How Worn Can A Die Be and Still Strike MS Coins?

What limit is that?

 

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Intolerable, to say the least! Wear to a working die should be penalized responsibly.

 

This is why I use the term “cartwheel luster” independently of “luster”.

 

VEDS coins are more like you describe Proofs, with narrow/sharply focused luster. As with Proofs, the luster is there for a different reason than it is for late die states. On Proofs and VEDS coins, the die surface itself is still smooth, so the surface of the struck coin is smooth, but the coin metal has fine structures of metal flow on the surface that produce a subtle luster. On LDS coins, the cumulative metal flow from millions of strikes wears these metal flow patterns into the die surface. So in addition to the fine metal flow structures in the metal itself, the die imparts its worn metal flow patterns onto the surface of the coin. This creates a more pronounced luster in LDS coins than is seen in Proofs or VEDS.

 

Like you said earlier, and even earlier before that when this thread went around the first time, we'll just have to agree to disagree. I think though that you are a minority of 1 in your opinion, so eventually you may want to rethink the topic.

 

You are not wrong, but to be more precise, the planchet metal flows toward the regions of lower pressure, which tend to be the raised devices, and the rim. You can see the effects of this movement on the edges of all devices on an LDS coin. When a coin is VEDS, the edges of devices are sharp where they meet the field, but on LDS these same edges are rounded and show the effects of metal flow wear. At the very outer edge of the coin, the metal indeed flows outward, since it is the lowest pressure way to go. This quickly creates strong wear to the periphery of the die. There are also areas of the die where the flow is "ambiguous". On the Lincoln Wheat Cent, the areas in the field in front of the face, and in a curved region behind the head. Same areas of the Jefferson Nickel show this flow ambiguity. This is the highest pressure region during the strike, where metal flows outward in all directions. Metal inside those regions flows inward toward the bust, while metal outside those regions flows outward toward the rim. Within the ambiguous flow regions, the wear patterns can be "interesting".

 

You almost had me until you said this...

 

I am torn on this subject. It seems that the metal definatly has to flow into the devices I think it thoroughly depends n if the rim extends past the devices. the way a die moves is individual depending on the way it's made.

 

(Not divoid from the coefficient of thermal expansion)

I am interested in what you guys are talking about in this thread. In my mind I have read to understand the following:
A Planchet expands radically when struck creating radial flow lines as it [fills] the collar. A planchet being smaller to start with would drag to conform itself outward against the surface of the die. Forming tiny grooves over it's course the die will then transfer these to subsequent coins. As the metal [planchet] is flowing in whatever direction it takes to get to where it needs to be the effects can differ near or around the devices. It is true then as the die wears it will impart those micrscopic lines that catch the light to form it's particular lustrous appearance. So wouldn't it be safe to say since " it's" limited ..that the metal goes with the flow?

 

@GDJMSP okay I took a handful, about 50 of nice clean Gem BU Lincoln cents from the sixties and looked at them under the trusty Swift stereoscope at 10x low and behold I see flow lines in most of the cents. After closer inspection at 45x it’s a hole other world but it’s clear to me that your theory has merit the metal appears to flow to the middle in most of the coins inspected. The rim being some bone of contention but it’s clear that the material in the finished coin rim came from the upset that has been put in the planchet. If anything there is excess material that has to flow away from the rim at the time the coin is struck and it kinda looks that way in some of the coins I looked at. All I know is this all takes place at high speed and we can never actually know how it happens we just see the end results.
I agree with you Doug.
Reed

 

This will be a constant reminder to not post while drinking Tequila.

 

What a beautiful coin!

I think you might be making the assumption that the metal which fills the devices comes from the surface of the coin, moving against the die as it is forced into the raised areas. However, this is simply not the case. Only a small amount of metal actually moves across the die surface. The vast, vast majority of the metal comes from the bulk of the planchet, well below the surface. The only places where significant metal moves to fill the raised devices is on the device edges. Because of the general metal flow (from below) to fill a large device such as a bust, metal on the surface is "pulled along" near the device, but in general this movement does not extend a great distance beyond the device. I believe you can see where the flow changes from "inward" to "outward" in this coin very clearly. It is those dark areas in front of the face and behind the head. I think the dark area at the forehead is probably die polishing remnants but it may be another of these "ambiguous flow" regions as well.

It's easy to prove this is incorrect simply by looking at what happens with a broadstrike. Broadstrikes cause the metal to flow outward toward the rims, making the coin larger than normal. In a normal strike the collar constrains this flow, but the general direction of the forces is still the same. Indeed the central devices are still filled due to metal moving from below to fill the voids in the die, and I would expect some inward movement of metal at the die surface near these voids, but farther out toward the rim the direction of the forces changes, and the movement is outward.

 

There is no magic in broadstrikes that limits the outward forces just to them. The collar is there to keep the metal from flowing outward. No collar, metal flows out. This means there is lots of outward force against the collar, caused by the die pushing metal outwards.

Fully agree with this

It's not a belief, it's simple physics of how the metal flows. I agree with you that metal near the center of a coin, with a significant raised device such as a bust, will flow inward to fill the large void in the die. But I absolutely, adamantly, vehemently, disagree that the flow is outward across the whole die surface. It's just not so.

I like to look at extreme cases to see if my assumptions are correct. The broadstrike example is one of these cases. But an even more extreme case would be completely blank dies, with no features. What would you say if there was no design at all on the coin? The correct answer is that in this case, the flow of metal would be 100% outward radially from the center of the die. This extreme case illustrates that the general flow direction is outward. Adding voids to the die will locally disturb this trend, but only locally, not in general, and the general outward flow will be restored as you get farther away from this local disturbance