"What Caused spiral marks on a coin?"
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A poster on the PCGS boards asked "What Caused these spiral marks on a coin?" and showed the following photo of a 1990-D Kennedy half dollar.

 

1990d1.JPG

 

The arcs are uniform in size, occur throughout the coin including relief and tops of letters, and seem to have a common center of rotation. In these respects they resemble machining grooves made during trimming of rotating bar stock.

 

The consensus was that these are so-called "lathe lines" made when the end of die stock was machined before the design was impressed. Sounds reasonable; however....consider another idea.

 

Multiple impressions from the hub were required to create a complete working die.

As these impressions were made, all machining marks were obliterated beginning with the center and moving outward. No fine concentric lines would remain on the portrait or any other part of the finished die.

 

Notice that the photo shows concentric arcs in both the field and relief. This is not possible using pressure transfer methods. (Assuming the hub was not defective....but then we would expect to see a lot of coins with this defect.)

 

The likely cause comes from post-transfer finishing of the die.

Following its final blow from the hub, the soft steel die required cleanup. This was and remains completely normal. This was done either manually by an engraver using small tools and emery sticks, or mechanically using a rotating lap charged with abrasive. The purpose was to smooth the inevitable remaining defects. If the abrasive was too coarse or contaminated with coarse particles, they would leave concentric arcs over the entire surface. Something like this should have been caught on inspection. (At certain times, cleanup might have been done after hardening of the die – we simply do not have enough U.S. Mint practices information to make a definitive statement. Mint machinists did not routinely interact with commercial workers in the same line of business; the mints thought of themselves as holders of “secure information” of critical importance and did little writing about techniques.)

 

Most occurrences of this defect show a center point of rotation of the abrasive lap. That means the lap and die were probably in a fixed position – probably mounted in the chuck of a horizontal machining lathe. Some coins have concentric arcs with different (multiple) centers of rotation. These were likely done with a small manual lapping tool much like a tiny disk sander.

 

This phenomenon is found on circulation coins and proofs from the pre-WW-II period, and commemorative halves, among other coins.

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Here is simplified version of how lines like this get on a die. Think of it like this. You place a die in vice, and then you polish it with an abrasive brush that is mounted on an electric drill. The circular motion of the drill creates the circular lines which are into the die. They show up as raised lines on the finished coin.

 

I've gotten more than my share of polishing lines on coins that should have had had them. The worst the 2009 Ultra High Relief coin that the mint sent me. The polishing lines ruined the coin for me. I ultimately replaced it with a certified example.

 

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A poster on the PCGS boards asked "What Caused these spiral marks on a coin?" and showed the following photo of a 1990-D Kennedy half dollar.

 

1990d1.JPG

 

The arcs are uniform in size, occur throughout the coin including relief and tops of letters, and seem to have a common center of rotation. In these respects they resemble machining grooves made during trimming of rotating bar stock.

 

The consensus was that these are so-called "lathe lines" made when the end of die stock was machined before the design was impressed. Sounds reasonable; however....consider another idea.

 

Multiple impressions from the hub were required to create a complete working die.

As these impressions were made, all machining marks were obliterated beginning with the center and moving outward. No fine concentric lines would remain on the portrait or any other part of the finished die.

 

Notice that the photo shows concentric arcs in both the field and relief. This is not possible using pressure transfer methods. (Assuming the hub was not defective....but then we would expect to see a lot of coins with this defect.)

 

The likely cause comes from post-transfer finishing of the die.

Following its final blow from the hub, the soft steel die required cleanup. This was and remains completely normal. This was done either manually by an engraver using small tools and emery sticks, or mechanically using a rotating lap charged with abrasive. The purpose was to smooth the inevitable remaining defects. If the abrasive was too coarse or contaminated with coarse particles, they would leave concentric arcs over the entire surface. Something like this should have been caught on inspection. (At certain times, cleanup might have been done after hardening of the die – we simply do not have enough U.S. Mint practices information to make a definitive statement. Mint machinists did not routinely interact with commercial workers in the same line of business; the mints thought of themselves as holders of “secure information” of critical importance and did little writing about techniques.)

