2012 Jefferson Nickels: Machine Doubling Identification, Attempt #2.

I have been doing a lot of reading on Machine Doubling. My summary, some conclusions, and then questions.

I think we all agree that this is not a real doubled die example. (Actually, I don't think anyone ever proposed that, but I am being 100% clear). The question here is: what specific kind of Machine Doubling happened to this coin? We have correctly proportioned devices accompanied by a thin duplicate shelf in a single uniform direction.

This does not appear to be Die Deterioration Doubling. DDD examples on Error-ref.com look soft, rounded, and mushy. Our specimen is sharp, flat, shelf-like. The overall obverse coin strike looks pretty clear.

Error-ref.com lists three sub-types of Machine Doubling during striking. Rim-restricted doubling is not relevant here. Slide doubling, which smears the design as the die drags across the newly struck coin, also doesn't seem to be a candidate. The ER description of Push Doubling matches a lot of Coop's examples in the #1-30 range. But that's the complete Machine Doubling entry at Error-ref.com. ER also lists flat field doubling for twice struck proofs (not relevant here), and ejection doubling, which produces effects like Sacagawea's extra eyes (also not relevant here).

I note that visually the effect here is very similar to flat field doubling on proof coins, but that's obviously excluded from the possibilities.

The problem I have with a push doubling conclusion is that the devices here do not seem to be cut into a shelf by a subtractive process. Everything is basically the correct size and outline, with a thin duplicate shelf underneath. Numidian has showed that quite well with his overlays.

Approaching #100 in the Coop slide deck, we encounter "die movement doubling". It's a term I had not heard before on any site like ERef. The device appears correctly struck, but a shelf edge has been "pushed". That looks pretty darn close to my nickel.

However, the term "die movement doubling" produces no results on Google. Obviously it's a phenomenon separate from the subtractive Push Doubling process. Is there a formal term for DMD? What is the cause? It doesn't seem like DMD can have the same cause as PD because PD relies on cutting some of the device metal into a shelf, which thins the devices. Nor does DMD seem that it can be caused by Slide Doubling because that process smears the metal.

So what is Die Movement Doubling, what specifically causes that, and is that what happened on this nickel?

In re-examining the nickel vs. the reference coin, I am now noticing that the strike seems shallower and less distinct than the second coin. I had initially assumed that was circulation wear, but maybe that is a sign of some Die Deterioration or polishing?

It's a fair question.

I am an engineer. The science of things matters to me. When I do a root-cause analysis, I get to a satisfactory explanation or I keep digging. I have very much enjoyed this discussion so far, even if the coin is worthless.

I think people here give an answer of Machine Doubling (really meaning push doubling) far too easily. If the cause does not correctly explain the effect, then the scientific method requires further investigation. The term Machine Doubling itself seems to encompass a large number of common and uncommon scenarios that are not identical in formation or result. If we cannot point to a specific type of error from a specific cause, then that is guessing, not knowing with confidence.

Also, the doubling question seems to arrive often from newcomers to this site. True die doubling is probably 1% of those cases. The various forms of MD/DDD and other manufacturing flaws are 99% of those cases. So all we have to do is guess Machine Doubling every single time, and we are likely to be correct with a 99% record. If we are looking for a valuable and rare 1%, then that is not a very useful strategy. I could throw out every tiny transparent mineral in my prospecting pan, but that guarantees I will never find a diamond. I would, however, be correct 99.99% of the time. Does that represent a mastery of diamond prospecting, or merely describe a basic grasp of probability? It seems quite possible to be 99.99% correct and achieve a result of $0.

It is also worth asking the question in reverse. If I am sure that a coin has true die doubling, then I must first rule out worthless forms of doubling. Some of the legitimate forms of doubling like distended hub doubling seem to look very much like MD/DDD. How can I be trusted to identify a diamond if I cannot immediately dismiss quartz, glass, and other lookalike minerals? This seems especially important for doubled die coins, because the odds of finding one are tiny. A collector seems much more likely to purchase such a coin. You don't buy a Rolex if you can't identify a Rolex. I guess you can buy a Rolex from a certified dealer, but then you're just "buying the slab, not the coin".

If I had found a different type of interesting error in a roll of nickels, I would be doing a deep dive on that subject instead of this one. =)

All good points, Brandmeister. I went through the same thought processes back when I was roll searching nickels, which is the denomination I've searched most. I think you've reached a sort of wall in that few have pressed onward to the details you seek.

A bit of knowledge that you may not have encountered yet is that coinage dies are slightly convex. Consequently, when a coin is struck and the dies begin to separate, different parts of the new coin are released from die contact at slightly different times. That helps explain why we so often see Machine Doubling on only part of a coin.

I designed and built metal stamping machinery, and can say that.determining the cause of a product defect can be challenging. To root out the cause of each form of doubling might require a coin press with which one can run experiments. The mint's machinists likely know many of the details you seek, but eventually even they probably hit a knowledge wall.

Okay, my bad. I thought we were deciding among DDD, die abrasion, or some kind of " Machine Doubling".

The problem I have with push doubling is that it does not explain 1. why the devices are full size, and 2. where the extra metal came from to form the shelf. You laid that out pretty well with your illustrations.

I, too, am quite curious to hear Coop's explanation for Die Movement Doubling. I think the reason for the term is clear—it doesn't seem to follow the rules for push doubling, and thus quite likely has a different cause.

We see Machine Doubling near the outer edges most often because if the coin rotates relative to the die, the coin's outer edge moves the largest physical distance.

Die Movement Doubling sounds like a loose die is rotating or shifting rather than the newly struck coin.

Besides the ones we've discussed, there are other factors that will influence Machine Doubling. For example, if the dies are not exactly parallel to each other, either due to improper installation or wear, when the dies separate after striking the coin, they will lift off first on one edge, and last at the edge 180 degrees away. If the coin rotates during that period, anomalies will happen near one edge and not the other. I imagine the design itself can also influence where anomalies are most likely to occur.

If you are seriously into such details, you could probably study and write a paper or book that would be welcomed by the hobby. I would be interested in your findings, but I don't know how many others would. This is esoteric stuff.

Agree there is a subjective element to what makes a coin valuable, but there is also rarity. A true doubled die is created by a specific die pair until the Mint pulls that die from service, and for most coins that makes a doubled die example a small percentage of the total mintage.. By comparison, Machine Doubling is common. There may be certain modern years and mints for which it is uncommon, but AFAIK no one bothers to survey that.

Even though I don't find most Machine Doubling attractive, I set aside the extreme examples due to their curiosity. I'd bet a complete a set of machine doubled Kennedy halves would garner a respectable premium on ebay, even with a clear description they are not doubled dies. The bottom line remains collect what interests you, regardless of value to others.