From metal to money: Making America's coins

Road Trip 2010: At the U.S. Mint in Philadelphia, more than 20 million coins are made every day. CNET reporter Daniel Terdiman watches the production process up close.

Daniel Terdiman Former Senior Writer / News
Daniel Terdiman is a senior writer at CNET News covering Twitter, Net culture, and everything in between.
Daniel Terdiman
7 min read

At the U.S. Mint in Philadelphia, a huge bin full of blank dollar coins waits to be fed into a press that will turn them into actual money. Daniel Terdiman/CNET

PHILADELPHIA--Staring at the bin in front of me, stacked high with thousands of dollar coins, it's hard not to make like Scrooge McDuck and jump in headfirst.

Except, of course, that security would grab me and I'd have to deal with having a felony on my record for the rest of my life. Also, there's this small detail: These aren't actually dollars. Yet.

I'm at the U.S. Mint here, the largest mint in the world, and a place big enough--at around 600,000 square feet--that all the rest of the American mints could fit inside. I've come here on Road Trip 2010, and my visit is the bookend to a two-part look at how American money is made. Last week, I got a great behind-the-scenes peek at the production of the next-generation $100 bills, and now I'm here to see how our coins are made.

Making coin at the U.S. Mint (photos)

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From a technology standpoint, it's a good thing I'm here now, rather than, say, 10 years ago. That's because about five years ago, the Mint transitioned from a purely manual production process of engraving in clay to one in which much of the work is done using off-the-shelf software tools like Adobe's Illustrator and Photoshop, plus a few others. Of course, from the perspective of a numismatic enthusiast--or as one of my hosts here put it, a "mint nerd"--it probably would have been better to be here when everything was still done by hand.

Still, as John Mercanti, the Mint's chief engraver, told me, even though much of the work is now done using software tools, there are still designers on staff who prefer to do it the old-school way.

Thousandths of an inch
The good thing about transitioning to tools like Illustrator and Photoshop is that it allows the designers to fix things whenever they want. In the past, a mistake meant starting over and doing an entire drawing again.

Now, errors are easily fixed, and the digital tools let the designers do all kinds of neat tricks that were never possible before: look at 3D models of a future coin, alter their perspective, change angles, maneuver a coin any way they want, and more.

That's critical, Mercanti said, because when crafting a new coin, or any of the commemorative medals made at the the Mint, the "tolerances" the designers are working with are measured in the thousandths of an inch. Indeed, he said that being even one-thousandth of an inch off is tantamount to a Mt. Everest-size mistake, and can mean that the metal in the coin may not flow properly, or that the coin's too hard to manufacture.

Because the Mint is producing up to 750 coins a minute, any error is magnified. And the digital tools help make sure everything is spot on.

In the past, the Mint relied on panagraph machines known as Janviers that were first made in the 19th century and had no tolerance for mistakes. If one was made, it might be necessary that many more reductions of a design be done before arriving at a usable coin die. Today, though, the Mint uses CNCs (computer numerically controlled machines), systems that are automated, precise, and can cut more quickly than anything used in the past. That allows the Mint to focus on making sure the coins are made just the way they're supposed to be.

Congress controls much that the Mint does--such as new coin designs--and last year, Congress directed the Mint to move to the CNC system. That means that the last Janvier went out of service just a year ago, though the process of transitioning had been going on since about 2005. "We actually went from the 19th century to the 21st century in five years," Mercanti said.

Yet despite the romance of the old ways, he added that he has no nostalgia related to the change, which has "enabled us...to catapult so far forward."

Many new coins
Each year, the Mint has to produce a number of new coins and commemorative medals. For example, everyone knows about the 50-states quarters program, which just concluded last year. Now the Mint has embarked on a similar program in which it is producing America the Beautiful quarters--56 new coins over 11 years that celebrate the country's national treasures. The 2010 issues honor Arkansas' Hot Springs National Park, Yellowstone National Park, Yosemite National Park, Grand Canyon National Park, and Oregon's Mount Hood National Forest.

But there are also plenty of non-legal-tender issues: medals for the Army, 3-ounce silver or gold $5 pieces, clad 50 cent commemoratives, and many others. These are mandated by Congress, which has the power to legislate two new designs per year.