 

Most occurrences of this defect show a center point of rotation of the abrasive lap. That means the lap and die were probably in a fixed position – probably mounted in the chuck of a horizontal machining lathe. Some coins have concentric arcs with different (multiple) centers of rotation. These were likely done with a small manual lapping tool much like a tiny disk sander.

 

This phenomenon is found on circulation coins and proofs from the pre-WW-II period, and commemorative halves, among other coins.

 

I generally disagree.

 

The arcs are too perfectly concentric and too evenly spaced to have been caused by any hand finishing of the die. The assumption is incorrect that any machining marks on the blank die face will be 100% eradicated by the hubbing process. And even if the die was subjected to some post-transfer marks, those marks would affect the fields differently than the tops of the letters. That the circular marks are consistent up and over fields and devices alike is proof that they originated on the hub or die BEFORE it was hubbed.

 

Having over-struck thousands of coins, I have observed that marks on the host coins will persist to a greater degree than one would think, even after multiple strikes at very high tonnage. Even the subtle difference between a burnished blank and an un-burnished blank is evident after striking. Even a slight difference in planchet surface texture can show through after striking or hubbing.

 

Some early commemorative coins have a different type of lathe lines. Master hubs can have lathe lines if there is some "slop" in the Janvier reduction machine.

 

Here is a US Mint medal with some lathe lines that I believe are from the reduction process. This picture doesn't show them very well, but they are there (across the date area). One characteristic of lathe lines from the reduction process is that the lines tend to trail off of some of the devices (such as corners of letters, etc.). This particular 34mm medal suffered from a rather "fuzzy" reduction which may have used an original 3" medal instead of the usual larger galvano. Note the (lack of) sharpness of the date digits compared to the "D" mint mark (which would have been punched into the die after the hubbing).

image015.jpg

 

 

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I could see how the concentric lines on the fields could be caused by die clean up after the final blow from the hub, but I just can't see how the spacing on the devices would remain so concentric.

 

While I'm no expert in stamping, I just think there has to be another answer.

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The amount of abrasion necessary was very small. If the abrasive were all of the same grit size it's unlikely anything would be noticed. It's only when "something is not quite right" that we see coins with this effect. It also varies from instance to instance and the "groove" sizes differ.

Also, differences in relief are measured in thousandths of an inch; a bit of excess pressure and everything has arcs.

 

To presume the effect seen on this half or other coins is from incomplete or defective transfer from the hub, is to assume an extraordinary level of incompetence by the die sinkers. The "universe" of dies has hundreds of thousands of items. Mistakes and occasional shortcuts are inevitable, but they are not the normal product.

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Question: When did the Denver Mint start 'single squeezing' their own dies?

 

Also, check out this informative web page, pretty much covers die making processes from start to finish.

 

Denver Mint die making process

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Question: When did the Denver Mint start 'single squeezing' their own dies?

 

Also, check out this informative web page, pretty much covers die making processes from start to finish.

 

Denver Mint die making process

I need to bookmark that page! Thanks!

 

As for the lathe lines? My understanding is that these originate when the initial "cone shape" is created on the die face. These lines can be seen in a couple of the pictures from the above web page.

 

Die-Blanks-at-Denver-Mint_zpspewmuasl.jpg

 

Basket-of-Die-Blanks-at-Denver-Mint_zpshljwniad.jpg

 

The obvious goal is to eliminate the lines from the finished die but that goal was obviously not met during the production of some dies. Quality inspections or not, occasionally the obvious escapes the US Mint during the die making process. Can you say "1955 Doubled Die"?

 

Can you say "New Employee meeting deadlines"?

