Stripping down a Optimus 930. The screw that secures the frame to the fount was proving difficult to loosen (a particularly abused 930) . Soaked in penetrating oil for a couple of days, still no movement. Heated it up, cooled it, then applied screw driver and attempted to undo. I managed to shear the head of the screw off. Removed frame, and attempted to remove the stub of the screw from the fount using pliers. The screw then sheared a second time leaving the stub in the top of the fount. Frustrating. First time I have seen it, a double shear on on a screw.