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<p>[QUOTE=&quot;mikediamond, post: 624898, member: 1859&quot;]There are two types of machine doubling, &quot;push doubling&quot; and &quot;slide doubling&quot;.&nbsp; Push doubling creates shelving at the margin of the design and rounded doubling on interior portions of the design.&nbsp; It&#039;s caused by a die bouncing, shifting position slightly, and landing lightly on the newly struck design.&nbsp; Slide doubling smears the design and pushes metal up in a series of ridges.&nbsp; It&#039;s caused by a die that shifts laterally after reaching the lowest point of the downstroke.</p><p><br /></p><p>Machine doubling can be caused by die instability, press vibration, a loose cam, a coin that sticks to the anvil die, a mistimed feeder finger, a mistimed retraction phase of the hammer die, etc.&nbsp; A loose die is probably the most common cause.</p><p><br /></p><p>I consider machine doubling a mint error.&nbsp; Alan Herbert declared the minting process to be over as soon as the hammer die reaches its lowest point.&nbsp; This was an arbitrary (and I think ridiculous) cut-off.&nbsp; Any press malfunction that creates well-separated doubling shiould be considered a mint error.</p><p><br /></p><p>While minor examples of machine doubling are common and worthless, extreme examples are rare, eye-catching, and worth quite a bit.&nbsp; I&#039;ve seen strongly doubled Sac dollars (two sets of eyes, lips, noses, etc.) bring prices in excess of $80, even when they were accurately described as machine doubling.[/QUOTE]</p><p><br /></p>

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