VOCABULARY TERM: PRESSES, PART 2

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.

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.

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.

To read the complete entry on the Newman Numismatic Portal, see:
Presses and Pressroom Practice (https://nnp.wustl.edu/library/dictionarydetail/516539)

To read the earlier E-Sylum article, see:
VOCABULARY TERM: PRESSES, PART 1 (https://www.coinbooks.org/v27/esylum_v27n33a17.html)

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