NNP

Screw Press.  A striking press whose force is derived from a spindle with steep-pitched threads; an early press that remained in use for nearly four centuries before being replaced by modern presses. The first screw presses derived their power from men, working in teams – pushing on opposite ends of a long balance beam and walking around the press – later by horses or by water power; thus their capability was limited to striking coins and medals of limited diameter (certainly less than 40 millimeters, but more often less than 25mm). Not only was the screw press used for striking, see illustration by Benvenuto Cellini who used one in 1530, but was also used for hubbing and adapted for blanking.

Prior to the screw press, coins were made with a blow from a sledge to a punch (containing one design) on a blank laid on a die in the lower position called the pile (containing the opposite design). This coinage is known collectively as hammered and produced by a moneyer. With the development of the screw press, coins and medals truly became struck (see striking).

The process of striking in a screw press was called mill and screw, or simply, milled or mill coinage. The development of the rolling mill not only gave this coinage their name but also gave coins more uniformity in their thickness. After the invention of the collar (in 1555) struck coins had an edge, unlike hammered coins. Striking with a collar formed an edge that could be either smooth or have reeding. Infrequently this reeding was called milled edge, but this was an incorrect term. The screw press formed the edge, but when it was operated by man the coins were usually of small diameter and had shallow relief.

Source of power changed.  To strike larger coins (or deeper relief) more pressure was required of the press. The balance beam became longer, weights were added to the end to effect more pressure, and the number of men increased or horses used. This style of the screw press was called a fly-press, because of the momentum of its spindle advancing down and up, and the beams rapidly flying around the press. (Hand-operated fly presses of varrying sizes are still in use in some modern metalworking plants. They can be used to try out new equipment before it is installed in a power press.)

Later the power came from water power, and by the end of the 18th century, by

steam power. Although the knuckle-joint press was invented in 1817 by Diedrich Uhlhorn in Germany, it did not immediately replace the screw press. It was learned that it was easier to electrify a knuckle-joint press by electric motors than to electrify a screw press. Thus the screw press was only phased out of production with the rise of electricity and electric motors (following 1890).

Even so, screw presses were still used for striking medals well into the 20th century (even at the Paris Mint). Screw presses finally were replaced when hydraulic presses (developed during World War I) became widely available thereafter.  See presses and pressroom practice.

                                                           

          How A Screw Press Was Operated Manually         

                                                          

     "A coining machine [screw press] resembles in a      

 massive way the old-fashioned press used for copying     

 letters or embossing a seal on papers. The dies were     

 inserted near floor level and the lower fixed to the     

 foundations; the upper die to the base of a vertical     

 column [spindle] with a spiral engaged to the housings.  

 Two arms, each 6 feet long, loaded at the tip with 300    

 pounds of lead and furnished with two ropes, projected   

 from the top of the column at about waist-height.        

                                                          

     "Normally four labourers, hauling on these ropes with

 the utmost violence of which they were capable, sent the 

 column and die spinning down on a blank; as it rebounded 

 it was [brought] back by a lighter rope to prevent double-

 striking, and wound up for a fresh blow. A [pressman or  

 coin setter], seated in a pit before the opening, flicked

 the struck coin away with his middle finger and with     

 index and thumb set a fresh blank on the lower die.       

                                                          

     "The ponderous machines worked at the astonishing    

 pace of a blow every two seconds. The toil was exhausting;

 a crew of seven was assigned to a press, of whom three   

 rested while the four worked a twenty-minute spell. They 

 were reckoned to labour at the press for five hours only 

 of the working day of ten; the rest of the day was spent 

 in fetching and carrying and odd jobs."                  

                           –John Craig, The Mint,        

                             CH17 {1953} p 164.                                                                      

How the screw press was used.  Three (or more) men were required to operate a screw press. One sat facing the press and manually fed the blanks and removed the coins after they were struck. Sometimes he sat in a pit that allowed him to get closer to the striking. He was called the coin setter. (Automatic feeding and delivery was installed on screw presses following 1790.)

Two or four men above him – called the spinners – pressed the balance beam at opposite ends pressing in opposite directions. As the men pushed against the beam the spindle on the press moved downward the housing containing the die. It was easy at first until the die met the blank, then it required great strength to press even harder to advance the die into the blank forming the design. With practice the team of men could get their rhythm synchronized until the momentum drove the spindle down and back in rapid succession.

