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The US Mint explains it's incused lettering process.

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Has anyone seen this? Maybe it will enlighten a few more of those people buying these off ebay that they aren't errors.


Edge-Incused Inscriptions


The edge-incused inscriptions found on Presidential $1 Coins include the year of minting or issuance, "E Pluribus Unum," "In God We Trust" and the mint mark. However, there are two processes for producing the edge-incused lettering and each produces a different result.


Circulating and "Uncirculated" Quality Coin Edge-Incused Lettering Process


Due to the minting process used on the circulating and "uncirculated" quality coins, the edge-incused inscription positions will vary with each coin.


The Presidential $1 Coins are inscribed on the edge without regard to their "heads" or "tails" orientation. In addition, the location of the inscriptions around the circumference of the coin with relation to the obverse and reverse designs will vary as well. This is because the United States Mint incuses these inscriptions on the edge of each coin at the second step of a two-step coining process.


In the first step, the blanks are fed into a coining machine which strikes the obverse and reverse designs onto the coins, and dispenses the coins into a large bin. In the second step, the bin is transported to the edge-incusing machine, into which the coins are fed at random, without regard to their "heads" or "tails" orientation.


Therefore, statistically, approximately one-half of the coins produced will have edge-lettering oriented toward the "heads" side (obverse), and approximately one-half of the coins will have the edge-incused inscriptions oriented toward the "tails" side (reverse).


Proof Coin Edge-Incused Lettering Process


The minting process used to manufacture the Presidential $1 Proof Coins is a one-step coining process that allows the edge lettering to appear in a consistent location on every proof coin. Using a three-piece collar, the edge lettering on the proof coins is incused in the edge of the coin at the same time that the obverse and reverse design are being struck onto the blank planchet.


This method produces edge-incused lettering that will always appear right side up when the coin is showing its "heads" side. Furthermore, the location of the lettering will always be in the same location on the circumference of the coin with relation to the obverse and reverse designs. In addition, the proof coins will each bear a faint demarcation line where the three segments that make up the edge lettering collar are joined.


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Nothing new, but its a good review. BTW, why can't they use the three piece collar for business strikes, like they do the proofs? Seems like it would end a lot of these missing lettering errors.

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Rumor has it that the mint has invested lots of money to make the BS coins a one step process like the proofs. I don't know if they're using a 3 pc collar like the proofs or some other system but the idea is to get rid of the edge lettering errors which they don't find nearly as interesting as numismatists do. I haven't been able to find anything about when this new equipment will be in use (Monroe?) or what exactly it is. --Jerry

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It has to do with the speed at which they strike the coins. The plain edge collar is a simple device just a hole in a heavy disk of metal. Now this hole is offset from the center of the disk and the disk rotates around its center to bring the planchet in between the dies and then out again after the coin is struck. To accommodate the speed of the press the collar disk has several holes in it that are brought between the dies in quick succession. If the disk has three holes in it the disk has to rotate at four times per second, if it has four holes it rotates three times per second.


Now if you are trying to use a lettered collar each of these holes instead of being a hole in a solid piece of metal has to have the metal split into three pieces at each location and there has to be the mechanisms there to open and close those pieces and all those parts and mechanisms somehow have to be driven, yet still be able to rotate around with the disk. It would just be a mechanical nightmare.


The other option would be to just use a single hole collar that doesn't rotate like they do for the proofs. But while with the proof this collar assembly has to open and close around once every second or two, on the business strike it has to be able to open and close twelve to thirteen times per second plus you have to have some kind of feed finger assembly to deliver the planchets to the striking chamber, which means that the dies have to be spaced even further apart to make room for the feed fingers, which means that the press has to run even faster because now the dies have to travel twice as far during each stroke. That means that the dies spend even less time accomplishing the actual "squeezing and forming" part of the strike. Since there is less time to actually bring up the strike, the relief will have to be lowered even further than it already is. Probably lowered considerably.


If you want to keep from lowering the relief then you have to slow down the press and increase the number of presses used to create the coins. That means more equipment, more workers, and considerably more space needed to produce the same number of coins.

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Great explanation. Sounds like you actually know the expected production rates from each machine. None of the options you discuss are consistent with the "keep it simple" design principle that is so key to error free production. Thinking about it they may just create new errors with this new equipment, especially if they rush it into production.


If I were in charge or quality at the mint I would vote for more machines working slower. The bean counters would be pushing for less machines working faster....



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