A prototype visual inspection system for dies is being tested at
the San Francisco Mint that Mint officials say will eliminate
production of errors resulting from wrong dies being mounted into a
coinage press or dies oriented in the wrong position relative to each other.
When Coin World visited the production floor of the San
Francisco Mint May 14, the Newton Press Die Inspection System was in
use on a Gräbener coinage press striking Proof 2012-S Benjamin
Harrison Presidential dollars for the four-coin 2012-S Presidential $1
The Newton system (www.newtonlabs.com/, located in
Renton, Wash.) is intended to eliminate the possibility of rotated die
errors from planchets being struck with dies that are out of
orientation from obverse to reverse, according to Joseph Vasquez, a
mechanical engineer in the San Francisco Mint’s coining division.
The inspection system will also eliminate any mule error
possibilities, Vasquez said. A mule error is the result of a wrong
pairing of dies in a coinage press.
The United States Mint has struck only a few mule errors. The most
prominent mules recently produced are the Philadelphia Mint struck
(2000)-P double-denomination mule errors that paired a State quarter
dollar obverse die with a Sacagawea dollar reverse and were struck on
manganese-brass clad dollar planchets on a press dedicated to dollar
coin production. The coins have no date but carry denominational
inscriptions on both sides.
Eleven examples are known of that style of mule error, from three
different pairs of dies.
Vasquez said the Newton system will visually inspect a pair of
dies and catch any defects before production.
The obverse and reverse coin art for the coin to be struck is
digitally programmed into the system. Dies are mounted in the press
and the visual inspection system scans the dies to ensure that the
dies in the press match the programmed designs, Vasquez said.
The inspection system will also digitally scan the dies to ensure
they are mounted in the correct location and oriented correctly, so
that coins struck from them are oriented correctly from obverse to reverse.
Although the inspection system is currently being used only for
dollar coin production, its use may be extended to other
denominations, according to Vasquez.
The Proof Presidential dollars are being struck on presses with
the dies striking vertically.
Vasquez said the dollar dies are mounted in the coinage press with
the common Statue of Liberty reverse in the upper or hammer die
position, and the Presidential portrait obverse die in the lower or
anvil die position.
Edge inscription process
The edge inscription on the coins is imparted during striking by a
three-piece segmented collar.
The three-piece segmented collar die carries different portions of
the edge inscription, enabling the inscription to be formed during
striking. Segment A carries the raised date and Mint mark flanked on
each side by two five-pointed stars. Segment B carries one star
followed by the motto E PLURIBUS UNUM. Segment C carries the remaining
eight of 13 total stars.
The individual elements of the edge inscription are raised on the
collar die segments; the raised elements form incused inscription
elements on the coins.
The edge segments come together during striking to form the
inscription, then spring apart to permit the coin to be ejected from
the press with no damage to the newly formed inscription. The anvil
die moves upward slightly to facilitate ejection of the coin.
A similar three-piece, segmented collar was used to form edge
devices of the Indian Head gold $10 eagle and Saint-Gaudens gold $20
double eagle of the first half of the 20th century.
The three pieces of the segmented collar are coded by number of
slots: having no slot, two slots and one slot. The coding ensures that
only one of each of the three collar segments is used and that they
are properly seated in correct order in the die housing, thus
preventing an out-of-order edge inscription.
Using this system of slots is intended to prevent the kind of
error that occurred in 2007. An unknown number of 2007-S Thomas
Jefferson Presidential dollars were struck with two of the three edge
collar segments out of sequence. The second and third segments were
inadvertently switched, resulting in the edge inscription appearing in
the wrong order: the date and Mint mark, the motto IN GOD WE TRUST and
the legend E PLURIBUS UNUM. The order of the latter two segments
should have been reversed, with E PLURIBUS UNUM appearing first, then
IN GOD WE TRUST.
The edge inscription is placed on circulation-quality Presidential
dollars in a different process. The inscription is added to struck
coins as a separate production step. ■