PART VI. Striking Errors:
Machine Doubling:
Multiple machine doubling in one direction:
Definition: Machine Doubling is the product of die instability and displaced energy from the original strike that involves either a die rebounding off of the surface of the coin; or from a shift or turn of a die after the initial strike. The resulting impact largely affects struck devices on the coin. In its rudimentary form it is very common. In the extreme it can grossly distort devices or in some cases mimic a double strike. The doubling can also become tripling or quadrupling if the energy of the original strike rebounds and returns multiple times. Also called: machine doubling damage, machine damage doubling, mechanical doubling, strike doubling, shift doubling, ejection doubling, shelf doubling, shear doubling and field doubling.
Machine doubling can in one direction rebound more than once. Below are two examples of machine tripling; the first on a Lincoln memorial cent and the second on a Jefferson nickel reverse. In the case of the Lincoln, most of the motto displays machine doubling, whereas the ES and a fragment of the T show localized machine tripling.
The image to the right shows a D mintmark on a 1936 Washington quarter. Two things that are unusual about this anomaly are, first it is isolated machine doubling. No other design element near the mintmark shows any signs of machine doubling. This isolation may be caused by the mintmark being a bit higher (sunk deeper into the die) than the surrounding design elements and more prone to being “hit” by the retreating die that causes this anomaly.
Careful examination of this machine doubling shows at least three different steps or “hits”. Two actions may have caused this phenomena; a chattering anvil die or a resonating coin.
Like any solid material, a coin will vibrate or resonate at a certain frequency when struck. In that very brief moment that the coin does come into the second contact with a die, the vibrations generated by the coin will cause the multiple steps of machine doubling to occur with just one contact of the coin to the die.
Image is courtesy of Ed Nieko
