Marvel of Engineering, Part 1

The size of a single U.S. cent must be accurate within 0.08mm, the width of a strand of human hair, and its weight within 0.13g. This precision must be repeated billions of times a year. At full capacity, the U.S. Mint is capable of minting over 1,630 coins per second, allowing it to theoretically mint around 150 million coins per day! This degree of precision, along with sheer volume, makes modern coinage one of humanity’s most astounding mass manufacturing achievements. It took centuries to reach this level of perfection. 

Hammered Coins

Let’s travel back in time to a thousand years ago. Imagine a noisy workshop filled with smoke. Workers with tongs and hammers are milling around. A place like this is where the earliest coins were created. Each coin was handcrafted using metal from a nearby mine. The metal was first sent to be refined and purified, then molded into ingots. Workers hammered the ingots into thin strips, then cut the strips into rough blanks, called flans. Workers heated up the blanks, which softened the metal and allowed the design to be fully struck into the coin. A lower die was placed on the anvil while the higher die was held by hand or with tongs, and a hammer blow transferred the design to both sides at once. 

Cast Coins

Across the globe, the Chinese created coins by casting them with molds made out of bronze. Craftsmen carved out the exact image that was desired, then poured melted metal into the molds until it cooled. Using a tree metaphor helps explain this process—“branches” in the mold allowed the metal to flow into nearby crevices, resulting in dozens of coins per mold. Workers broke up the coins and painstakingly filed them down. An ancient Chinese cash coin (aka qian) is a famous example of a cast coin. Casting allowed for quicker production and a more uniform look. However, the weight could vary and molds often broke down. 

Ancient Roman and Greek coins, for example, were not perfectly round or of the same thickness. Off-center images, flat spots, clipped edges, and noticeable weight differences were commonplace. Regardless, this was a huge leap in the production process. Coins like these allowed the ancient economy to flourish and were trusted by merchants and traders. They could be easily transported and exchanged, providing a better system than bartering. However, many problems remained. One of the major hiccups was figuring out a way to consistently mass-produce coins at scale. Still, with this system, the Romans were able to mint an estimated 20 billion coins. 

Screw Press

This system was used until the early Renaissance, when inventors began to develop more mechanized solutions. By the 1500s, European mints utilized a new machine—the screw press—which allowed for greater pressure and more consistency. A screw press had a vertical threaded shaft with a heavy crossbar on top. Workers turned the crossbar, driving the screw downward. One die was located on the bottom while the other was on the screw, and the coin was placed in the center. In later years, the screw press used water and animal power. 

One of the main benefits of the screw press was mechanical advantage, which allowed for a strong, more consistent strike and thickness. Some screw presses also utilized a collar, which held the blank in place before being struck and produced a more uniform diameter.

Rolling Mill

Another invention introduced during this time was a rolling mill, which allowed mints to turn their ingots and bars into long and relatively even strips, resulting in greater quality control and more consistent weights. Early on, blanks were cut by hand with something similar to a shear. This slowly evolved into simple blanking presses. For the first time, minters were able to control the weight and thickness of the coin by using rolling mills and blanking presses, instead of guessing with a hammer and chisel. 

All these small changes led to huge improvements in quality and quantity, which is apparent when comparing medieval coins with ancient coins. Machines that utilized mechanical advantages allowed for more precise control, along with mass production. However, there were still major hurdles. Most of the process was human-powered.

Steam Power

By the 1700s, both science and technology were making great leaps, and a little-known Baptist preacher and local blacksmith was about to make his mark in history. Englishman Thomas Newcomen was experimenting with ways to pump water out of mines. His work led to the creation of one of the most important inventions ever. In 1712 he created what he called the “atmospheric engine,” an early model of what is now known as the steam engine. The steam engine allowed for faster transportation and the establishment of large factories. It also contributed to the rise of large urban centers. 

Additionally, the steam engine provided power for mints. By the late 19th century, most mints used some form of a steam press. A notable example is Matthew Boulton’s Soho Mint, which was one of the earliest mints to adopt steam-powered coin presses to strike coins. It was capable of minting 70-85 coins per minute, which was a major breakthrough at that time. Capable of delivering far greater energy at a speed impossible for humans, steam-powered presses quickly became commonplace in other mints, and manual presses were phased out in just decades. 

However, the biggest improvements would occur in the following centuries. I’ll cover these advancements in my next article, to be published in April.