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Collar

Collar.  (2) A large flat disk or ring – made solid or of multiple segments – with an opening in the center, an aperture of prescribed diameter and machined on the inner wall surface to the requirements of the pieces to be struck. It is the collar that imparts to all coined pieces the shape of their edge: smooth or reeded. All coining dies are collar dies, that is, they are made to strike coins inside the collar, the neck of each die is slightly smaller than the width of the aperture. Also, all coining presses require some form of collar, and have for as long as coins have had uniform edges, certainly since the 1400s. In contrast, medal presses have employed collars – some still do – however, since 1900 most medal presses have utilized open face dies that do not need collars.

Collars can only be used with collar dies whose diameter will match the aperture in the collar. The neck of the dies must be one or two thousandths of an inch smaller than the collar aperture. The measurements must be precise to allow the dies to enter the aperture, strike the blank and retract. Also, the blanks must be an exact diameter to fit inside the aperture, again, several thousandths of an inch smaller than the collar aperture. If not the blanks will jam in the press.

Types of Collars.

 

cone collar – A collar with minute draft or bevel of the aperture        wall for the ease of ejecting the struck piece, wider at the bottom            where the struck piece exits.

lettered collar – Always a segmented collar with incised lettering             on the inner wall of the aperture to form raised lettering on the edge of       the struck piece.

reeded collar— A collar of any kind with serrations on the aperture’s inner wall that forms the reeding on the struck piece.

ring collar –  A one-piece collar that is one segment obviously with             the center aperture.

segmented collar – A collar of multiple segments, usually three,    called a tri-segmented collar, which must be dismantled to eject the          struck piece with raised lettering or such.

smooth collar –  The aperture wall has a smooth surface on such a collar to produce a smooth edge struck piece.

split collar –  A collar of several segments, same as segmented             collar.                                    

toggle collar – 

Function of the collar.  The collar acts to restrain the outward flow of metal when a blank is struck, at the same time forming the surface of the edge. The coining cycle can be described as follows noting the function of the collar:  A blank is brought into coining position by a feeder mechanism. The blank is pushed inside the collar aperture by one of the dies as they enter the aperture during the beginning of the press cycle. The two dies and the collar form the coining chamber. As the dies extend to their fullest length they impress the blank with their full force, driving the design into the surface of the softened blank.

Metal on all surfaces of the blank – both sides and the edge – flow into the

design cavities of the dies and up against the inner walls of the collar. Pressure of the press must be established during setup so that the preformed (upset) blank has enough metal to flow into all design cavities with enough left over to flow up against the wall of the collar. All this happens instantaneously.

If the pressure is not great enough, or the blank is light weight (lacking mass), there is not enough metal to flow into all cavities or into the shape of the collar

the piece will not be fully struck up (and could look like an uncirculated worn coin, what a collector would call a die trial). The edge may not be perfectly formed as well, missing knurls or ridges in the reeding.

On the other hand, if the pressure is too great, or the blank is overweight, the metal from such a blank will fill all the cavities then still have excess metal left over to

flow into the only open place available to it: the tiny space between the die and the collar. This creates on the struck piece a fin, or burr – what an American collector would call a wire edge and an English collector would call a knife edge – but what a machinist or pressman would call flash.

When the dies are fully extended, the piece is fully struck up, but at this point the piece is "frozen" up against the collar wall. To dislodge it the ejector mechanism is so engineered to propel one of the dies (usually the opposite die from the one that pushed the blank into position) to push the struck piece out of the collar aperture from its "frozen" position.

It is for this reason that the edges of pieces struck in a coining press can only be

smooth or reeded – they must be capable of being ejected from the collar. Thus the collar can only be smooth or reeded; the reeding, however, can take many forms – as different number or widths of knurls (ridges) and flutes (furrows) together forming the reeding. Or the edge may have a combination of smooth and reeded areas (interrupted reeding).  See reeded edge.

The size, mass and hardness of the collar is important, as the collar must restrain the constant pounding of the metal blanks up against its aperture wall. It accomplishes this by the mass of the collar. As the diameter of the struck piece increases arithmetically, the diameter of the collar increases more so. Two inch coined pieces require a 6-inch diameter collar; a 4-inch coined piece would (should) have a collar as wide as 12 inches.

Collar wear.  With very long and continued use the aperture in a collar will grow larger and brighter from wear. The inner wall becomes brighter (like the face of a die) from the constant action of the scraping of the struck metal pieces being pushed out of the aperture.

Numismatic writer Walter Breen reports that cent collars wear the most (undoubtedly so from multi-billion coinages). Cents struck before 1972 used a collar with a 0.747-inch aperture. After 1972 (with the new copper-coated zinc composition) the collar size was increased to 0.749-inch. Breen reports that cent collars at the branch mints (Denver particularly) are not discarded until their aperture enlarges to 0.753-inch.

Striking a blank with pre-formed edge lettering or engrailment.  Coin blanks, which first have been treated by the Castaing or canneluring machine with lettering or engrailment, can be struck within a collar but extreme care must be employed. First the blanks must be uniform in size and shape, upset if possible.

When striking these pre-formed blanks the collar to be used must have a smooth chamber wall and a slightly oversize aperture. The pressure must be enough to effect the obverse and reverse impression, but not great enough to mash or deform the edge containing the sunken engrailment or lettering and very slightly bowed edge. The impact against the collar will straighten the edge while the sunken lettering or engrailment remains intact. There may exist a very minute overhang of metal at the top of the letters where metal flowed into these tiny furrows.  See lettered collar.

Segmented collar is a special collar made of several segments to effect raised lettering or other reasons. The collar is made of three, four or six sections – usually three – that fit into a retaining ring and held in position by a collar plate.

Segmented collars have been employed for large medals and a smooth edge, however the most important use for the segmented sections are to impart raised lettering. The process is slow in that the assemblage has to be broken apart after each subsequent blow, or to repeat the process for the next piece. Impractical for long production runs, it is more often used for very exotic medals – the raised lettering on the edge places it in a class above all others. The required tooling and additional press time makes this an expensive procedure.

History of the collarWe really do not know who used the first collar for coining. Perhaps it was Aubin Olivier, who, in Paris in 1555, attempted to create an engraved edge with a special collar. It had to have been in use before 1683 (when Thomas Simon created his petition crown). But it was for Jean-Pierre Droz to have improved it even more in Paris in 1683 when he developed the segmented collar (virole brisée). Droz brought the technology with him to the Soho Mint when he was hired by Matthew Boulton in 1789. Here the collar was employed to its fullest extent and changed little since then.

The use of a collar was one of the secrets of early coining. Mintmasters, until the mid nineteenth century, would require all mint workers not to reveal the mechanics of such mechanical devices to anyone outside the mint. This was thought to have helped prevent counterfeiting. The penalty for disclosing the existence of a collar was to have a hand cut off.

References:                                                                                                                        

C66 {1988} Cooper pp 101, 170-73, illus.

NC8 {1988} Breen.

Also (Droz, Jean-Pierre) Rapport Fait a la Classe des Sciences Mathématiques et Physiques de L’Institut National, Sur Diverses Inventions de Jean-Pierre Droz, Relatives à l’art du Monnoyage. Paris: L’Institut National, Niv?se an XI (December 1804).

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


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