Before a coin blank is considered ready for striking, it must be sent
through the upset mill, where it is converted into a planchet.
The upset mill consists of a rotating inner cylinder and a fixed
outer half ring. Each component has a stacked array of complementary
grooves that accommodates the blanks. The separation between cylinder
and drum is smaller where the planchet exits the mechanism.
As the disc of coin metal passes through the upset mill, it is
rolled and squeezed in the horizontal plane. This reduces the diameter
of the planchet and pushes up a low proto-rim around its perimeter.
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Upsetting has many benefits. The proto-rim facilitates formation of
the design rim during the strike and helps ensure that peripheral
details are as strongly defined as centrally located details. The
proto-rim allows the planchets to move more smoothly through Mint
machinery, as only a small portion of each planchet actually makes
contact with the surfaces they travel along. The proto-rim also
prevents the planchets from sticking together during their journey.
Finally, the proto-rim helps protect the interior of the planchet from damage.
The height of the proto-rim varies slightly between planchets, as
does the shape of the edge. In cross-section, the edge generally
assumes the shape of a low trapezoid (truncated triangle). Normal
variation can be attributed to inconsistent spacing between opposing
grooves in the upset mill, how the grooves are machined, and wear
within the grooves. A typical example of upset can be seen here on an
off-center Lincoln copper-plated zinc cent.
On rare occasions, a planchet will display a proto-rim and edge that
deviates markedly from the norm. The Feb. 27, 2012, column focused its
attention on several forms of abnormal upset. Error dealer Jon
Sullivan provides us with an image of an off-center cent with a
peculiar raised perimeter. The proto-rim is broad and flat on top,
while the edge is smoothly convex.
I suspect that this peculiar perimeter wasn’t produced in the upset
mill but is instead an example of circumferential pre-strike damage.
This hypothesis finds support in the banged-up interior of the planchet.
Other possible causes of peculiar upset include improperly machined
grooves, heavily worn grooves, experimental upset styles, and
planchets inadvertently sent through an upset mill set up for a
This column focuses on a particular type of abnormal upset that I
call the “long bevel.” In affected planchets, the highest point on the
proto-rim is considerably closer to the center the planchet, while the
edge is prolonged into a long bevel that is essentially triangular in
Two examples of long bevel upset are shown here. One is an undated
off-center Lincoln cent with a bust style last used in 1968. The other
is an off-center Jefferson 5-cent coin with a D Mint mark on the
reverse (minted before 1965). The cent is particularly interesting as
its edge shows a double bevel on each face, with the outer portion
more steeply angled. The Jan. 30, 2012, column features an off-center
1964-D Jefferson 5-cent coin with a less extreme case of long bevel upset.
I have not seen any long bevels on coins later than the 1960s.
It’s not clear which of the scenarios listed earlier offer the best
explanation for these long bevels. It’s certainly possible that they
reflect improperly machined grooves in the upset mill. It seems less
likely that they represent experimental upsets or an upset mill set up
for a foreign denomination. This is primarily because the long bevel
doesn’t make much functional sense. The medial location of the
proto-rim’s apex seems to undermine its role as a precursor to the
definitive design rim, which is located more laterally. It would only
make sense in the case of a foreign denomination with an unusually
wide design rim or one in which the design rim is adorned with dentils.
Circumferential pre-strike damage remains in contention as an
explanation. Both the cent and the 5-cent coin are slightly
underweight (3.04 grams and 4.82 grams, respectively). While these
weights still fall within the normal range of variation for their
respective denominations, they could also indicate that the missing
mass was lost to damage. The bevel on the 5-cent coin does show what
appear to be scouring marks in the form of fine concentric striations.