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Edge Rimming

by Denis R. Cooper
The Art and Craft of COINMAKING, A History of Minting Technology
Extract on Edge Rimming: p.101-106

To satisfy the insistent demands for a method of making coins which would prevent the abuse of clipping, a clearly struck coin edge was needed. Various designs were tried - plain, reeded or milled, lettered or ornamented - and engraved around the edges of the blanks, or the coins, using differing techniques. Sometimes the designs were incuse, or cut into the edges, and sometimes they were embossed, or raised. Initially attempts were made to strike coin edges in collars, but these could only produce either a smooth or reeded edge simultaneously with the striking operation. An alternative was to roll the blank, or coin, between engraved dies, either before or after striking.

In 1555 in Paris, Aubin Olivier attempted to use a screw press to produce an engraved edge in a special collar, split radially into three parts, and although this method appears to have been effective it was very slow, and ultimately abandoned [Look at: 8 Henri d'or à la Gallia, piéfort with rimming, 1555 ]. A hundred years later, in 1663 in London, Thomas Simon made another unsuccessful attempt to produce lettering around the edge for the so-called Petition Crown for the coronation of Charles II. This trial was for a coin 40 mm in diameter and 3.5 mm thick with a circumference of 126 mm, Fig. 111.

Fig.111: Simon's Petition Crown shewing the colar B, engraved insert A, and Legend C

Simon must have assembled the collar and the bottom die together, and inserted an engraved band and the blank with the top die resting on it. Presumably he then placed this complete assembly between a pair of flat plattens in a screw press. After being struck, and impressing both faces and around the edge, the coin would have had to be forced out of the collar together with the band, probably by using the bottom die. Immediately the coin came out of the collar, the engraved band would have sprung off the coin edge leaving it with a legend of some 35 words in two lines. Simon must have used the very largest press the Mint could provide. He took a long time to produce his coin, and Pepys observed "how good they (the coins) are in the stamp and how bad in the money for lack of skill to strike them", implying that the engraving was good but the striking was poor. Not a surprising comment as even by this time there were very few mints which could strike a 40 mm diameter coin in one blow.

Methods which involved rolling-in edges either before or after striking were the only options. The new rimming operation rolled the blank through half a turn between two engraved plates or dies, so that each plate marked half of the edge. There are recorded details of the machine introduced in Paris by the French engineer, Castaing, about 1680. It had a copper base plate mounted on a work bench and on this there was a slide which held one of the engraving dies; the second die was set in a straight edge fixed on the opposite side of the base plate. The slide moved backwards and forwards in a line parallel to the straight edge. A rack was attached to it and this was engaged by a pinion on a shaft rotated by a crank handle. The operator withdrew the slide to one end, inserted a blank, and moved the rack forward so that the blank rolled halfway round its edge, Fig.112.

Fig.112: Diderot and d'Alambert Encyclopedia 1763: Rimming Machine

Diderot's sketch shews the edge-engraved blank falling through a slot in the table into a container beneath. It looks as though it could have been possible to insert a fresh blank into the slide to be engraved on the return stroke. The rimming dies could be engraved with milling, or with either incused or raised letters, or with designs. Coins which were rimmed on these machines invariably shew the marks made by the ends of the two die impressions. Castaing undertook a very large issue of coins with incuse edge-marking for Louis XIVth and many dies would have been required but there is no recorded information shewing how they were made; this would have been particularly interesting as the die must have carried a positive impression which would have been difficult to engrave. This little hand-operated machine was copied, modified and developed; one model could mark or rim two blanks at a time between two pairs of dies, and with another an attempt was made to feed the blanks automatically. It is difficult to establish which of these developments was used by Blondeau in his secret process in London in 1662.

Fig.113: Edge Rimming Machine in the Heimatmuseum Stollberg, Harz

One of the last machines of this type remains in excellent preservation in the Heimatsmuseum in Stolberg, East Germany. It bears the date "1763", and its mechanism and the way in which the two edging dies were held together, also the way in which the fixed die could be adjusted, are all very dear. The method of operation was to move the sliding die to the extreme right, and a blank would be held so that on the return movement from right to left it was edged between the dies and dropped through the aperture into a drawer in the machine table, Fig. 113.

It was not essential to use Castaing's layout, which ca me to be known as the "straight line" machine describing the sliding motion of the components. Various trials of rotatory methods were made and one of these was in Vienna where the dies still exist, Fig. 114.

Fig.114: Curved dies used in the rotary Rimming Machine to produce raised leters around the edge of the Maria Theresa Thalers in the Günzburg Mint

Of the two dies, one must have been mounted on a rotating head and the other fixed to the bed of the machine. This idea was further developed in two ways, firstly using a limited rotation of the central die which returned through an arc to rim the next blank, and secondly using a rotating wheel with the blanks being fed continuously between the wheel and the stationary die. This die came to be known as a Segment Block. The reciprocating application could be used for all types of edge marking as each die carried half of the edge design. With the fully rotating wheel only plain rims or incuse designs were possible; there was no way in which the blank could be fed at the precise moment when the leading edges of both dies would be opposite one another, and the rotating wheel carried only a plain groove. Blanks rimmed between the rotating wheel and segment block would show no joins at the ends of the half designs, but if insufficient allowance was made in the depth of the engraving when cutting the dies, the second half of the design would have been shallower than the first.

Günzburg in Germany was an outlying dependency of the Austrian Empire during the eighteenth century, and the authorities in Vienna decreed that a Mint should be estalished in the town. Fortunately there are detailed records of the buildings and some of the machinery, inc1uding an exceptional installation of rimming machines. There were two separate buildings, and at the lower Mint beside the Egelsee, a waterwheel drove, in one drawing five, and in another drawing six, rimming or edge-Iettering machines. Details of their construction is no longer available but Fig. 115 [which is missing] shews the layout of the drive from the water wheels, the mill gearing, together with the rimming machines on an upper fioor. They appear to be rotary, continuously fed machines. The Günzburg Mint production in 1795 was over 9 million pieces, and it was always high, so that so many special machines could be justified. There does not appear to have been a similar installation in Vienna, the capital of the Austrian Empire, and Günzburg must have been exceptional in this respect.

Fig.116: A double drive Rimming Machine

In the records of the Clausthal Mint there is an example of a unique rimming machine, Fig.116. It was used in the first half of the eighteenth century and the caption above the original drawing can be translated as a "curling" or "frilling" machine; it appears to refer to plain reeding. This was an adaptation of a rolling mill in which both rolls were constrained by an idler wheel so that they rotated in the same direction. This wheel connected the gear wheels on the axes of the rolls, and a rocking motion was applied. Each roll carried an insert similar to a Taschenwerk die, with half of the engtaved edge design on each of two parallel tracks. The operator rocked the rolls back until the leading edges of both dies were in line, two blanks were inserted and the rolls rocked forward, so that the dies turned and engraved the edges of both blanks through half a revolution. They were then released. The interesting point about this arrangement is that the blanks remained in one position during embossing and only rotated on their edges. It appears that some form of guiding screw was plovided to hold the blanks upright to prevent outward movement, but nothing to prevent them running towards one another. Apparently this apparatus was not copied in other mints, and in the absence of more precise arrangements for positioning the blanks it was probably difficult to control and not extensively used. Krünitz [Berlin 1805] illustrated the same mechanism, but turned through a right angle, with the wheels, or rolls, rotating about a vertical axis. This was a more practical solution but it does not appear to have been developed.

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