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<p>[QUOTE=&quot;ToughCOINS, post: 7491862, member: 20480&quot;]Blanks are run through the upsetting mill primarily to reduce the diameter of the blanks enough to reliably feed into the collar.&nbsp; Pre-forming and pre-hardening the rim are beneficial by-products of this operation.</p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The whole reason a collar is employed in coining is to confine the planchet which tends to expand outward, and to impart a regular geometry at the edge of the coin, thus preventing what was known as &quot;splash striking&quot; in days long past. </p><p><br /></p><p>The confinement of the coin by the collar is what facilitates bringing up the central details.&nbsp; Since significant diametral clearance exists between the ID of the collar and the OD of the planchet, metal must flow outward to fill that void before metal begins to rise into the recesses of the dies. </p><p><br /></p><p>The amount of volume that must be filled in the annular gap between planchet and collar can be surprisingly significant.&nbsp; This is because of the perimeter of the annulus, and the thickness of the rim to be formed.&nbsp; I&#039;m at lunch at work, and don&#039;t have coin and collar specs at hand, but if the planchet is .5mm smaller than the collar, and the rim is 2mm thick on a coin 20mm in diameter, the volume to be filled is 31 cubic mm, which is a pretty meaningful number.[/QUOTE]</p><p><br /></p>

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