Edited by 19Lyds
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The amount of abrasion necessary was very small. If the abrasive were all of the same grit size it's unlikely anything would be noticed. It's only when "something is not quite right" that we see coins with this effect. It also varies from instance to instance and the "groove" sizes differ.

Also, differences in relief are measured in thousandths of an inch; a bit of excess pressure and everything has arcs.

 

"Grit" will not produce perfectly-concentric and evenly-spaced "lathe lines".

Very fine grit will polish the high points of the die face (the fields on the coin).

If a spinning disk with "grit" were applied to a die face, the effects of that would be seen mostly in the fields of the struck coin. Morgan Dollars were basined with a spinning disk of zinc oxide. And yet, not a single Morgan Dollar VAM is known to have "lathe lines".

 

Looking at that 1990-D half dollar, I estimate that the height of the arcs is less than half a thousandth of an inch (<0.0005").

 

So no, the lathe lines are not produced by any sort of post-hubbing die work.

 

To presume the effect seen on this half or other coins is from incomplete or defective transfer from the hub, is to assume an extraordinary level of incompetence by the die sinkers. The "universe" of dies has hundreds of thousands of items. Mistakes and occasional shortcuts are inevitable, but they are not the normal product.

 

Lathe lines showing through are not the result of "incomplete or defective" hubbing. They are a result of coarse machining of the die blank prior to hubbing.

 

People tend to think that metal "flows" during striking and hubbing (talk of "flow lines" and all that). But in reality, metal doesn't "flow". It bends. A relatively deep groove in a planchet or blank die face will become less deep and narrower after striking or hubbing, but it will still be visible.

 

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To repeat: The transfer process completely obliterates all traces of machining. The soft die steel does not - and physically cannot - retain machining lines while simultaneously deforming to the surface configuration of the hub. (The entire thing is similar to what happens to a planchet when it is struck by a die - only that in manufacturing a die, the metal receives multiple blows.)

 

[To help with understanding this, you must remember that when properly softened, die steel was easily sliced and cut by hand using small engraving tools. Complete dies were once made by hand cutting steel. One US Mint engraver compared it to working with frozen butter.]

 

As for the suggestion that a new or inexperienced employee just happened to find a way to selectively avoid metal deformation - nutz! The US Mint people who made dies and did other machine work were highly experienced and achieved their positions after long apprenticeship within the mint. Organizations that turn out billions of virtually identical parts every year, year-after-year, are not built on casual business processes or ignorant rubes.

 

If anyone cannot not understand this, then try a very simple (and tasty) experiment -- make a batch of mashed potatoes and plop them in a cone shape similar to the Denver Mint photos. Use a toothpick to draw 100 concentric circles with their center on the peak of the pile. When done, press a Halloween face mask into the pile. For extra realism, press and remove a couple of times. How many of your 100 circles remain? (Add good cream, butter and a bit of fresh pepper to what's left of your potato cone and enjoy.)

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To repeat: The transfer process completely obliterates all traces of machining.

 

From my experience, no it does not.

 

The soft die steel does not - and physically cannot - retain machining lines while simultaneously deforming to the surface configuration of the hub.

 

Yes, it can, and it does. I've seen it with my own eyes while working at my mint.

 

(The entire thing is similar to what happens to a planchet when it is struck by a die - only that in manufacturing a die, the metal receives multiple blows.)

 

If this were true, then why would the US Mint ever bother to burnish planchets prior to striking ? They do it because planchet texture will show through the strike (even through multiple strikes). Again, I've seen it with my own eyes. I've struck the same pair of dies on a normal planchet, a burnished planchet, and a sandblasted planchet. All three look a little different after striking.

 

"Adjustment marks" are prevalent on early US gold and silver coins. Those marks readily show through, even on the best strikes.

 

To help with understanding this, you must remember that when properly softened, die steel was easily sliced and cut by hand using small engraving tools. Complete dies were once made by hand cutting steel. One US Mint engraver compared it to working with frozen butter.

