Just curious, why is MD considered worthless while other doubling isn't? Aren't they both mint errors? Maybe I don't understand what a mint error is.
True doubling occurs during die manufacturing. There are processes and inspections to make sure that defective products don't make it to production (although some still do) MD is due caused by a normal die moving slightly during striking. The mint is a high speed, high volume operation where time = $$ (both figuratively and literally). Nuts and bolts can loosen or break, changeovers may not be tightened to spec, Wear and tear, etc. Thousands or tens of thousands may be struck before a technician notices a problem. Go through a roll or two and your bound to find some MD or DDD coins. When you can get as many as you want for face value, why pay extra.
Because true doubling is on the die and can strike thousands of planchets, it is a variety not an error. https://coins.thefuntimesguide.com/us-coin-errors-and-varieties/
So it happens during the minting process, and yet it still isn't called a mint error? How does that work?
It is very common so it doesn't add any additional value. There's nothing wrong with collecting them, just don't get upset if others don't share your enthusiasm. IMO, there is a big difference between collecting something you find interesting, and insisting that it should be called an error to add monetary value. From Wexler's Doubled die site https://www.doubleddie.com/144822.html As we indicated before, this form of doubling is extremely common with numerous examples being produced on all denominations every year. Most serious doubled die collectors view this type of doubling as a form of damage to the coin rather than a collectible form of doubling. We are not saying that you cannot collect this form of doubling, if you are interested in it. Rather, we are saying that you should know the difference between the two forms of doubling and label them properly. Knowing that mechanical doubling is an extremely common form of doubling you also need to be very realistic about any values that are assigned to coins with this common form of doubling. You can also check out this link http://www.error-ref.com/?s=Mechanical+doubling
@Wagnasty87 I have to assume, since you've been a member here for over three years, that you are a casual coin collector. As such, I can see why you would ask the question you did. The links, along with many others, would help educate you to the many different types of "doubling" so keep asking your questions, but do some reading and a little research so you become more experienced. Just a suggestion if you are interested in continuing collecting.
No, that's not what I'm asking. I don't care about collecting them or their value. I'm wanting to know, since it's done at the mint, why isn't it considered a mint error?
An error in general terms is something that occurs once, broadstrike, capped die etc. Machine doubling can happen to thousands of coins until it is noticed and the loose die tightened up. Because of the amount of times it happens to all types of coins and denominations, it simply is dismissed as an error even though, in strictly technical terms, it is one.
Machine doubling is a mint error, and anyone saying it isn't is missing the nuances of the term. Yes it's an error, it's just a "NAV" (No Added Value) error. Collectors do not find Machine doubling, and a whole host of other occurrences at the mint that would be technically and documentally "mint errors", as valued, and they won't pay a premium to add them to their collection, Most just will dismiss it as "not an error" rather than explain it, it is a mint error, it's just not going to get you any money above the value of the coin is all. There are even true doubled dies, that occurred on a master die and as so got passed to the working hubs, and then the working dies. The majority of that years mintage was struck with the doubling. they are so common that they fall into the "NAV" category also. The 1944 Washington quarter is like this, for all 3 mints of that year. doubled die under the nostril and under the ear of george washington on the obverse. There's also another on the 1972 Lincoln cent. there's plenty of "mint errors" that are listed in error reference catalogs that nobody finds value to them in the hobby and it doesn't add value to the price of a coin. machine Doubling is one of them. A doubled die, should be on the working die, and every coin struck with that die, has the same exact doubling. if it's one of the working hubs, it's going to be on more of the dies, and if it's on the master die, it's going to be on all the working hubs, and all the working dies. collectors like them repeatable with examples, like on a die run, or even dies made from one working hub where it would be more common than just a single working die. but when it becomes too much, then it just becomes the way they made coins that year and there's no added value to the variety. LOL With machine doubling, the die is loose or not set quite right, or it bounces on the strike, the cause varies, but it isn't on the die itself, it will vary from coin to coin on the appearance on the coins. on a "doubled die" (literally meaning the doubling is on the die), it's going to look the same for every coin struck with that die until it's retired.
Yeah, machine doubling. Yeah I know it's not far! IMHO it's still an error and should be counted as one. Besides, the mint did it, not post mint damage!