To be honest, I didn't find many images of cabinets with the lock exposed like this. That seems to have been more of a medieval habbit. But I was allready on the path of no return. I had to make a lock and it had to be like this, mounted from the outside. I think (hope) it will look great.
So, how do you make a lock? Another catalyst to this decision was the book Medieval and Renaissance Furniture. I have ordered a digital copy and read it front to back. It has a good description of these types of locks and it looked pretty simple to me. I must say that I have some metal working experience, which helps. I even have a Mig welder, while not excatly a medieval tool, it is very usefull nonetheless.
In reality it's all a bit more work then anticipated, but that's normal. I think the key is the most difficult part, because it is very visible, so it needs to look nice. So I started with the key. No idea how they made it back then. I took a length of 6 mm round stock and some 2 mm flat bar, cut to about 6mm width. I bend the flat bar around a round bar of appropriate diameter, driving it tight with a hammer to a ring shape and cut out a 6 mm slot for the round keyshank. Then welded them both together, making sure I had a bunch of welding material build up around the joint so I could shape it to form. The rest was filing.
Today I welded the bit to the other end of the shank. I'm not a great welder and I also managed to trip the circuit breaker a few times, so this didn't proceed as fluently as welding the bow of the key. Filing was also more difficult, because I didn't have much room to swing the files. But it ended up none too bad. Luckily this side of the key is mostly hidden from sight. Here is a picture of my first welding attempt.
After filing all the lumps and after polishing with some fine sandpaper, it all doesn't look too bad. Not perfect, but keys and locks from that time usually had a distinct "handmade" look over them anyway.
And here is another picture of a nice lock on a gothic cupboard, showing how they made them very elaborate in those earlier times. Mine will be more plain (If everything works out!). I think the extra bolt is a later addition when the key was lost.
And here is another interesting link about these kinds of locks: Lock smithing