 

Frozen butter doesn't bend like metal, so I don't think that is the best analogy.

Regardless, just because one metal is soft and it is impressed by a harder metal doesn't mean the soft texture is completely obliterated. When you push down on soft metal, it is malleable and so it won't spring back. Think of the lathe lines on a soft metal surface. If you impress that with a harder object, the whole face will deform, but the soft metal won't spring back to completely fill the voids between the lathe lines.

 

If anyone cannot not understand this, then try a very simple (and tasty) experiment -- make a batch of mashed potatoes and plop them in a cone shape similar to the Denver Mint photos. Use a toothpick to draw 100 concentric circles with their center on the peak of the pile. When done, press a Halloween face mask into the pile. For extra realism, press and remove a couple of times. How many of your 100 circles remain?

 

Fun analogy, but it doesn't fit this situation. Mashed potatoes don't bend. They mush.

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I'll add another contribution to the discussion in that I think using the term "blow" is improper with regard to the hubbing process of die making as hubs are actually "pressed" into the Master Die surfaces. Often referred to as a "squeeze" instead of a "strike" (blow).

 

The correct words help folks to better visualize the die making process.

 

BTW, here's an image of a nickel I pulled off of eBay:

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-01_zpsbf5ugogd.jpg

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-02_zpsoqxewg8h.jpg

 

 

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Die polishing can really make a mess of a coin that would otherwise be quite beautiful. Here's what the mint sent me for the 2009 Ultra High Relief $20 gold. The die polishing ruined the look of the coin for me. I ultimately replaced it with an MS-70 graded piece after the prices came down a bit.

 

2009UHR20O_zpse257f1e3.jpg2009UHR20R_zps92c80af6.jpg

 

The mint really should not ship coins like this when they are charging a large premium over the melt value.

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To repeat: The transfer process completely obliterates all traces of machining.

 

From my experience, no it does not.

 

The soft die steel does not - and physically cannot - retain machining lines while simultaneously deforming to the surface configuration of the hub.

 

Yes, it can, and it does. I've seen it with my own eyes while working at my mint.

 

(The entire thing is similar to what happens to a planchet when it is struck by a die - only that in manufacturing a die, the metal receives multiple blows.)

 

If this were true, then why would the US Mint ever bother to burnish planchets prior to striking ? They do it because planchet texture will show through the strike (even through multiple strikes). Again, I've seen it with my own eyes. I've struck the same pair of dies on a normal planchet, a burnished planchet, and a sandblasted planchet. All three look a little different after striking.

 

"Adjustment marks" are prevalent on early US gold and silver coins. Those marks readily show through, even on the best strikes.

 

To help with understanding this, you must remember that when properly softened, die steel was easily sliced and cut by hand using small engraving tools. Complete dies were once made by hand cutting steel. One US Mint engraver compared it to working with frozen butter.

 

Frozen butter doesn't bend like metal, so I don't think that is the best analogy.

Regardless, just because one metal is soft and it is impressed by a harder metal doesn't mean the soft texture is completely obliterated. When you push down on soft metal, it is malleable and so it won't spring back. Think of the lathe lines on a soft metal surface. If you impress that with a harder object, the whole face will deform, but the soft metal won't spring back to completely fill the voids between the lathe lines.

 

If anyone cannot not understand this, then try a very simple (and tasty) experiment -- make a batch of mashed potatoes and plop them in a cone shape similar to the Denver Mint photos. Use a toothpick to draw 100 concentric circles with their center on the peak of the pile. When done, press a Halloween face mask into the pile. For extra realism, press and remove a couple of times. How many of your 100 circles remain?

 

Fun analogy, but it doesn't fit this situation. Mashed potatoes don't bend. They mush.

 

Do you have any pictures?

