Before a blank can be considered ready for coining, it must pass
through an upset mill. Here the blank is squeezed to a smaller
diameter and is simultaneously provided with a low proto-rim at the
outer margin of each face. In this way a blank becomes a planchet.
Upsetting or “rimming” provides many benefits, as listed here and
with credit to Ken Potter and Sean Moffatt.
1. The reduced diameter allows the planchet to fit easily into the collar.
2. Upsetting smooths out the rough edge left by blanking.
3. The proto-rim makes it easier for the design rim to strike up.
4. Planchets pass through machinery faster and more smoothly than
blanks, since only a narrow ring is in contact with any flat surface.
5. Planchets don’t have the same tendency to stick together that
6. The proto-rim protects the interior of the planchet from abrasion.
The upset mill consists of a rotating drum and a fixed half-ring.
Each element has a series of V-shaped grooves cut into it. The blank
is fed into a facing pair of grooves and is propelled (rolled along)
by the rotation of the drum. The distance between the deepest parts of
the facing grooves shrinks as the blank moves along the half-ring.
This gradually squeezes the blank to the diameter of a planchet.
The height of the proto-rim and the shape of the planchet’s edge
will vary within and between denominations. In cents, dimes and higher
denominations, the junction between the apex of the proto-rim and the
most lateral point on the edge is beveled. The strip in the center of
the edge is flat, however. In vertical cross-section the edge has the
shape of a truncated triangle, or trapezoid. The shape of the
trapezoid is determined by the shape of the grooves. Minor variation
in the distance between the two grooves creates variation in the
height of the proto-rim.
Planchets for 5-cent coins generally show a flatter edge and a
lower proto-rim, with a very narrow bevel at best.
Some planchets show a pattern of upset that falls well beyond the
normal range of variation. Our first example is an off-center 5-cent
coin with a pronounced proto-rim, wide bevel and narrow, flattened
Far stranger is a 5-cent coin that previously appeared in the Jan.
23 “Collectors’ Clearinghouse” column. As shown in the close-up photo,
the proto-rim is tall and wide with a sharp internal margin. A thin
pleated apron extends in from the proto-rim. The gently sloping outer
surface of the proto-rim almost looks machined. The edge of the
planchet is strongly convex in cross-section.
Neither example bears any resemblance to a typical pattern of
upset, illustrated here by a double-struck 5-cent coin. Here the edge
is wide and flat, the beveled zone is very narrow, and the proto-rim
is very low.
Atypical patterns of upset may reflect any of the following circumstances:
1. Improper machining of grooves.
2. Grooves with wear or damage.
3. Grooves with an experimental cross-sectional contour.
4. Use of an upset mill intended for another denomination,
domestic or foreign.
5. Circumferential pre-strike damage that happens to resemble the
effects of upsetting.
I suspect the 5-cent coin with the pleated apron falls into the
The next coin up for consideration is an off-center zinc cent with
just a dusting of copper plating distributed in a bulls-eye pattern.
The edge is completely flat and vertical, and the proto-rim is tall,
thin and sharp. It’s quite different from a second off-center cent
which shows a typical pattern of upset.
The minimally plated zinc cent is rather similar to our last
example, a presumed 5-cent planchet struck way off-center. The edge is
flat and the proto-rim is thin and sharp. The surface of the planchet
has an unusual bright gleam.
Other photos of oddly upset planchets can be found in the
September/October 2005 Errorscope.
Editor's note: Several images and captions were mismatched in
the Collectors' Clearinghouse column in the print and digital
editions of the Feb. 27 issue of Coin World. The images and
captions are properly matched here.
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