U.S. Mint at San Francisco, Coining Press Room

by Mike Unser on April 17, 2013 · 4 comments

Pressed penny machines… You gotta love them. Stick a penny into the slot, pick your design, start cranking, crank some more and then a little more. Eventually, out pops your flattened souvenir.

San Francisco Mint Coin Presses and Operators

San Francisco Mint Coin Presses and Press Operators at work Frank Romero (background), Michael Yu (middle) and Michael Lu (front). Many more photos are below.

The mechanics are kind of similar with presses at the U.S. Mint at San Francisco, but the scope of Mint presses are obviously quite different and blazingly fast.

How fast? The SF Mint on average can produce about 200,000 collectible proof coins per day. More than 20.1 million were struck there last year alone.

In the mechanics, a blank slides into position flat side down so it can get squeezed between two vertically placed dies. These dies bear negative images of the heads and tails side of a coin. When the press applies some 90 tons of pressure between them, the blank flows like putty and accepts their designs. The blank doesn’t flatten like a penny in a souvenir machine as a surrounding collar restrains its expansion. That collar also creates a coin’s reeded edge or imparts the edge-incused lettering on Native American $1 Coins and Presidential $1 Coins.

If the terms "blanks" and "dies" are confusing or you’d like to see how they are prepared at the San Francisco Mint, check out the linked articles in the far right column. They are listed third and fourth under the series of articles about my visit at the SF Mint.

This fifth article describes how the San Francisco Mint turns blanks into coins. I really enjoyed this part of the tour. The SF Mint not only strikes proof coins for collectors but also millions of bullion American Silver Eagles each year. Seeing them produced and stacked by the thousands was something else.

Producing Coins at the U.S. Mint at San Francisco

In a large L-shaped area that San Francisco Mint employees call the Coining Press Room, there are nearly 20 presses lined up against walls. But before blanks get to them, they first receive some special attention. Though they have already been through the Treatment Room, the blanks are manually washed, dried and buffed. That’s quite an undertaking with the millions of proofs minted each year.

Washing and Drying Rooms for Coin Blanks

SF Mint Blank Wash Room

Herby Lam and Linda Lau in blank wash room

 

Sey Ting Yen towel buffing blanks

Sey Ting Yen towel buffing blanks

 

Michael Yu racking buffed blanks

Michael Yu racking buffed blanks

 

Linda Lu racking blanks for the press

Linda Lu racking blanks for the press

 

Blank staging area in Coining Press Room

Blank staging area in Coining Press Room. These are blanks in line to get pressed.

Die Vault

Every coin die, whether new or old, comes from and goes back into the die vault for storage and security.

Die Vault Storage Area at SF Mint

Die vault storage area at SF Mint

 

Coin Dies from SF Mint

Coin dies from SF Mint

Installing Coin Dies

Specially designed tooling kits are used to house dies which then fit inside coin presses.

Die Tooling Kit

Die Tooling Kit

 

David Atienza assembling die tooling

David Atienza assembling die tooling for obverse of an American Silver Eagle

Proof Native American $1 Coins and proof Presidential $1 Coins receive their edge lettering from a three-segment collar. Each segment bears a unique part of the edge inscription in raised letters. These segments are custom designed with slots so they cannot accidentally get placed into the die housing out of order and create coin errors.

2013-S Proof Woodrow Wilson Presidential $1 Coin Die (Obverse) Installed into Collar

2013-S Proof Woodrow Wilson Presidential $1 Coin Die (Obverse) Installed into Collar

In a coin press, the obverse Presidential $1 Coin die in its housing shown above behaves more like an anvil. The reverse die, shown and assembled in the die housing kit below, acts more like the hammer that pounds the anvil.

2013-S Proof Presidential $1 Coin Die (Reverse) and Die Tooling Parts

2013-S Proof Presidential $1 Coin Die (Reverse) and Die Tooling Parts

 

SF Mint Employee Assembling Tooling for 2013-S Proof Presidential $1 Coin Reverse Die

SF Mint employee assembling tooling for reverse of Presidential $1 Coin die

 

2013-S Proof Presidential $1 Coin Die (Reverse) Installed

2013-S Proof Presidential $1 Coin Die (Reverse) Installed

 

Coin Press Feeding

Prepared blanks are manually fed into loading magazines. The press feeding system takes a blank from a magazine to strike and produce one coin at a time.

