Just curious, anybody know what the average lifespan of a die is (how many coins)? And if that varies much depending on the size and type of coin?
Depends. I'm not sure an "average" throughout the mint's history would mean much of anything. Perhaps you could narrow down the question to a certain era or even type?
Books is right , there's many variables to consider like what type of pressure was used the spacing of the dies . What metal was being struck and the size of the coin . I can tell you for the 1809 Bust half , 1,405,810 coins were struck using 8 obverse dies and 12 reverse dies . So it varied even for the same year and type of coin .
Listing all of the factors that play into die life would bore you . . . Coin design Planchet hardness Press type (mechanical vs. hydraulic) Die alloy Die hardness Die alignment Irregular strikes (clashing of dies, off center strikes, capped die strikes, etc) ZZzzz . . . As concerns averages, it would not be appropriate to assume die life is reasonably consistent from year-to-year, but it seems fair to assume that life might be somewhat consistent between dies of the same design in the same mint in the same year (same die alloy, annealing, sinking, heat treat, same presses, same annealing of blanks, same setup, etc.)
Relief, ie the raised section of the coin design is also a major factor. The US mint factors that now, look at recent nickels and cents - the dies have a longer life because relief is so low.
I considered relief as part of the coin design . . . and it's not only the relief, but how the design of one side relates to the design of the opposite side of the coin as well. Until Longacre, who was artful at this, had come along, it was generally not considered in the design of our coinage.
I imagine the speed at which coins are struck also matters. Don't we strike cents at about 700 per minute these days? Unfortunately, when you flatten the relief as much as has been done with modern nickles, the design just doesn't look so great (in my opinion).
"Planchet Size" should be at the top of the list followed by planchet hardness and then relief. In 1972 (The Ice Ages?) the Lincoln Cent Reverse dies produced the most coins per die with over 1.2 million strikes before retirement. (1.2 million coins on average) The Eisenhower Dollar produced far fewer strikes before retirement with only 100,000 per Obverse die. (100,000 coins on average) The above figures were pulled from the Authoritative Reference on Eisenhower Dollars and were provided by the US Mint as a request from Herbert Hicks in 1972. Since relief does play a part and coin relief has been lowered significantly since 1972, I expect that the above and below figures have increased dramatically. A Freedom of Information Act Request could be submitted for accurate numbers for today. Perhaps even for earlier years but it would be fairly costly since, from what I understand, the requestor picks up the tab for informational research.
According to what Peter Huber (Benchmarking Committee) said at the 2014 Mint Directors Conference, the average die life "covers a span ranging from 67,500 to a maximum of 1,929,927 coins." Not terribly helpful, hm? Christian
200,000 was the goal for a Morgan Dollar die, at least early on. I recall reading somewhere that the 1922 No D dies ended up striking something like three quarters of a million coins each to achieve that level of wear.
Cherrypicker's Guide 5th Edition Vol. II Average number of strikes for each... Lincoln Cent 1,400,000 Jeff. Nickel 200,000 (monticello design) Roos. Dime 300,000 (denver 400,000; phil. 230,000) Wash. Quarter 752,000 Statehood Quarter 275,000 Kennedy Half 160,000 Sacagawea Dollar 250,000 Presidential Dollars expected 150,000 to 200,000
The above figure begs the question, what is Denver doing to prolong die life whilst Philly cracks them up?
I don't know of any reason they couldn't. But if they did, it's possible that quality could suffer. Take just about any series of coins where examples were struck at multiple mints and usually one or the other will be known for having produced coins with the best strike. The reason for this is due to several things - strike pressure, die alignment, and die spacing. All 3 of these things are adjustable and if one or more is not set just right the quality of the coin will suffer. This may result in longer die life but just as with all things there are trade offs.
But they can align all three factors - look at the 1969-73 cents, they were struck with greater pressure than the other years - at all then three mints striking them.
Well, the fact that there were people in place with responsibility to adjust these parameters doesn't mean there were capable people in place, or that the local management fostered a winning workplace environment where everyone cared to do well. All you need to look at are the first few years of Morgan production from San Francisco, compared to later New Orleans work, to see what a difference people can make in the quality of the strike and the life of the dies.
