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V11 2008 INDEX
E-SYLUM ARCHIVE
DICK JOHNSON ON COIN REEDING TECHNOLOGY
Dick Johnson forwarded this detailed report on minting
technology surrounding edge reeds. -Editor
Let's define some terms.
A reed is the wave from the top of one raised ridge to the top of
the next ridge. Reeding is the collective term for all the reeds.
The ridge has its own term knurl and collectively known as
knurling . The indentation is known as a flute. A reed is
one knurl and one flute. Reeds are created by the collar when
struck in a coining press. The collar is a large flat ring with a center
aperture nearly the exact size as the coin being struck. Both dies
have to enter this aperture and retract. The clearance between dies
and the collar wall is thousands of an inch. (If the clearance is too
great this is an area where metal will escape as flash this is how
wire rims are formed.)The collar has grooves cut on the inside wall of the aperture these form the knurls on a coin. The grooves are cut by a tool-and-diemaker . The shape of the knurl depends upon the cutting tool he uses.
When a coin is struck the metal in the blank expands to fill all the modulated relief in the obverse and reverse die, all the design devices and all the lettering. At the same instant the blank expands up against the collar. All things being right like the correct mass of the blank and the correct pressure of the press metal flows into all the openings in the collar to fill and form all the coin's knurls. That's the reeding. If there is not enough metal to completely flow into the grooves the tops of some of the knurls are incorrectly formed. Usually increasing the pressure of the strike will remedy this problem.
At this point in the press cycle the coin is frozen in its chamber. It must be removed ejected by one die pushing it out. There is a mechanism built into the press, an eccentric wheel with a kickout pin pushes the die past the edge of the collar so the struck piece is freed.
A coin with reeding must easily slide out during ejection. Other than a blank wall aperture forming a smooth edge coin reeding is the only edge treatment where this can occur. Obviously, lettering or any edge ornamentation, or even diagonal lines cannot be ejected in a coining press. (Edge lettering is an entirely different subject, completely different from our discussion here of reeding.)
We should also mention interrupted reeding. This is the technology to place a smooth area on a reeded edge piece. A smooth area is useful for placing hallmarks, edge lettering and such, in contrast to the entire circumference with reeding, which numismatists call fully reeded. It is created by leaving the inner aperture wall blank where a smooth area is desired.
In 1965 the Franklin Mint used this concept for a great commercial use. They were striking gambling tokens of similar size for many casinos in Las Vegas. They learned that patrons were carrying these tokens to other casinos. They needed a quick way to identify host tokens from those of other casinos. By using a different collar with unique pairs of reeded and blank areas for each casino the tokens would stand out when laid in rows. Joseph Segel, as president of Franklin Mint, received U.S. patent 3350802 in 1967 for this invention.
As mentioned in last week's E-Sylum, reed counting can be a diagnostic to distinguish two different coins. U.S. Assay gold coins were mentioned. A more modern example is the 1968 Canadian dime . The Canadian Royal Mint could not supply a large order for the 10-cent coin that year. In addition to what it produced it asked the Philadelphia Mint to strike the Canadian dime as well. The Ottawa Mint supplied obverse and reverse dies to the Philadelphia Mint, but did not furnish an accompanying collar. Philadelphia pressmen grabbed a collar off the rack intended for a U.S. dime, since both were of the same dimensions. That collar had a different reed count and this is the only diagnostic to differentiate which mint struck any 1968 Canadian dime.
Reeding has some beneficial advantages. It aids the blind (a reeded quarter is thus different from a smooth edge nickel of similar size), and it aids everyone in picking up and holding on to the coin. There are also some advantages in coin sorting and counting machines as well.
Placing reeding on coins is almost as old as the use of the collar in coining itself. The collar was first used by Aubin Olivier using a screw press at the Paris Mint in 1555. But we dont know which was the first coin with a reeded edge. It might have been influenced by Sir Isaac Newton who was a strong opponent of coin clipping. As Mintmaster at Britains Royal Mint he sought ways to combat shaving or clipping the edges of coins. The reeded edge was created to halt scraping or filling off metal from coin edges to melt the filings.
Dick Johnson adds:
QUERY: For knowledgeable E-Sylum readers, I would like to
ask: What was the first coin with a reeded edge? It would probably date
late 1500s or early in the 17th century. (And dont tell me ancient coins
were reeded those serrations are something else.) I would like to know the
first diestruck coin with reeding.
Wayne Homren, Editor
The Numismatic Bibliomania Society is a non-profit organization promoting numismatic literature. See our web site at coinbooks.org.
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