Today I made the other pieces of this puzzle: the hinge parts (which are now covered in sawdust as I laid them out on the woodworking bench to take the photo
)
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The brass bits are 4 mm long and made from 4 mm brass tube with a 0.5 mm wall thickness (so 3 mm inner diameter). To make them as efficiently as possible, I used a 1 mm thick parting tool in the lathe to face the end, then part the tube off to length (running a 3 mm drill bit through after the facing cut to get rid of any interior burrs on the outer end):
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The rear end (i.e. the parted off face) narrows a bit due to the parting burr, but that's fine for the purpose (as long as I put them in the holes the right way round). The hinge pins are 7 mm long (ish) and made from 3 mm stainless steel bar, hacksawed to length and then chamfered by holding them in a cordless drill and rubbing on a file.
I've made 25 brass "hinge bodies" and 13 stainless steel "hinge pins": that's enough for six boxes with one spare of each part for when I inevitably drop one and lose it.
The brass "hinge bodies" get superglued into the box pieces and then the stainless steel hinge pins get dropped into the tube as the box is assembled. They couldn't be much simpler to make or use but they give a nice clean look to a hinged lid box:
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