I recently ran into a couple copper planchets that were never struck. They weigh 3.10 and 3.08 grams so I know these are pre-82 planchets. They already have a rim around the edge, but the strange thing is they are thinner than a finished Lincoln cent. Whether I put them on the table or hold them together and check through the loupe, the thickness is definitely different. Are they normally like this until struck and then the rim gets thicker or are these planchets for something other than a Lincoln cent? They are the same diameter as a cent piece with the same weight, which led me to believe they were unstruck Lincolns.
Yes, all planchets are thinner than the finished coins. Of course that depends on where you measure the coins. If you measure a coin field to opposite field, then the coin is much thinner than the planchet. The fields are where the metal comes from that fills the devices, rim, and edge of the coin. But if you measure a coin device to opposite device, or on the rim, then the coin is thicker than the planchets.
There's nothing you can do to a planchet of a given size to make it thinner. Two things though; The edge of a type 2 planchet is upset by rolling it to push up some metal around it to help form the rim so a type 2 planchet can, at least in theory, end up thinner as a struck coin (they rarely do in practice). Also the planchet is fairly soft metal and it is work hardened in the strike so the volume actually does decrease slightly even though the thickness increases. Rims are put on coins so they can be counted in stacks even though almost no one does any longer.
Thanks for the great info. So basically when the coin gets stamped, it pushes metal into the fields, making it thicker in some areas since the metal has nowhere to go. Makes sense.
And the planchets are also slightly smaller in diameter than the finished coins. If they were the same size they would not drop easily into the coining chamber and there would be a lot more striking errors (off-centers, broadstrikes, tilted partial collar etc).
Not true Sam. A finished coin is always thinner in the fields than the unstruck planchet was. The metal the fills the devices and the rim has to come from someplace, and it comes from the the fields. Thus making the fields thinner than they were. The reason they use an upset mill on type 1 planchets to make them type 2 planchets is because striking pressure would have to be much higher if they did not. Otherwise the rims would not form correctly. And if pressure was higher the dies would not last. As everybody knows, when a coin is struck the metal flows. And when the metal flows the metal becomes thinner. The reason the metal flows is because it is literally squeezed, squished, between the 2 dies.
