what was his contribution as a chief coiner?
He put aside interesting foreign coins sent to the mint as bullion. These pieces became the Mint's Cabinet, or coin collection.
Chief coiner
Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. These pieces became the Mint's Cabinet, or coin collection. 
who was adam eckfeldt? John Adam Eckfeldt was a worker and official of the United States Mint. when did he start designing coins? 1793 which coins did he work on in the mint? 1792 half disme
Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. These pieces became the Mint's Cabinet, or coin collection. To fill gaps in this collection, he used old dies to strike postdated coins. He improved the machinery, and set aside the "master coins" and interesting foreign coins. Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion.
Adam Eckfeldt Adam Eckfeldt Adam Eckfeldt
Chief coiner Chief coiner Chief coiner
Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. These pieces became the Mint's Cabinet, or coin collection. To fill gaps in this collection, he used old dies to strike postdated coins.   he continued to improve the machinery at the Philadelphia Mint.

Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. T
wiki:5691771
Adam Eckfeldt [SEP] Chief coiner
On the death of the first chief coiner, Henry Voigt, in early 1814, Eckfeldt was appointed by President James Madison as successor. He served in that capacity for a quarter century. During his tenure, he continued to improve the machinery at the Philadelphia Mint. Eckfeldt set aside "master coins"—coins struck with extra care using new dies and polished planchets. He also put aside interesting foreign coins sent to the mint as bullion. These pieces became the Mint's Cabinet, or coin collection. To fill gaps in this collection, he used old dies to strike postdated coins. Specialists have discovered that some dies he chose for this purpose had not been used together to strike coins for commerce, thus creating unique specimens.