An employee was preparing an iron casting so the gating and risers could be removed using an abrasive torch. The employee used a piece of metal found on the ground to support the casting and keep it in a position where the risers could be easily accessed. The employee needed to adjust the sling location on the casting. After slacking the chain, the casting shifted, trapping the employee's left middle finger between the casting and the sling chain and resulting in partial amputation of the left middle fingertip.