Die Making Process:
From 1792 till 1836, each die was hand engraved. The main design elements of the die were engraved in the Master Die. Inscriptions, dates or stars where applied to each working die. The die blanks were covered with a thin layer of transfer wax. The design of the die was placed over the die, and then rubbed with a smooth instrument. Then the engraver would cut the design. Because of this process, no two dies were exactly alike.
In 1836, the Philadelphia Mint installed a French Portrait Lathe. The use of this lathe eliminated the need of the engraver to cut the Master Die. A hard model of the die was made and then the lathe would rotate clockwise and cut the design into the Master Hub. Once completed, the Master Hub was used to produce the Master Dies. This lathe was used until 1868.
In 1868, the Hill Reducing Lathe was installed. This lathe allowed the model to be larger than the coin it would later produce. This process would improve the quality of the coins. The Hill Reducing Lathe was used until 1907.
In 1907, the Janvier Lather was installed and is still in use today. During this die making process, the model could be much larger than the coin. The first two digits of the date would no longer need to be punched into the Working Die. This now would be included in the model, called a Galvano.
The Janvier Reducing Lathe would track the Galvano and cut the images into the Master Die. The Janvier Reducing Lathe turned clockwise very slowly. It could take days to cut a Master Hub.
Now the Master Hub, with the first two numbers of the date, could be used for years.
In the mid 1980’s, the Galvano was produce with all four digits of the date. A new Master Hub has been produced each year since.
During the hubbing process, the Master Hub was impressed on a blank die. This is done with a slow hydraulic pressure of about 100 tons. It would take several hubbings to place the design of the Master Hub on the Master Die. After each hubbing, the Master Die would be placed in an annealing furnace and heated to cherry red. The Master Die was then removed and allowed to cool to room temperature. This softened the Master Die.
Then the process would begin again. It was normal for three or four hubbings to occur on small coinage. It was not uncommon for the Morgan dollar to require ten or twelve hubbings before the Master Die was completed.
A few Master Dies would be produced and these Master Dies would then be used to produce many Working Hubs. The hubbing process would be the same when producing the Working Hubs.
Each Working Hub would produce hundreds of Working Dies. Now remember that the hubbing process is repeated each time a new Working Die is created.
In the early 1980’s, the Mint started using a new “One Squeeze” process for Lincoln cents. In this process, the Master Hub is still produced from the Galvano. But this is where the process stops. The Master Hub is then used in a new “One Squeeze” Hubbing machine. The Master Hub is used to produce the Working Die.
The “One Squeeze” Hubbing machine uses hundreds of tons of hydraulic press to squeeze the design elements of the Master Hub into the Working Die. This is done with only one hubbing.
A few years later the Philadelphia Mint started producing nickel and dimes with this “One Squeeze” process. In the early 1990’s, quarters, half dollars and SBA dollars were converted to the “One Squeeze” process.
It was during my tour that I learned that the “One Squeeze” process does not always work and that rarely, a second hubbing is needed. I also learned that only one Working Die is produced at a time. I also noticed that the old hubbing machine is still installed and ready for use if needed.
This new process has saved the Mint time and money in the production of Working Dies.
Now lets examine the non-automated side of the coinage production. Many new minting processes were learned during this part of the tour. Some I have never seen in print before.
Non-Automated side of the Mint:
The planchets were fed into the coinage presses by large hopper at the top of the coinage presses. The machines were completely surrounded by shields, to protect the workers.
The coins came out of each coinage press onto a revolving wheel that moved the coins into a holding bin on the side of the machine. This holding bin was angled down toward the floor. The operator would pick up a few coins and examine them for defects with a three-power loop. If there were no defects, he would release the coins from the holding bin and they would proceed down the holding bin and drop about three feet into a large metal scoop on the floor.
This metal scoop was higher in the back with no height in the front. The sides of the scoop went up at an angle equal to the distance between the front and the back. (The height of the sides increased as they moved toward the back of the scoop. On the back, outside of the scoop was a big o-ring. The scoop looks to hold between 100,000 and 150,000 coins.
An overhead conveyer would move across the ceiling and stop above the scoop on the floor. A hook would be lowered to the ring on the scoop. A mint employee would place the hook into the o-ring on the back of the scoop. The conveyor would raise the scoop and move it over to a tank. Scoops from several coinage presses are emptied into a tank before the tank is loaded onto a “Sizer” stand. These coins are then released into a “Sizer” that also has a “Riddling screen” attached.
After going through the “Sizer” and the “Riddling screen”, the coins fall into another tank. At this point, the coins have been well mixed. No longer are the coins in any type of order. This tank is then taken to the counting and bagging area by a fork truck.
The next section of the Mint is what I call the “Hybrid” section. It is not really automated and it can not be called non-automated. This part of the Philadelphia Mint has the coins feed into the “Hopper” at the top of the coinage presses by a conveyor belt. These coinage presses are also surrounded by shields to protect the workers.
The coins came out of each coinage press onto a revolving wheel that moved the coins into a holding bin on the side of the machine. This holding bin was angled down toward the floor. The worker would inspect a hand full of coins with a 3 power loupe.
If the coins had no imperfections, he would release the coins from the holding bin. The coins would travel down and drop into a tank. These tanks looked to hold between 800,000 and 900,000 coins.
On a regular schedule, fork lifts would come around and pick up the tanks and take them over to the “Riddler and Sizer”. Several tanks could be emptied at the same time. This again would mix the coins from several coinage presses.
The coins would travel along the “Riddler and Sizer” and empty into another tank at the end of this process. This tank would then be taken to the counting and bagging area by a fork lift.
Next issue we will cover the automated side of the Mint, the counting and bagging operations and coin storage.
Have a question, need an answer, drop me a line. Frank M. Zapushek PO Box 1993, Bloomington, IL. 61702. mrz@bakercoins.net Your question might be my next article. No charge for authentication or questions.