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Soft die steel "mushes" under pressure. And, yes, die transfer is better called "pressing" or "squeezing" although the machinery used was a hydraulic press, coin products of which are commonly called "strikes." For the final time: one cannot transfer hub relief into die stock while also retaining finely detailed machining grooves.

 

As for counterfeiters - they operate in their own way and in their own tiny experiences; they clearly lack the training, experience and knowledge of US Mint diesinkers.

 

I've presented accurate information based on materials and processes used at the US Mint. Those who care to believe old numismyths, illogical hearsay, and hide in their cocoons may certainly do so.

 

Those who think the concentric grooves are remainders from machining die stock should ask the Philadelphia or Denver Mint Plant Managers about the phenomenon.

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I'll add another contribution to the discussion in that I think using the term "blow" is improper with regard to the hubbing process of die making as hubs are actually "pressed" into the Master Die surfaces. Often referred to as a "squeeze" instead of a "strike" (blow).

 

The correct words help folks to better visualize the die making process.

 

BTW, here's an image of a nickel I pulled off of eBay:

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-01_zpsbf5ugogd.jpg

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-02_zpsoqxewg8h.jpg

 

 

Why do these lines remind me of 'seismic waves'? Or a stone thrown into the water where the waves radiate outward in a concentric circle?

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I'll add another contribution to the discussion in that I think using the term "blow" is improper with regard to the hubbing process of die making as hubs are actually "pressed" into the Master Die surfaces. Often referred to as a "squeeze" instead of a "strike" (blow).

 

The correct words help folks to better visualize the die making process.

 

BTW, here's an image of a nickel I pulled off of eBay:

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-01_zpsbf5ugogd.jpg

 

2008-D%20with%20Concentric%20Lathe%20Marks-Rev-02_zpsoqxewg8h.jpg

 

 

Why do these lines remind me of 'seismic waves'? Or a stone thrown into the water where the waves radiate outward in a concentric circle?

Because that's what they look like?
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Soft die steel "mushes" under pressure. And, yes, die transfer is better called "pressing" or "squeezing" although the machinery used was a hydraulic press, coin products of which are commonly called "strikes." For the final time: one cannot transfer hub relief into die stock while also retaining finely detailed machining grooves.

 

As for counterfeiters - they operate in their own way and in their own tiny experiences; they clearly lack the training, experience and knowledge of US Mint diesinkers.

 

I've presented accurate information based on materials and processes used at the US Mint. Those who care to believe old numismyths, illogical hearsay, and hide in their cocoons may certainly do so.

 

Those who think the concentric grooves are remainders from machining die stock should ask the Philadelphia or Denver Mint Plant Managers about the phenomenon.

 

Don't you mean "softened die steel" vs "soft die steel"?

 

Also, coins are struck while dies are pressed. Both use a hydraulic press of sorts but one is a quick "blow" while the other is a slow squeeze.

 

Both cannot be referred to as strikes.

 

And for the record, Daniel Carr has a lot more experience than most give him credit for and will ever understand.

 

Maybe it's time for Mike Diamond to come in and offer a physiological perspective over what does and does not occur?

 

Never mind. I see that he is a co author of the following web page:

 

Concentric Lathe Lines

 

CONECA representatives offer the page below:

 

Lathe Lines

 

So.........I guess we must all live in "cocoons".

 

(waiting for a snippy response)

Edited by 19Lyds
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Never mind. I see that he is a co author of the following web page:

 

Concentric Lathe Lines

 

CONECA representatives offer the page below:

 

Lathe Lines

 

So.........I guess we must all live in "cocoons".

 

(waiting for a snippy response)

 

Both of those links repeat the traditional numismatic belief. What Roger is trying to do is to correct these beliefs, based on the research that he has done. When new research comes out, it makes sense to study and listen to it. You can choose to accept or reject it, but the old theory (represented in those links) must be examined in the light of the new data.

