I recently removed the lock from the front of my 1973 Nishijin Model A machinge and took it to a locksmith to have a key made. He called me today and said he made the key, but it really doesn't do anything. I assumed the slide mechanism in the back wound move in and out using the key, but evidently I was incorrect. The key does turn, but no further action. So, how is the lock supposed to operate? You can pull on the tab on the back and it feels spring loaded. It moves freely. Here are som photos.