"What Caused spiral marks on a coin?" 0

[dcarr]

PS:

A poster on the other forum wrote this about my test and conclusion:

 

"Nicely done experiment you presented ATS, and in line with my own expectations....... (used to teach a strength of materials lab while finishing my engineering degree). "

 

So here is another professional in the field who is corroborating what I have presented.

 

Edited January 16, 2016 by dcarr

[nk1nk]

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.

 

Jason,

 

It may not be "settled" that's why I personally find it odd that RWB is apparently hiding in his cocoon as he would put it. It's probably not that important of an issue for the debate I suppose but I will say in my opinion Dan's test does debunk two things that RWB claims, that 1- all die surface imperfections would be obliterated during the transfer process and that 2- metal "mushes" I think both those are inaccurate, do you not agree? I personally don't think using a conical die would make that drastic of a difference. Jason you are a smart guy, do you think the tokens HT posted for example are from an abrasive polish on a mounted electric drill or from so called lathe lines? With all that's been presented which is more plausible?

 

Nick

[19Lyds]

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.

 

Well Dan, it looks like you're going to have to come up with a softened conical die face to illustrate that which you already know.

 

[WoodenJefferson]

There has to be some dynamics here that we do not fully understand or are missing vital information as to what causes this anomaly on modern coinage.

 

I can fully understand the Conder Tokens as rudimentary equipment was used to produce these tokens, but modern day techniques and state of the art equipment should render near perfect coinage...something is amiss.

[Conder101]

A problem with the idea of a circular spinning lap creating the lines while polishing the dies is that they are visible both on the field and on the devices which would have been recesses in the die. And the lines at time can be seen going right up to the junction of the field and devices ad continuin without a break. I don't see how a lap could do that.

 

Something else I noted in Carr's pictures. The face of the die blank appears ti have VERY fine lines running across it, much smaller than the scratches and they are still visible in the hubbed areas.

[dcarr]

A problem with the idea of a circular spinning lap creating the lines while polishing the dies is that they are visible both on the field and on the devices which would have been recesses in the die. And the lines at time can be seen going right up to the junction of the field and devices ad continuin without a break. I don't see how a lap could do that.

 

Yes, that is how I see it also.

 

Something else I noted in Carr's pictures. The face of the die blank appears ti have VERY fine lines running across it, much smaller than the scratches and they are still visible in the hubbed areas.

 

As part of the normal fabrication of a die blank, prior to engraving, the die face is ground flat and smooth. In the case of my example, there are fine grinding lines across the die face running from south west to north east in the close-up pictures. You are also correct that, in my test, those fine fines remained after the hubbing. If the die was to be subsequently sand-blasted or polished, those fine lines would be completely obliterated. But the other bigger scratches would still remain.

 

All of this illustrates the reason why the US Mint polishes the conical die faces prior to hubbing. If the polishing wasn't necessary, why would they still do it ?

 

[dcarr]

There has to be some dynamics here that we do not fully understand or are missing vital information as to what causes this anomaly on modern coinage.

 

I can fully understand the Conder Tokens as rudimentary equipment was used to produce these tokens, but modern day techniques and state of the art equipment should render near perfect coinage...something is amiss.

 

Conical die blanks are supposed to be ground smooth and polished prior to hubbing. But if they accidently skip that production step, then what you have is a "mint error". Even with the best equipment and modern technology, errors still happen.

 

Also consider this scenario:

 

Suppose a conical die blank had shallow lathe lines on it prior to hubbing. After hubbing, the die was inspected and deemed satisfactory because the lathe lines were barely visible. Even if invisible, the lathe lines are still there in the "memory" of the metal. In other words, the metal at the die surface is stressed differently where the lathe lines are. Subsequent heat-treating and die erosion during repeated striking could make them visible again.

 

[19Lyds]

Still waiting for some snippy comments.

[WoodenJefferson]

...the explanation is getting there, meaning I am less skeptical about how the mystery concentric lines end up on struck coins.

[83ahughes]