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Well, here is my "two cents." I would think an abrasive that would be used to polish an item would cause less of a footprint than an object used to gouge. Difference between "cut," and "carving" versus "polish." Cut and carve would leave a noticeable footprint, polish would leave substantially less. Then, consider the amount of coins that this displays on, which appears to be very minute; I would lean towards the "cut" and "gouge" lathe created die that didn't receive the necessary polishing because mint employee was hungover or was looking at the clock! This is a new phenomenon that I was never aware of until RWB brought it to my attention!

 

Thanks RWB and dcarr for your splendid discourse.

 

 

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Never mind. I see that he is a co author of the following web page:

 

Concentric Lathe Lines

 

CONECA representatives offer the page below:

 

Lathe Lines

 

So.........I guess we must all live in "cocoons".

 

(waiting for a snippy response)

 

Both of those links repeat the traditional numismatic belief. What Roger is trying to do is to correct these beliefs, based on the research that he has done. When new research comes out, it makes sense to study and listen to it. You can choose to accept or reject it, but the old theory (represented in those links) must be examined in the light of the new data.

Sorry, but if you read the text of Jason's page, it states:

 

"Ken Potter, of CONECA, has stated that he had a conversation with a Philadelphia Mint spokesmen about the occurrence of these coins (K. Potter CONECA website),”…[the Mint Spokesman] suspected that they probably had not polished the die blanks sufficiently to remove all the lathe lines."

 

I've sent Mike Diamond a request to look at this thread and offer his opinions.

 

And its NOT that I am not open to new ideas regarding "numismyths" but some things have been said which simply are not true.

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Soft die steel "mushes" under pressure. And, yes, die transfer is better called "pressing" or "squeezing" although the machinery used was a hydraulic press, coin products of which are commonly called "strikes." For the final time: one cannot transfer hub relief into die stock while also retaining finely detailed machining grooves.

 

You seem pretty sure about that. How about a wager ? Say, $5,000. If that is too rich for you, I'd do it for as little as $1, purely for the satisfaction.

Terms:

We both send our wager to a neutral 3rd-party arbitrator.

I will invite a neutral observer over to my mint and I will demonstrate.

The demonstration will involve scratching the face of a soft A2 steel die. A previously-engraved and hardened A2 die will be pressed into the soft scratched blank die face, deep enough to get a complete transfer of the design from the hardened die. Then we will see if the scratches are still visible in the pressed design area.

 

As for counterfeiters - they operate in their own way and in their own tiny experiences; they clearly lack the training, experience and knowledge of US Mint diesinkers.

 

I've presented accurate information based on materials and processes used at the US Mint. Those who care to believe old numismyths, illogical hearsay, and hide in their cocoons may certainly do so.

 

Those who think the concentric grooves are remainders from machining die stock should ask the Philadelphia or Denver Mint Plant Managers about the phenomenon.

 

You have presented incorrect information, to the disservice of the readers of this forum. You may have interpreted what you have read from historical Mint anecdotes and formed an opinion form that. But your conclusion is wrong. Do you have any degree/training/experience in the fields of metallurgy, materials science, mechanical engineering, structural engineering, or the like ? Reading about something is not the same as actually doing something.

 

I have a degree in Mechanical Engineering and I have "been there and done that".

 

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There kinds of concentric lines have been on coins/dies for 100s of years. Whatever process made them, this should be taken into account. Here are two Conder tokens where you can see the concentric lines that were transferred onto the planchet from the dies during striking. This is well before drills were around but certainly they had lathes back then? Pretty common to see them on Conders.

 

Best, HT

 

On the reverse they are shown here in the field below 'RIDGWAY' and continue in both directions concentration around the center point.

 

DH-396BMiddlesexNGCMS64_zps310d59f2.jpg

 

You can see the concentric lines pretty well on both sides on this one:

 

DH-75MiddlesexNGCMS64RB.jpg

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[crickets ...]

