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<p>[QUOTE=&quot;Tom Maringer, post: 171900, member: 7033&quot;]<b>Die doubling and machine doubling</b></p><p><br /></p><p>As a coiner I have made my share of doubled-images on coins. The true doubled-die is an artifact of the die-hobbing process. The master matrix (or hub) is pressed into a coned block of annealed tool steel to form the working die. If the impression is not quite deep enough the die-sinker will realign the die and hub and press again. Usually you can feel when the die and hub &quot;lock&quot; back in together... but sometimes there is a very slight shift of position, and a doubled die impression is made. They can be so subtle that they die-sinker may not even see it, and pass the die on to be heat-treated and sent to the press-room. I have inadvertantly made several such doubled-die impressions... even when I thought I was being meticulously careful to avoid them. The main solution to the problem is to refine the die-sinking technique so that a single push with the press created the impression and a second pass becomes unnecessary. </p><p><br /></p><p>Remember that it takes a lot of dies to make a government run of coins. Typical maximum die life is somewhere in the neighborhood of 50,000 strikes per set. So if a billion coins are to be made with a certain date and mintmark, then it will take as many as 20,000 sets of identical dies to produce them!! That is an astonishing number! So the die-production shop is itself like a small mint operation. In my experience, the doubled die impressions always occur early in the die production process because the particular requirements of the die being made are still being learned. After a few double-strikes are done in the process of determining the correct tonnage setting for the hobbing press, there would be no more die doubling errors. </p><p><br /></p><p>Machine doubling is something quite else... the idea there is that the die is perfect, but that the coin is struck twice with slight movement between strikes. It can only happen if the coin is struck twice, either on purpose (done to increase die-life by reducing press tonnage or for special proof strikes) or because of a problem in the feed and ejection subsystems. Once the coin is double-struck, the doubling image is because the second strike was not perfectly aligned with the first. This can occur in one of two ways. First, because the lower die in the set moves up and down in the collar it is not held firmly, wear or looseness in the alignment pin can cause a slight rotation of the die. Second, if the ways of the press are worn, the positioning of the upper die may be inconsistant. </p><p><br /></p><p>In my experience, the machine-doubled image will be a rather &quot;shadowy&quot; doubling by comparison with die-doubling, and on close examination the shadow image will be found to be completely flattened into the field. Die-doubling will show clearly under magnification that there is are two separate images with relief showing between them and with the second image clearly above the field in relief.&nbsp; So I agree with the other people who&#039;ve looked at the above photos of German and Spanish doubles that these are most certainly die-doubles and not machine-doubles, since they show clear relief.[/QUOTE]</p><p><br /></p>

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