How do I get a key to the cabinet on the guard's screen?

Hint 1 of 6:

The blacksmith told you what you needed to do at the beginning of this
scene.  In case you don't remember, you need to get an imprint of the lock
and a piece of metal to make the key.

Hint 2 of 6:

How to get the imprint is described in the section of the guard's screen.
See that if you need more help getting it.

Hint 3 of 6:

Have you ever heard the line about turning swords into plowshares?

Hint 4 of 6:

Well, in this case, it might be better to turn swords into keys.

Hint 5 of 6:

Give both the key imprint and the sword from one of the guards on the
guard's screen to the blacksmith and he'll make the key for you.  There's 
only one catch -- you need to step on the bellows to heat the metal.

Hint 6 of 6:

And to do that, you first need to get past Otto.  See the previous question
for more help.