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<p>[QUOTE=&quot;10gary22, post: 1497009, member: 23626&quot;]I am sorry I didn&#039;t provide a better explanation of MD (Mechanical or Machine Doubling). A true double die is made when the die is engraved. Sometimes the pattern will shift slightly and the engraver, following the pattern will actually carve out extra grooving alongside and make the &quot;doubling&quot; effect. A RPM (re-punched mint mark) is just that. The mint marks were placed into the die with a hand held punch. If the engraver tapped the punch with his hammer twice not aligning it perfectly with the first one, it created that doubling effect on the mark. It&#039;s easier to visualize when you remember that raised places like the numbers and lettering on a coin are actually depressed on the die.</p><p><br /></p><p>Machine doubling happens when the dies shift slightly as they are compressed against the sides of the planchet. The rims are rolled onto the planchet before it goes into the press. The press stamps out the coin at a pretty high speed. So there will sometimes be slippage.</p><p><br /></p><p>Here&#039;s a look at the process</p><p><a href="http://www.usmint.gov/kids/coinnews/mintingProcess/" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.usmint.gov/kids/coinnews/mintingProcess/" rel="nofollow">http://www.usmint.gov/kids/coinnews/mintingProcess/</a></p><p><br /></p><p>Good luck with the searching !!</p><p><br /></p><p>gary:thumb:[/QUOTE]</p><p><br /></p>

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