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<p>[QUOTE=&quot;ToughCOINS, post: 25867129, member: 20480&quot;]To add to this 3 year old discussion, I&#039;ve finally found a very clear illustration of the direction in which planchet metal first flows.</p><p><br /></p><p>The 1839-O Dime pictured below (photos courtesy of Bob Streets - very nice coin, by the way) has failed to fill in on the central obverse, despite grading full XF / AU.&nbsp; This is because the planchet volume intended for the central design was consumed by the collar cuds on the obverse rim (1:00-4:00 &amp; 4:00-6:00).</p><p><br /></p><p>After the outward flowing metal is fully constrained, the central devices next become the path of least resistance.</p><p><br /></p><p>To reiterate a point I made earlier in this thread, consider the coin to be a pie cut into slices (Yes, Virginia, it&#039;s true that the flow lines creating cartwheel luster on a coin are <i>not</i> parallel).&nbsp; The cross-sectional flow-area of each slice is twice at the rim what it is halfway to the center.&nbsp; The resistance to flow across the smaller area halfway from the center to the rim will be twice what it is at the rim.&nbsp; This is why planchet metal almost always flows first toward the rim, and then fills the central devices afterward.</p><p><br /></p><p>[ATTACH=full]1648590[/ATTACH]</p><p><br /></p><p>[ATTACH=full]1648591[/ATTACH]</p><p><br /></p><p>If the central devices are of limited surface area and of low relief, and if peripheral devices are considerable, this will exacerbate the delay in filling the central devices.</p><p><br /></p><p>Conversely, if the central devices are expansive, and of high relief, and if there are few peripheral devices, the centrals will fill much sooner, but still after the rim.</p><p><br /></p><p>Hopefully this helps folks understand, not only the predominant flow direction discussed in this thread, but also why coin designs must go through many changes to arrive at what works.[/QUOTE]</p><p><br /></p>

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