And while there are Mints in cities like San Francisco and West Point, N.Y., the actual circulating coins are made only in Philadelphia and Denver. And the lion's share are made here: fully 454 million coins came out of the Philadelphia Mint in June.

These days, that level of production means investing in the latest tools, and in recent years, the Mint has invested millions in new presses, CNC machines, and software. In addition to Illustrator and Photoshop, the Mint also relies on software like Freeform and Z Brush for 3D sculpting. The former works in conjunction with a haptic arm (see the video below) that allows designers to get physical feedback when digitally "sculpting," much as they would if they were using engraving tools on clay.

Here's how a brand new coin ends up in your pocket. First, Congress issues a law directing the Mint to make it--such as the America the Beautiful quarters. Then, Mint designers come up with an initial design that's vetted through the institution's legal department, ensuring there are no copyright problems.

Next, the design goes through two advisory committees, the Washington, D.C.-based Commission of Fine Arts, and the Citizens Coinage Advisory Committee. Once everyone there is onboard, the Secretary of the Treasury must sign off on the new design, and then it's on to sculpting, a process that can take from two weeks to months, depending on how many modifications must be made.

Production means master tooling, and five generations of reproductions from design to coin. First, designers create a model, then they produce a positive reduction hub--meaning one that's in the same orientation as the coin will be. Next up is a "reduction hub," which will be clean, ground to a specific form, and then put in a press with a soft seal and used to make a master die. Then, it's time for a "work hub," which is used to make the dies that will go in the presses and make the actual coins.

From that original master model, perhaps as many as 10 reduction hubs can be made, and from those, thousands of dies that will be used to make millions or even billions of coins. The hubs wear down over time, and the dies much, much faster, all because 400 to 500 tons of pressure are applied in the presses onto the steel dies.

The dies are made by scanning the plaster hubs, explained project manager Tony Petrella. He said he will use the scanner--just one such device is used in the production of all American coins--and take 30 or 40 pictures of each plaster hub, so that the software has as much data as possible before it's time to turn on the CNC and make the steel dies.

Once the data is handed off to the CNCs, those machines read the images created in the previous four generations and gradually cut the new steel dies.

This is not a fast process. It can take up to eight hours to cut a die for a penny, and up to 24 hours to make a 1-ounce silver coin. The cutting inside the CNC is done with a cutter that has a tip just six one-thousandths of an inch wide.

Finally, it's time for coin production.

On the production floor, there are countless coils of sheet metal, each coil corresponding to a specific denomination. The coils are fed into a machine, which punches out coin blanks that are then passed on to the annealing process--where they go through a furnace to soften the metal--and then are cleaned in a four-chemical wash. Then it's on to "upsetting," where a machine squeezes the blank, giving it an edge and making it better for striking by the press.

Finally, the blanks are sent to the stamping process, where one of 67 high-speed presses actually makes coins. In a typical day, the Mint here turns out 20 million coins, but it has a capacity as high as 50 million a day.

Two hundred thousand quarters
To make a quarter, a blank is hit with 61 tons of pressure. That happens a lot, as quarters pour out of the presses and eventually fill large bags that hold 200,000 of them, or $50,000 worth (see video below). Those bags are then closed up and shipped off to the Federal Reserve. The same process goes for dollars nickels, dimes, and pennies.

Walking around the floor of the stamping area, I come across the bin of dollar blanks. It's nearly full and must contain tens of thousands of them. Having overcome my Scrooge McDuck inclination, I put my hand inside and let a few slip between my fingers. It feels good, and makes a rich sound.

For the next few weeks, Geek Gestalt will be on Road Trip 2010. After driving more than 18,000 miles in the Rocky Mountains, the Pacific Northwest, the Southwest and the Southeast over the last four years, I'll be looking for the best in technology, science, military, nature, aviation and more throughout the American northeast. If you have a suggestion for someplace to visit, drop me a line. In the meantime, you can follow my progress on Twitter @GreeterDan and @RoadTrip and find the project on Facebook. And you can also test your knowledge of the U.S. and try to win a prize in the Road Trip Picture of the Day challenge.