Longer arms of the beam and heavier weights at the end gave them greater

leverage to increase the pressure for the final squeeze forcing the dies into the blank as far as necessary. To achieve even greater pressure it required more men on each end of the beam. The larger the diameter of the coin the greater the pressure was needed. A crown size coin could require as many as eight men, four on each beam. (The use of a horse could replace as many as four or six men.)

After they pressed the coin with as great a force as they could apply, the spinners

reversed themselves and pressed on the beam in the opposite direction to raise the die housing on the spindle. Sometimes they attached leather straps to the beam to pull the beam back, if they preferred to do that, since raising the die housing did not require great strength to return it to open position.

History of the screw press.  The concept of screw press had been used in mid 1400s for both printing and squeezing fruits and olives. The first screw press for striking numismatic items was developed by an Italian, Donato Bramante (1444-1514) in 1506 for striking lead seals for Pope Julius II (1503-13). This principle was described and illustrated by Benvenuto Cellini in his work on goldsmithing and he used a screw press in 1530 for striking his own lead seals for Pope Clemente VII (1523- 34).

In Augsburg, Germany in 1550, Max (or Marx) Schwab improved on the screw press and attempted to sell this to the mint in Venice. Unsuccessful there he did exhibit his "engines" (a term used for screw presses, hubbing presses and rolling mills) to a French ambassador leading to the purchase by King Henry II, for the royal mint in Paris (delivered in January 1551). Later Spanish emissaries visited Schwab to learn of his techniques and machines.

The screw press was installed at the Paris Mint. An employee there, Eloye Mestrel, learned its operation very well, but became dissatisfied with the lack of acceptance of the new press by moneyers who feared their hammer technique would be replaced. Mestrel fled, in 1561, to England and set up a screw press at the London Mint. Following this early use in Italy, Germany, France and England, use of the screw press spread to other mints throughout Europe. Despite an attempt to use roller dies to impress blank strip, later to be cut out (the process known as taschenwerke), the screw press thrived and was widely used for striking.

No major improvements occurred until 1786 when an Italian engineer,

Francesco Comelli, at the Bologna Mint invented a collar and ejection system to be used with the screw press. This would strike coins and shape the edge with one pressing. A few years later, two engineers at the Paris Mint devised a way to feed the blanks, drop the blank in the collar, strike and eject the piece, then remove it in one cycle while the press was manually operated. Jean-Pierre Droz and Philippe Gengembre were these innovators.

It was for Boulton and Watt, who hired Droz away from the Paris Mint in 1789, to devise a way to incorporate all these innovations and run the press by their steam powered engines. This was an outstanding undertaking and a landmark in the history of coining!

Boulton and Watt made full use of the screw press, with Comelli's collar and

Droz's automatic feed and delivery systems, with the power of their steam engines. Not only did they manufacturing screw presses for their own private mint in Birmingham, and by custom striking with these presses, but also to manufacturing these presses for other mints.

Thus the screw press struck coins for nearly 400 years (1505-1898), medals were struck by the screw press well into the 20th century (1530-1914). The press was also utilized to do blanking, and even hubbing until the end of the 19th century. The invention of the Uhlhorn knuckle-joint press, in 1817 in Germany, and its improvement, by Thonnelier in 1836 in France, did not entirely replace the screw press.

It was two events that greatly reduced the usefulness of the screw press: (1) it was learned that a knuckle-joint press with a large fly wheel could be electrified easier than a screw press when electricity became commercially available (after 1883), and (2) improvements to the hydraulic press which proved far more useful for hubbing (and for striking large medals). Screw presses are still in use in tool and die shops for pressing where only a moderate pressure is required, even into the 21st century.

References:                                                                                                                              

C1      {1540} Biringuccio

C24    {1948} Mason

C32    {1954} Singer, 3:338-41.

C36    {1956} Forster

C60    {1974} Goldman.

C64    {1978} Adams.

C67    {1988} Cooper, Chapter 6, pp 51-60.

C69    {1995} DeLorey

CH17 {1953} Craig, p 164.

NC5   {1964} Peck, p 141.

NC11 {1988} Breen, p 708.

NE40 {1984} Junge, p 227.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor