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By Albert Sims
Disclaimer: I am doing this mostly from memory and may contain some errors, for which I apologize. Some of the data and numbers I will look up from the ANA correspondence course The MODERN MINTING PROCESS, by James Wiles, Ph.D., a well written and helpful course which I highly recommend for all collectors/dealers especially those who want to collect errors and varieties. Some areas I will not go into because of copyright restrictions and do not want to get myself into trouble. This writing is as of Aug 1998 and does not include any changes the mint may have made sense that time.
The modern minting
process can be broken down into 3 distinct areas, PLANCHET, DIE
and STRIKING, sometimes referred to as the P, D and S system, this
is easy to remember as it reflects the Mint Marks of the three
current mint marks used on modern coinage.
Philadelphia, Denver and San Francisco.
I will cover each
area. one at a time. All mint errors and varieties can be
directly attributed to one of these three
areas of the minting process and can
aid in determining the authenticity
of their existence.
PLANCHET: Most of the cent blanks/planchets are made outside the mint, as is much of the metal for other denominations, but the process is pretty much the same. The metal is carefully processed to assure correct alloy and is rolled into long strips of the proper thickness for each denomination. Each strip is approx. 1300 feet long and weighs between 1,100 and 7,000 pounds. (from ANA book) Every lot is tested and weighed at the mint.
These large coils are placed on a reel and feed into the blanking press (much like a high speed cookie cutter) which in turn “punches” out the blanks. The leftover scrap metal, called webbing is recycled to the vendor for future use. The blanks are then annealed and cleaned. (This procedure is covered quite will in the Course.) At this point the blanks are flat and rough.
The blanks, once
annealed, cooled, washed, cleaned and dried, proceed to the upsetting mill
which “squeezes” the blanks edges to give it a raised edge/rim. This also
reduces the diameter so it will fit into the die collar during the striking
process, it also “ helps protect the design and prolong the coins’ life
and helps the coins stack neatly” (ANA correspondence course). Once the
blank has upset edges it is then called a planchet. Although the terms
“blank” and “planchet” are used synonymously, they are different
and mean different things and are often referred to as type I and type
II planchets.
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DIES: The first step in making the dies is the design, artist create the design in on a plaster model approx. 8 inches in diameter. The plaster model is then covered with rubber to make a rubber mold which is then cast with epoxy to make a shell. This process has replaced the “galvano” method of producing the shell.
The epoxy shell is then sent to the die making area. Since the shell is much larger than the coin its design must be reduced to the size of the actual coin. This is done with the use of the “Janvier transfer reducing machine” which traces the design in its reduced size to the master hub, sometimes called a “hob”. This process takes days to accomplish. This and the next steps in the die making process are very critical as each and every one can affect the final product.
The master hub is then used to make master dies. This process is called “hubbing”. Using a hydraulic press the master hub is pressed into a piece of die steel to produce a master die.
This hubbing process (and all later hubbing process) use to take several days and many impressions to get the right depth of the impression to the master die. After each hubbing the die had to be annealed because it could become brittle and crack or break. This is also the first place where a doubled die could occur if the master hub is not perfectly aligned with the master die. (because of modern technology, the mint now uses a single hubbing process which eliminates the possibility of doubled dies and speeds the hubbing process.)
Master dies are
then used to make working hubs. Working hubs are used to make working dies
which are used for minting coins.
Again, another area
where doubled dies can occur. Depending where in this process doubled dies
are created will affect the amount of coins struck from the die or dies.
Also mint marks are now part of the plaster model, eliminating repunched
Mint Marks (this process was changed in 1985/86 for proof coins and
in 1990 for cents/nickels (business strikes), 1991 for the dime, quarter
and half dollar (business strikes). {ANA correspondence course})
STRIKING PROCESS: The finished planchets are fed to the coining press via feeder tubes, the planchets drop into the feeder fingers (metal slides that eject the coins from the coining chamber while depositing the next planchet into the coining chamber.) The coining chamber consist of the lower die or anvil (usually the reverse), the upper die or hammer, the collar and the feeding fingers. The anvil or bottom die remain stationary during striking and only moves when the coin is being ejected. The hammer die is the die that moves down to strike the coin.
The newer coin presses can hold up to 4 sets of dies and can make up to 720 strikes per minute striking with a force between 30 and 100 tons depending on the denomination of the coin being struck (ANA correspondence course)
The coins are collected in bins and then put through a series of sizing screens or “riddles” removing under sized or over sized coins and returning them to the scrap bin. Riddle screens are also used at other stages of the minting process.
Coins are then
weighed, counted and bagged for shipment to the Federal Reserve depositories.
Local banks then request their coins from these facilities.