An employee was removing the gear box from an out-of-service weld manipulator in a storage area. The machine was secured so the employee only had to work with the weight of the chain and machine, which weighed approximately 30 pounds. He undid the master link in order to separate the chain and lost his grip on the chain with his right hand while his left hand was removing the chain from the sprocket. The tip of his left middle finger became pinched between the chain and the sprocket, resulting in a fingertip amputation at the first knuckle.