The blanks are now planchets and are ready to be struck into coins on the Mint's coining presses.
A new prototype inspection system underwent testing at the Denver Mint in 1996. Planchets are carried along a conveyor belt beneath electronic sensors that reject substandard pieces. Both sides of the planchets are examined. A Coin World staff member examining planchets rejected by the prototype was amazed at how well the machine caught even minor imperfections.
Coining presses are designed for any denomination of coin. Dies and collars are interchangeable and striking pressures are adjustable for the various denominations and metals. A circular piece of hardened steel forms the collar, which acts as the wall of the coining chamber, and one die forms the bottom. The dies impress the various designs and devices on the obverse andreverse for the coin while the collar forms the edge of the coin, flat and smooth on cents and 5-cent coins and reeded on the larger denominations. The collar, which is five-thousandths of an inch larger in diameter than the dies, is mounted on springs which allow slight vertical movement.
Generally, the reverse die is the lower (or anvil) die while the obverse die is the upper (or hammer) die; however, there are exceptions, and on some presses, the dies are mounted horizontally so that they move parallel to the floor. Still, the terms anvil die and hammer die are appropriate.
Planchets are fed by gravity from a basin attached to the press through a cylindrical tube. This tube stacks 20 or so planchets. From this stack the bottom planchet is fed into the press by one of several feed devices.
One device is called the feed fingers: two parallel pieces of metal joined in such a way that they can open and close; on one end of the two pieces is a covered recessed slot and in the center is a hole. A second device is a dial feeder: a circular piece slotted with holes which transport the planchets to the coining chamber and then transport the newly struck coin from the dies.
No matter which feed device is used, the coining process is the same. The anvil die at this point is stationary. As the hammer die moves toward the anvil die it impresses the designs of both sides into the planchet and then completes its cycle by moving upward to its original position. On presses using the dial feeder, the dial remains stationary so that the hole transporting the planchet remains centered over the anvil die, with the hammer die passing through the hole to strike the coin. Now the anvil die starts to move above the collar, actuated by an eccentric cam, raising the struck coin out of the coining chamber. Depending on the feeder system used, one of two things happens.
As the anvil die moves, about the same time the feeder fingers, in a closed position, start to move forward with a planchet lying in the center hole. At this time the anvil die reaches the top of its cycle, the recessed slot (ejection slot) slides over the struck coin, and pushes the coin away from the coining chamber. The feed fingers have completed their forward movement and now the center hole is moving towards the coining chamber. Having imparted movement to the struck coin, that coin continues onward until it hits a shield which deflects it into the struck coin hopper. The feed fingers open, allowing the planchet to fall into the coining chamber. Then the feed fingers reverse direction to return to their original position.
On presses using a dial feeder, the struck coin is pushed back up into the hole that had carried the planchet; the dial rotates, moving the coin away from the coining chamber while the next hole drops a new planchet onto the lower die. The cam action now causes the lower die to move to its stationary position.
Presses fed by dial feeders have sensors that automatically stop the press if a planchet is mispositioned, of the wrong size or incomplete, or is completely missing. The Denver Mint especially has good use of this feature to largely eliminate many of theerror coins that entice collectors.