Carlos Dumpit loading magazine for coin press feeding system

Carlos Dumpit loading magazine for coin press feeding system

Clicking on the photo below shows how the blanks look right before they’re made into coins.

Planchets for 2013-S Proof Native American $1 Coins

Planchets for 2013-S Proof Native American $1 Coins

SF Mint Laser Machine for Die Collar Engraving & Machine Shop

Jumping out of the Coining Press Room for a second, this is a laser machine that does the engraving for the three-segmented die collars discussed earlier. It engraves the stars, letters and numbers for edge letter collars used on dollar coins.

Laser machine for die collar engraving

Laser machine for die collar engraving

Also worth noting and in an area of its own, the U.S. Mint at San Francisco has its own machine shop that is responsible for modifying production tooling, process improvement support and design and engineering improvements.

Machine Shop at San Francisco Mint

Machine Shop at San Francisco Mint

Coin Presses at San Francisco Mint

Returning to the Coining Press Room, the following several photos show some of the SF Mint presses and their internal components.

William Tan operating coin press

William Tan operating coin press

 

Internal view of Coining Press at SF Mint

Internal view of Coining Press at SF Mint. Notice the coin in the middle.

If you look closely at the photos directly above and below, you’ll notice the reverse die at top center and the obverse die at bottom center.

Another view of the internal components of a Coin Press. This one shows a coin in the center that has been struck.

Another view of the internal components of a Coin Press. This one shows a closer look at the pressing area by the coin.

Coins getting pressed at the U.S. Mint at San Francisco don’t shoot out into bins. They instead slide into custom coins trays to preserve their condition.

2013-S Proof Native American $1 Coins produced on coin press at SF Mint

2013-S Proof Native American $1 Coins produced on coin press at SF Mint

2013 American Eagle silver bullion coins produced on coin press at SF Mint

2013 American Eagle silver bullion coins produced on coin press at SF Mint

 

Lynn Lobb inspecting bullion product

Lynn Lobb inspecting bullion product

Pressed Coins Ready for Packaging

Finally, here are finished coins. These are really something to see in person.

Trays of 2013 American Eagle silver bullion coins

Trays of 2013 American Eagle silver bullion coins

 

Trays of 2013-S Proof Native American $1 Coins produced at SF Mint

Trays of 2013-S Proof Native American $1 Coins produced at SF Mint


Newly produced 2013-S Proof America the Beautiful Quarters

Newly produced 2013-S Proof America the Beautiful Quarters.

With trays of proof coins readied, they will move to the packaging room for automatic placement into plastic lenses to create proof sets.

Upcoming Article About the U.S. Mint at San Francisco

Please return Wednesday, April 24, for the next article in a several part series describing my visit to the U.S. Mint at San Francisco. We’ll take a walk though the automated Packaging Rooms responsible for placing coins into lenses and boxing proof sets up for shipping. We’ll also see some of the quality assurance equipment and staff.

Lenses automatically packaged for 2013 Proof Sets

Lenses automatically packaged for 2013 Proof Sets

Article Series About U.S. Mint at San Francisco

{ 4 comments… read them below or add one }

Joe April 20, 2013 at 5:57 pm

It’s amazing the mint can pump out that many coins a day with all the procedures they go through.

Clara April 21, 2013 at 12:36 am

Thanks

Paul St.Julien April 21, 2013 at 5:05 pm

I love learning how things work. I’ve seen several YouTube videos on the operations at the US Mint. It was nice to see individual pictures to study for as long as I needed. Thanks…

ben April 23, 2013 at 8:37 pm

I use to be a pressman at the U.S. Mint on Hermann Street, during the 1776-1976 Bicentennial program in 1974-’75. I pressed the Eisenhower silver dollars with an occasional stint on the quarter and half dollar presses. It was one blank at a time. These coins were not for public circulation but for sale.

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