The critical part when making a patchbox hinge, is the tube that will become the knuckles, on the lid and on the head. My dear friend Tom Curran made me a lid forming tool that is easy to deplicate, and since I received the one in the pictures below, I have made others with wider and narrower bases.
The pin which holds the lid to the head is usually 1/16". So select a piece of steel that is wide enough to form the full width of the box you are creating and thick enough that it won't bend, ie: 1/4" or thicker. Now create another piece of steel out of 1/16" sheet stock that is the full length of the width of the plate you have selected, and a little more than 1/16" wider than the plate is thick. With files, round over one edge of this little plate to simulate a hjinge pin. Clean the end of the plate well (file true) and one side of the little strip you've just made, flux and silver solder the two together so that 1/16" protrudes above the plate, as in the example in the picture below.
To make the hinge on your patchbox stock, first bend the lid metal at 90 degrees using your machinist's vise to create a sharp bend. Place the bent steel on top of the plate you've just made so that the shorter bent up part is right up against the raised 1/16" bead, clamp the two together in your vise right up against the bend, and with a block of wood and a hammer, bend the shorter section over the bead. You now have your lid with a hinge knuckle started. Remove the two from the vise, place a 1/16" music wire pin in the hinge you've started, and bend the tab down over it, finishing the hinge knuckle. It is a good idea to clean the inside face of the lid at the hinge area before you bend it, so that you have the option of silver soldering the tab down against the underside of the lid. Alternately, rivets will secure the tab. I've seen boxes that were not joined, and they always appear to be unfinished to my eye.
Now, made the head part of the hinge.
Mark out the knuckles of the head and lid, and with saws and files, remove the metal that is required. Here's an example...a steel patchbox on a Hawken rifle.