force and is clearly built on a more robust, compact and simplified application of the same principles. In most respects, Peale seems to have selected the best from European examples, and discarded all unnecessary complexity and ineffective motion. His coin press is simple, direct, somewhat homely in appearance, but entirely effective in operation.

The basic mechanics of the press are from the same family as Peale’s blank cutting and upsetting machines. All used an eccentric to redirect rotational energy to linear force while maintaining simplicity of operation. On a broader scope, all three were components and principles used in locomotives and stationary steam engines, and these connected back to Peale’s early years working with Matthias Baldwin.

Using the mental processes of a practical machinist, Peale’ press design incorporated features that would make it useful to American mints. Peale’s type of toggle-press had fewer moving parts and a smaller number of critical connections than presses used in Europe. It used large, easily cast iron parts; joints, including the all-important toggle-joint, were robust and easily accessible. Several large parts were made from hollow castings rather than solid metal.

The same design was used for multiple sizes of press, and the operation for all was identical. There were no thin parts or fine adjustments; even the mechanism for altering the pressure was nothing more than a wedge with screw thread and locking bolt. All these attributes made Peale’s press a reliable, simple to maintain piece of equipment that could operate in the humidity of New Orleans, the cold of Philadelphia, or the isolation of Dahlonega without need for a master mechanic.

But like all equipment they required regular maintenance and replacement of defective parts. Cleaning and lubrication of key parts was needed several times a day as well as at the beginning of the work day. In later improvements, some high friction parts were equipped with automatic oilers that dripped lubricant onto mechanical joints. Internal parts could only be oiled by stopping the press and removing access plates or other parts. Excessive lubrication could also create problems, especially in planchet feeding and coin ejection mechanisms. Too much oil caused planchets to stick together, or stick to a die, or refuse to feed into the collar.

Peale continued to make improvements in the coining press for several years afterward. Their efficiency and simplicity exceeded coining presses of any other country’s mints. The improved press ran at eighty-four revolutions per minute and could strike 5,000 pieces per hour or 50,000 per ten-hour work day. It required cleaning, oiling and other maintenance several times per day.

Power for coinage presses came from either a steam engine connected to belts and pulleys, or in the late nineteenth century, a steam engine connected to a generator with electricity sent to a motor on each press. However the power was produced, it was applied to the flywheel and not directly to the striking mechanism of a press. Each rotation of the flywheel represented one complete action of the press. The flywheel, which carried all of the press’s kinetic energy, could be connected or disconnected from the press mechanism by moving a lever which engaged a clutch on the press.

There was very little inertia in the press mechanism so it stopped or started the moment the clutch lever was pulled. Speed of the press was controlled by rotation of the flywheel – faster rotation meant more cycles of the press per minute. Mechanically, the toggle press delivered the same force with every actuation of the device, so striking pressure was largely a matter of die area and spacing. Thus, the number of cycles per minute was not directly related to the pressure of each strike. 

Sources:

Roger W. Burdette, “Invention of a Toggle-Joint Coinage Press–1835,” Journal of Numismatic Research, Issue #2, Spring 2013.

Franklin Peale. “Description of the New Coining Presses Lately Introduced into the U.S. Mint, Philadelphia,” Franklin Journal, November 1836.

Medal Presses

The first struck medals were made on screw presses, but the diameter 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. A 1000-ton press (pressure per square inch) could strike a medal up to six inches in diameter.

It was the development of the hydraulic press which 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 of the blow could be increased by making the  balance beam longer, and then by adding lead weights on the end. It was also affected 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 up 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, Thonnelier and Peale 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 in 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.

References:                                                                                                                        

C54  {1966} Gilbert, medal press, #37, p 25, plate 5.

C82  {1988} Cooper, 74-75 (hammer); 77-78 (tilt hammer); 52-60, 132-133 (screw press); 52-53, 127-157, 230-234 (coining presses).

CH76 {1992} Challis.

Pressman.  The operator of any press used to strike coins or medals, as a coining press or any type of medal press. 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), previously the operator of a screw press who fed blanks and ejected struck pieces manually was called a coin setter. U.S. Mints had a die setter and a press operator. The press operator did not setup the press or adjust the dies.

A pressman's greatest responsibilities with automatic presses are: (1) not to break a die, (2) to use the correct blanks for striking the order at hand, (3) to setup the press properly if not by a special die setter craftsman, (4) to insure the feed mechanism is delivering blanks to the press properly and continuously, and (5) to frequently inspect the struck items during a production run.

The pressman and die setter must have a feeling for die clearance and die alignment during setup and that the dies are seated and locked in correctly. He must know the correct gauge of blanked stock. While presses are running he must have a "sixth" sense of knowing his press is functioning properly and 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 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.

See also presses and pressroom practice.

CLASS 06.5

5727-(005)13.1

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON