How I Repaired A Latch Lock

We have a safety door outside two adjacent flats, our neighbor’s and ours. It has a latch lock – the sort that opens from the inside by turning a knob, and from the outside with a key. Its mechanism got disturbed and instead of locking when pushed or pulled closed, it started springing open again. So one had to really press the door firmly in order to lock it. If one just slammed it and went away, the door would remain open. Since the lock itself was working OK, we called a carpenter. He advised us to call a locksmith. We called a locksmith, who advised us to change the lock. Since the lock itself was OK in my opinion, I decided to fix it myself, if possible. I studied the lock in various positions of the door - fully open to fully closed.

This figure shows the lock with the door in closed position. The dark purple knob is twisted to unlock the lock.

This figure shows the lock when the door was open. The yellow slider is out, while it is within the grey part when the door is closed.

This figure shows the lock when the door was being closed. The yellow slider slid into the violet casing by pressure of the grey part.

This figure shows the lock when the door was closed casually. The grey part had sunk a little in the wooden frame of the door, and the edge of the yellow slider abutted against that of the grey part so that it could not slip into it. Then it slid out again by spring action and the door opened.

I removed the grey part, put a folded strip of card board as a filler behind it and fitted it back again, such that it became level with the purple part. Then the slider moved freely into the two parts and the lock started locking even when the door was closed casually.It took me a quarter as long to repair the thing as it did to create the art work for this blog.