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Knuckle-joint Press

Knuckle-joint Press.  A press whose action is based on a hinged joint and flywheel. This type of press has a relatively long extrusion dwell, particularly useful for preventing the springing back of the surface metal. This type of striking is ideal for both numismatic and medallic items, in fact more of the world's coins and medals have been struck on knuckle- joint presses than any other.

Coining presses.  The first knuckle-joint press for coining, the Uhlhorn, was invented by Diedrich Uhlhorn in Germany in 1812 (and patented in 1817). This was intended to replace the screw press, which had been used for over 300 years (but was not until the end of the 19th century when knuckle-joint presses could be electrified with greater ease than screw presses that the screw press was ultimately phased out of any coining mint).

From the beginning Uhlhorn presses had automatic feed and delivery systems. It also incorporated the collar for forming the edge treatment of struck pieces, either smooth or reeded. Uhlhorn established a factory in Grevenbroich, Germany in 1817 for the purpose of building presses for minting coins and it continued in operation until at least 1880.

Although Uhlhorn was preceded by a hand cranked knuckle-joint press devised by Russian mintworker at the Saint Petersburg Mint, I.A. Nevedomskiy in 1811, his manually operated press was never placed into production. A drawing has survived however.

In 1836 the Uhlhorn press was modified by a Frenchman, who created the Thonnelier press, and mints of the world used either or both type presses for over 150 years and both are still in use. A toggle-action press was evolved from the knuckle-joint and all coining presses built after about 1860 are optional knuckle-joint or toggle-action mechanics. German and English firms have dominated the manufacture of these coining presses (but some coining presses have been made in America, Austria, Belgium and Sweden).

Knuckle-joint presses were originally powered by steam engines (infrequently by water power) until 1890. Thus steam engines (as Boulton and Watt's engines) were just as necessary for mints as Uhlhorn's coining presses. The power was transferred to the press by belting. After 1890 most all presses were electrified and driven by electric motors. America's Third Mint in Philadelphia built in 1901 became the first all-electric mint in the world; twelve Morgan & Orr knuckle-joint presses were moved from the old Second Mint to the new mint and electrified.

Medal presses.  Presses for striking medals can be either knuckle-joint or hydraulic. The advantages of the knuckle-joint are a sharper blow, a longer extrusion dwell and higher production speeds.  Hydraulic presses, while slower in production, can develop a more forceful "squeeze" displacing more surface metal with each press cycle making them more suitable for high relief multiple struck medals with fewer blows and intermediate annealing necessary.

Knuckle-joint is sometimes called knee-action.  See presses and pressroom practice.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


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