mechanical die doubling 10 cent 1997

Mechanical doubling, also called machine doubling or strike doubling, a form of doubling which appears on a coin and is easily confused with doubled die strikes. On a true doubled die coin, the doubling comes from a mistake in the process used to make the coin die itself. In mechanical, or machine doubling, the doubled image results from mechanical issues during the striking of the coin, such as the coin shifting during striking, or the die itself being jarred out of position as a result of vibration or improper coin press maintenance. Mechanical, machine, and strike doubling are all considered by purists to be forms of damage, and are therefore not collectible as an error coin.( source:  www.About.com)

There are two thought on how it happens. If the die is loose in the coinage press, some movement of the die can occur after the striking of the coin. At the instant the hammer die (obverse die) starts to move back up to the starting position, mechanical doubling occurs. At this point the pressure is being reduced on the die. Since the striking of the coin is complete, the minting process is complete. Anything that happens when the pressure on the dies is reduced is damage to the coins surface.

Adjustment screws that hold the die firmly in the coinage press can become loose. This is a mechanical problem, so it is called Mechanical Doubling Damage. 

One group feels the die bounces and creates a second image. The second group feels that the die twist and forms a second image. I personally feel the die does twist and that it does not bounce.(source/reference: Baker Numismatics)

Refer to red circles. There is no separation on '1', '0', '9', leaf and the flowers at the corners or on the serifs ("Serif" is the corners or ends of the letters or numbers on a coin.). The doubling has an angular appearance. 

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