Empl.was using grinder to clean pin from the brakes of a quarry machine. His right index finger was pulled into the wire wheel causing an abrasion. The outer layer of skin was removed for 2/3 the dia. of the finger from the tip to primary knuckle. The abrasion was approx 2.5 in. After first aid, the empl.refused medical treatment,returned to work. No gloves or holding tool.