1909 – The beginning of the modern minting process is set in
1909. Prior to 1909 a partial hubbing process was utilized by
the U.S. Mint. This process left the date and mintmark to be
hand punched into each working die. 1909 saw for the first
time, the date engraved into the master die, so that every
working hub and working die carried the same date positioning.
Mintmarks, however, were still applied to the working dies by
hand as each branch mint had a need for dies.
1985 – The U.S.
Mint began punching the mintmark into the master die for all
proof coinage. The last year possible for an RPM on a proof
coin is 1984, however, the last known RPM for proof coins is
1975. In the middle of
1974 the S mintmark punch broke and a new
punch with a new style of S was placed into use. This new punch
was itself doubled resulting in a doubled mintmark on every
working die. The doubling on the new punch wore off fairly
rapidly so even though the punch was used into 1979 the doubling
is no longer seen after 1976.
1986 – The U.S.
Mint began experimenting with a single squeeze hubbing process.
This process eliminates the need to anneal a die and then re-hub
it in order to get the proper depth for striking coins.
1990 – The U.S.
Mint began punching the mintmark into the master die for the
cent and nickel denominations. The last year possible for an
RPM on a business strike cent or nickel is 1989. There are
several known RPMs for the 1989-D cent but the last known nickel
RPM is dated 1984-D.
1991 – The U.S.
Mint began punching the mintmark into the master die for the
dime, quarter, and half dollar denominations. The last year
possible for an RPM on a business strike dime, quarter or half
is 1990. The last known RPM for a dime is 1988-D. The last
known RPM for a quarter is 1989-D. The last known RPM for a
half dollar is 1989-D and
can be found in Mint Sets.
1996 – The Denver
Mint opened its own die shop and began using a single squeeze
hubbing process for cents through quarters. Thus the doubled
die was effectively eliminated. There are a couple of ways for
doubling to occur on the die during the single squeeze process,
but the vast majority of doubled dies are now a thing of the
past. There are some 1996 dated doubled die obverses on the
Philadelphia cent.
1997 – The
Philadelphia Mint began using the new single squeeze hubbing
process for cents through quarters.
1999 – The U.S.
Mint adds the half dollar to the single squeeze hubbing
process. The last known doubled die for the
half dollar is
dated 1992-S and is on the silver proof.
1999 – The U.S. Mint used the old
hubbing equipment to create the SBA dollar coins needed late in
the year and for collector proof sets. A couple of nice
doubled die obverses are known for the 1999-P proof SBA.