Build a real bell-striking clock for your PC and a fire extinguisher-striking clock.

Step 2 The bell's new clapper

The support for the bell is made from Meccano. The pictures should tell it all.
The bronze bell I found at a hardware store and sounds pretty nice. I unscrewed the orginal clapper and replaced with a 4mm 120mm long screw with washers and bolt.
The relay is a miniature one. I removed the copper contacts from the armature and glued a thin u-shaped steel wire. A small screw and nut complete the clapper.