The following is the Collector's Clearinghouse column from the July 13 issue of Coin World:
I dedicated the March 7, 2011, column to coins that were partially or completely split when they were struck through an intrusive machine part or piece of hardware.
The latest example of a coin severed in such a manner comes from error dealer Jon Sullivan. It’s the left side of a Jefferson 5-cent coin that was pinched off when an unknown item with a straight edge or a narrow cylindrical shape was forced down into the obverse face during the strike. The offending object is unlikely to have been a feeder because recent domestic examples are composed of relatively soft, brittle aluminum and are designed to break off when struck. However, in the absence of a date or any undistorted design, it’s possible that the coin dates back to when feeders were composed of more durable alloys. Still, I suspect the culprit is an unrelated element composed of a hard steel alloy.
The demi-coin weighs 1.08 grams (normal is 5 grams), indicating that 78 percent of the coin is missing.
The obverse face lacks any trace of design. The only feature is the ruler-straight impact zone, which takes the form of a narrow, smoothly concave surface that terminates in a knife-like edge.
The reverse face does preserve a few distorted design elements. In the upper left we see the stretched-out letter RIB of PLURIBUS. Below that are two converging ridges that demarcate a roughly triangular area. Their location strongly suggests that they represent the left side of Monticello (presumably the base). All of these design elements sit on a distorted, die-struck surface that is strongly convex in vertical cross section. This curved surface terminates on the right in a narrow bevel that contributes to the sharp edge.
It seems that the obverse (hammer) die never made direct contact with the left side of the planchet. Instead, the descending die drove ahead of it the foreign object that severed the coin. As this object was being driven into the planchet, it forced the reverse face against the anvil (reverse) die. As coin metal escaped from beneath the object, the left side of the planchet was simultaneously pushed laterally and tilted upward. As the extruded metal curled toward the hammer die, the reverse design and surface topography were distorted. As the downstroke of the hammer die neared completion, the left side of the coin was pinched off and propelled out of the striking chamber.
This error is quite reminiscent of an off-center 1982 Lincoln cent that was featured in the earlier-referenced column and whose obverse face is reproduced here. The left side of that cent was pinched off when a threaded bolt was struck into the obverse face.
While a beveled, knife-like edge is characteristic of coins torn apart in the course of a struck-through error, it’s important to realize that not all sharp edges can be assigned to this cause. Sharp edges can also be generated before the strike.
Previously featured in the July 22, 2013, column, this undated, Denver Mint dime displays a bifacial bevel that, for several reasons, is thought to represent pre-strike damage. First of all, the coin was struck in-collar. Any foreign object large enough to produce damage this extensive during the strike would also probably depress the collar, producing a broadstrike. Second, unconstrained planchet expansion is necessary for complete cleavage to occur. Third, facing bevels produced as a coin is torn apart by a struck-through object will be very unequal in terms of width, angulation, and cross-sectional shape. The facing bevels on this dime are identical to each other.