Installing tips & pins on cutter head, a piece of roll pin came off while driving pin in place & struck employee in right forearm. Cleaned & put band aid on it feeling that was all that needed. On 6/4/07 employee came in & showed supervisor a bump on his arm. We made a DR's appt for 6/7 at which time the DR told him to remain out of work until he had X-rays and the results back.