NEW YORK CITY: As a way of putting yourself through school, it beats flipping burgers. Still, it couldn't go on forever, and Tuesday, three Columbia University students and one accomplice were charged with counterfeiting after they used a University color copier to churn out $80,000 in fake $20 bills over the last six months. The copies the students turned out were so successful that local bars and businesses at first accepted them without question. They were finally detected in a bar last May and traced to a copier in the printing office of Columbia's Journalism school. The scheme ultimately began to unravel when Secret Service agents caught a man spending some of the phony bills and persuaded him to cooperate. Court documents show that the four-man forgery ring was not satisfied with the small time and was about to expand its operations to Chicago and Washington. The scheme began when Columbia student Clifford Evans asked Edward Olulenu to copy a few twenty dollar bills on the Journalism school's printer. Soon, Derek Warren and non-student Keith Blackwell were recruited to sell the bills. When Blackwell was finally arrested on November 25 he was trying to sell $1060 for $300, and when Olulenu was nabbed, he had $10,000 in forged bills stashed in the trunk of his car. More arrests are expected.