Removing rusty screws from a watch movement is a delicate procedure that requires a full set of watchmaker's tools and equipment. You will need precision tools in order to remove a watch movement, whether the spring-loaded mechanical version or an electronic movement, from the case. You can damage movement screw heads if you use the wrong screwdrivers. If you are preparing to remove rusty screws from a watch movement, consider that the rust is a symptom of more serious problems with the watch, which has been compromised by moisture.
Use a blunt blade to pop open the snap-down case back of the wrist watch or pocket watch. Place the watch face down in the palm of your hand if it's a screwdown case back. Place the palm of your hand on the case back and rotate counterclockwise until the case back is free from the case. Use a jar grip opener for stubborn screwdown case backs. Place the case in the watch case holder.
Use the jeweller's loupe to inspect the two screws securing the movement. If the screws are rusted it means the movement has been compromised by moisture and a thorough cleaning and oiling, if not replacement of parts, will be required.
Spray WD-40 on the head of a Q-tip and apply the soaked Q-tip to the heads of the screws. Ensure the WD-40 works its way under the heads of the screws. Allow the screws to soak.
Use a watchmaker's precision screwdriver by inserting it into the slot of the screw head. It's vital that the screwdriver tip fits perfectly into the head's slot. Some watchmaker's screwdrivers have soft tips and could bend when rotated or damage the slot. Use caution when applying the screwdriver to the screw head. Rotate the screw driver counterclockwise until the screw is free.
Use oil and a heated iron rod for especially stubborn rusted screws. Apply a couple of drops of oil around the screw head. Heat the precision iron rod over an open flame on the stove until it is red hot. Apply the rod to the screw head for about two minutes. Use the screwdriver to remove the screw head.
Use a jeweller's loupe to inspect the movement once it's removed from the case to determine whether other parts are rusty. Rusty screws and other parts should be replaced. Soak uncompromised parts in Naptha in a shot glass. Separate all cleaned parts in the parts tray.
Practice on a watch you are willing to destroy before tackling the real thing.
Never force a screw open.