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 Replies: 13 / Views: 1,941 |
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Bedrock of the Community
Australia
21786 Posts |
I was examining a nice MS 1964 Kennedy. (90% silver) Very obviously, the rims are much thicker than the body of the coin. Which got me around to thinking: What, at it's very thinnest point, between the obverse and reverse fields, is the very minimum thickness of 90% half dollars? Does the U.S. Mint have any specification in this regard? If there isn't any, would it be possible for any of the 'Body of Expert CCF Members', to accurately measure the absolute minimum thickness with a micrometer screw gauge? Just curious  Thanks in advance! |
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Pillar of the Community
Australia
7096 Posts |
Quote:
I was examining a nice MS 1964 Kennedy. (90% silver)
Very obviously, the rims are much thicker than the body of the coin.
Which got me around to thinking:
What, at it's very thinnest point, between the obverse and reverse fields, is the very minimum thickness of 90% half dollars?
Does the U.S. Mint have any specification in this regard?
If there isn't any, would it be possible for any of the 'Body of Expert CCF Members',
to accurately measure the absolute minimum thickness with a micrometer screw gauge?
Just curious
Thanks in advance!
Crikey Sel you must be getting boored senseless  I have completed a full set of these coins and have many extras. Amongst these are several 1964 Kennedy halves , They all look,feel and weigh the same. Why the question? do you have a dodgy one  |
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Bedrock of the Community
 Australia
21786 Posts |
Not really. I always knew that a coin has a specified thickness, but I did not know exactly how this was actually measured:
average thickness, or
rim thickness (for stacking),
but like most coins that have a rim to help protect it during circulation,
must also have an absolute minumum thickness.
With the 90% silver halves being more dense than 40% or clad Halves, the 90% coins must have an even less absolute minimum thickness, at some point in the fields opposite each other, on the obverse and reverse.
It is just that I do not have a micrometer screw gauge, and so I can't answer that question for myself.
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Pillar of the Community
United States
950 Posts |
I think this is an interesting question.
Do you mean what is the thinnest point of the coin or what is the minnimum thickness allowed by the mint's QC standards?
The first would vary if the dies are rotated.
Edited by baysinger626
08/30/2012 12:23 pm
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Bedrock of the Community
United States
17884 Posts |
Quote:
Does the U.S. Mint have any specification in this regard? For the finished coin no. For the coinage strip the blanks are punched from yes. Quote:
If there isn't any, would it be possible for any of the 'Body of Expert CCF Members',
to accurately measure the absolute minimum thickness with a micrometer screw gauge? Since the thickness would be a function of the pressure of the strike on the individual coin combined with how well the planchet was annealed, how many thousands of coins do you think should be measured before we can fairly conclusively say what the minimum is? Edited by Conder101
08/30/2012 1:19 pm
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Bedrock of the Community
Australia
21786 Posts |
The Unc. 1964 Kennedy has rims, which need to be above the fields on both sides, so that the coins can be stacked. (same applies to almost all coins)
In order for the relief to be shown, the fields have to be below the relief detail. A lot of coin designs have slightly dished fields to accommodate the relief below rim height. The '64 Kennedy design certain does.
The absolute thinnest point on the coin would be between two opposite points in the fields, opposed to each other.
It would be at this point that the absolute minimum thickness of the coin would be measured.
Easier to measure rim thickness with a micrometer screw gage, but the diameter of the flats in the screw gauge could present some problem in the measurement.
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Pillar of the Community
United States
5606 Posts |
I believe this is a question worthy of more than words,You need a number, I will check the coin's minimum thickness with my micrometer once I can Have both in hand....... Mike.
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Bedrock of the Community
Australia
21786 Posts |
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Bedrock of the Community
United States
17884 Posts |
Quote:
The absolute thinnest point on the coin would be between two opposite points in the fields, opposed to each other. But are any two opposite field field points at the same thickness as any two others? In other words are the two fields flat and parallel to each other at all points? Then due to striking pressure and planchet annealing variance how much can this distance vary? |
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Pillar of the Community
United States
5606 Posts |
As much as ANY other coin struck, would that be safe to say!! All coins struck would vary, for the same reasons, IMO...... I will check that rough demension now....
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Pillar of the Community
United States
5606 Posts |
MY Micrometer has a "wide" indicator tip, I or anyone else will need the "Needlenose" type tip for the proper reading, which I am sure, like any other struck coin will vary, to a "unknown degree"!!!Rims vary from 0.0078-0.087 of an inch, taken from 5 different coins, thats a given......
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Bedrock of the Community
Australia
21786 Posts |
Yeah, I would figure that a needle nosed tip micrometer screw gauge would be needed, and that several readings at several opposing points would need to be taken. Hopefully, they would be field points opposed to each other.
The least of these readings would represent the absoulte minimum thickness for the coin.
I would expect that the absolute minimum thickness for a 90% half dollar would vary slightly from design to design. e.g., Walker vs. Franklin vs. Kennedy.
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Bedrock of the Community
Australia
21786 Posts |
THE ANSWER!
I have been able to obtain a borrow of a micrometer screw gauge, with domed contact points, not circular flats.
This means that opposite points in the fields at the absolute minimum thickness, can be measured.
The results:
Rim thickness:2.15mm.
Absolute minimum thickness at opposite points in the fields
1.39mm.
The absolute minimum thickness is about 65% of the rim thickness.
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Bedrock of the Community
Australia
21786 Posts |
The average thickness of a .900 fine half dollar would have to be determined by entirely different means:
S.G. Cu: 8.93 (10% by weight)
S.G. Ag: 10.5 (90% by weight)
S.G. of .900 fine half dollar: 10.343.
Mass of 90% half dollar 12.5 gm.
Volume calculates at 1.2085 cc's.
Diameter (given): 3.06 cm.
Average thickness calculates at 1.643mm.
My mental calisthenics completed for today!
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Replies: 13 / Views: 1,941 |
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Posted 08/29/2012 07:47 am
