I have a lock which was screwed to the (metallic?) frame at the top of the patio door.
It was securely fixed at that time but over time it has become slightly loose.
I am unable to re-screw it and stop it from slightly moving whenever I try to lock it or unlock it.
How do I glue the lock to the (metallic) frame once and for all?
It sounds like the screw holes that this lock is screwed into have stripped so trying to tighten them wont do anything. There's a lot of torque put on these types of locks so I wouldn't recommend glue. You could try some longer screws or try moving the lock over slightly to find new metal to drill into. Alternatively you can scrap this lock entirely and replace the handle with a locking patio door handle. That would solve your problem and make your door more secure. Inexpensive locking handles will go for about 30-50 dollars and are relativity simple to install. Good luck
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