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 Replies: 19 / Views: 1,770 |
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Pillar of the Community
United States
1791 Posts |
At quick glance I thought maybe lathe lines but they would be symmetrical then. These are not.
Near the center when turning, the last 3/16" to the center can look very different than the rest of the face. This has to do with surface speed. The tool moves from the outer diameter toward the center at a given feed rate for a specific surface speed. The rpms of the spindle increase as this happens. At some point, the spindle reaches maximum rpm and so the surface speed decreases quite rapidly. Yet the feed rate stays for the programmed surface speed. Once the surface speed has decreased enough, a number of different things start happening such as tool deflection is no longer constant (tool bounces), metal tears rather than cuts, rubbing occurs because chips don't clear fast enough, etc. Surface speed at dead center is 0.
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Moderator
 United States
97904 Posts |
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Bedrock of the Community
United States
74905 Posts |
Cool find!  Errers and Varietys.
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Bedrock of the Community
United States
94367 Posts |
Interesting for sure. Can you sharpen that closeup?
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Bedrock of the Community
United States
10601 Posts |
Lathe lines are in the fields. Not sure what that is........  |
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Pillar of the Community
United States
3535 Posts |
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Pillar of the Community
United States
2745 Posts |
That texture around Lincoln is interesting, It would be nice to see some other photos there but I'm sure that is a tricky shot. It looks like the bottom of bay #7 is showing some partial concentric lines as well. Nice find NY.
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Pillar of the Community
United States
5787 Posts |
I like these "crop circles". Quote:
... This has to do with surface speed. The tool moves from the outer diameter toward the center at a given feed rate for a specific surface speed. The rpms of the spindle increase as this happens. At some point, the spindle reaches maximum rpm and so the surface speed decreases quite rapidly. Yet the feed rate stays for the programmed surface speed. Once the surface speed has decreased enough, a number of different things start happening such as tool deflection is no longer constant (tool bounces), metal tears rather than cuts, rubbing occurs because chips don't clear fast enough, etc... . This information is in relation to lathe lines correct, and not a die polishing tool? I wonder if these raised circular elements could be from polishing by a rotary tool going parallel to the surface of the die. Similar to the way it has been determined "Trail dies" are formed but having a circular look, instead of linear, when it occurs towards the center of the die. Words of encouragement are one of the major food groups.
We need to consume them regularly to thrive and grow.
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Moderator
United States
56855 Posts |
It would be great if we had a few mint technicians as members.They could answer a bunch of our questions. John1  |
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Pillar of the Community
United States
7516 Posts |
I agree with tanman, it make's a perfect sense.
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Pillar of the Community
 United States
982 Posts |
This is about the best image I can get with my camera. The coin is not cooperating. LOL. Thanks for all the great feedback on this one. My vote is also with Tanman. Die polishing and either some slight PMD, and or other die damage.  "We are all flawed, some MD and some PMD." NYI Edited by NY Islander
09/30/2024 3:17 pm
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Bedrock of the Community
United States
19226 Posts |
Likely the result of the application of a rotary mechanical 'device' (agree with Tanman2001). Slightly larger rings on nickels typically indicate heavy use in rotary coin 'ingestion' devices--think old-school insert-and-twist parking meters and arcade machines.
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Pillar of the Community
United States
5787 Posts |
Really nice closeup NYI. It does appear to be from an anomaly on the die. Quote:
Likely the result of the application of a rotary mechanical 'device' (agree with Tanman2001). Slightly larger rings on nickels typically indicate heavy use in rotary coin 'ingestion' devices--think old-school insert-and-twist parking meters and arcade machines. Tanman was suggesting the effects on this coin was the result of die polishing. Are you thinking this is PMD, like what might happen from those devices you mention? Words of encouragement are one of the major food groups.
We need to consume them regularly to thrive and grow.
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Pillar of the Community
United States
982 Posts |
PetesPockets -
My mention of possible post mint damage are the horizontal lines on the cheek and breast at 11 and 12 o'clock in my close up. Agree with consensus the circular ridges caused by a tool polished die.
"We are all flawed, some MD and some PMD." NYI |
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Pillar of the Community
United States
2739 Posts |
The first close-up photo of the reverse is interesting, but currently uninterpretable.
Error coin writer and researcher.
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Replies: 19 / Views: 1,770 |
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Posted 09/29/2024 12:54 pm
Uncirculated American Silver Eagles 