 

So, my offer of a wager was communicated but not accepted or even acknowledged. Some people have no sense of sportsmanship. :eyeroll:

 

Anyway, here are the results of a test I conducted.

 

First, the implements of the test:

Back left - 39mm blank die, unhardened (soft) A2 steel;

Back right - 16mm engraved die, hardened A2 steel, to serve as a "hub";

Front - engraving bit to serve as a scratching tool (0.004" cutting tip radius).

all.jpg

A relatively small diameter hub was chosen so as to accentuate the penetration of it into the larger die face.

 

Hub face:

hub.jpg

 

Scratching tool tip:

scratch_tool.jpg

 

Prior to hubbing, I marred the soft die face by holding the tool between my fingers and dragging it across the die face multiple times in a roughly-parallel direction. I also used a "Dremel"-like tool with a small cutting disk to put two larger parallel paths of grinding marks across the middle of the die face.

 

I used my small hydraulic press to perform the hubbing. It took a few tries until I achieved the depth of penetration that I wanted. This side view of the die face shows the depth of penetration and the shearing on the side wall of the penetration (arrow). The depth of this penetration is about 0.050 inches. For comparison, the total (maximum) depth of relief for most large coins is about 0.010 to 0.015 inches. For high-relief coins, such as the Oregon Trail half dollar, this figure is closer to 0.025 inches. So the overall depth of penetration on this hubbing test is roughly twice the maximum depth of relief on an Oregon Trail half dollar.

edge.jpg

 

The scratches remain. In fact, the hubbing barely even phased them.

face_1.jpg

 

See arrow. Note how the die steel around the hub impression warped (bent). Again, metal doesn't really "flow". It "bends".

face_2.jpg

 

Close-up image confirms that the scratches barely changed, even though the steel in the hubbing area was pushed down by a distance which is orders of magnitude greater than the depth of the scratches.

face_3.jpg

 

Edited by dcarr
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Regardless of your opinions of Dan's over strikes I don't think you can really challenge the real life experience he has. I think the saying "those who can, do. Those you can't, teach" Is very applicable here. It's unfortunate RWB bowed out of this conversation but he did hold true to one end of the obvious challenge from Dan to either put up or shut up. Thanks for the demonstration Dan, it doesn't look like those marks were "obliterated" to me.

 

Nick

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Regardless of your opinions of Dan's over strikes I don't think you can really challenge the real life experience he has. I think the saying "those who can, do. Those you can't, teach" Is very applicable here. It's unfortunate RWB bowed out of this conversation but he did hold true to one end of the obvious challenge from Dan to either put up or shut up. Thanks for the demonstration Dan, it doesn't look like those marks were "obliterated" to me.

 

Nick

 

The mint uses conical dies, which deform to flat. Dan used a flat die and put deep scratches into it. I don't see the issue as settled at all - merely obfuscated.

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Regardless of your opinions of Dan's over strikes I don't think you can really challenge the real life experience he has. I think the saying "those who can, do. Those you can't, teach" Is very applicable here. It's unfortunate RWB bowed out of this conversation but he did hold true to one end of the obvious challenge from Dan to either put up or shut up. Thanks for the demonstration Dan, it doesn't look like those marks were "obliterated" to me.

 

Nick

 

The mint uses conical dies, which deform to flat. Dan used a flat die and put deep scratches into it. I don't see the issue as settled at all - merely obfuscated.

 

The average depth of the scratches is about 0.0015 inches. They are not "deep". Lathe marks on the conical die blank could easily be far deeper than that. The penetration of the "hub" in my test was about 0.050" on average (over 30 times the depth of the scratches).

 

And remember, the lathe lines seen on the struck coins in question are generally more visible towards the rim and less visible in the center. Due to the conical shape of the die blank, near the rim the depth of penetration of the hub into the die blank is not going to be much more than 0.050 inches, if that.

 

If you have some evidence to the contrary, please post it here for review.

 

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