A 1790 structure in the prison yard served as the work house, primarily for making nails. One goal in opening New-Gate Prison was to profitably employ prisoners, but experienced miners had little success teaching imprisoned men to work the copper mine, and that work was abandoned before the Revolutionary War began. In place of unprofitable copper mining, the General Assembly introduced nail making. In the early 1800s, prison Overseers gradually replaced nail production with trades such as shoe making and barrel making, also known as cooperage. Officials also instituted a man-powered treadmill for prisoners unskilled at other trades; in the four-story cell block where it was housed, approximately thirty men were required to walk on rotating steps to grind grain. At the height of the prison years, prisoners rose at 4:00 a.m. to work in the prison yard until around 4:00 p.m., then descended back into the mine to sleep. Prisoners were initially shackled while they worked, but that practice was later abandoned, as was allowing them to earn an allowance for making more items than their daily quota. In 1806, approximately thirty prisoners secretly made false keys in the workshop from the pewter in their clothing buttons and unlocked their chains, but the insurrection that followed ended quickly when one of the ringleaders was killed.