Upsetting rivets

I've been putting pegs and holes into the edges of the arms I'm working on to hold the vambrace doors closed.  It may be a dirty hack, but it works so well, and it can look elegant.  On the original pieces we don't see how many vambrace doors were held closed.  It's likely that closing with a strap and buckle, as seems to be the case in the Churburg #13 arms, was common, though it's weird that we don't generally see them on effigies.  Plus this solution solves issues with the vambrace door sliding well past closed, which is an issue when you're not wearing a decent gambeson and carrying a shield.  The two plates end up pinching you every time the weight of the shield shifts, and thanks to the wonders of spring steel, the process resets its self when there's slightly less weight on your arm so you get to take that ride many, many times during a fight.  It's like having those springy sheep shears attached to your arm and hungering for flesh.

It was a pain figuring out how to do this, and now that I have, it's simple to do, and something I don't want to forget.  Here's what works:
1. Take a stainless roofing nail. Use stainless because the tinned ones are going to spit a lung full of zinc at you.  The large flat head of the roofing nail is quite helpful.

2. Cut it to length long enough to pass through both the outer vambrace and the vambrace door with a little left over to keep the closure secure, plus a little more to account for the rivet shriking.  About three eighths of an inch should do it, depending on your steel thickness.  Annealing first (heating past the critical temp, a dull orange should do it, then cooling very slowly) helps, but you'll still probably want to use bolt cutters.  Stainless nails are a bitch to cut.
3. Place it head down on an anvil and heat it with a torch until it's orange hot.  You don't need it quite that hot to upset it, but it's small so it will cool quickly while you safely stow the torch and grab the other pieces and a hammer.
4. Pop the hot rivet/nail through the armour over it so it goes through the hole with the head of the nail on the inside of the armour and smack it 4 or 5 times with a heavy hammer to upset it.  Upsetting is a blacksmithing technique where you thicken the shank of the piece by striking the end hard.  We're looking for it to stay upright, but for the base to be thick enough that the rivet can't pass back through the hole.  This is best done with a heavy hammer and the heat helps tremendously.
5. This can then mate into a slightly larger hole in the opposite piece.  I chose to put the pegs on the smaller door plate and the holes on the outer vambrace plate.  As long as the pegs go on whichever plate goes inside the other you're OK.
6. If the hole is too small for the now upset (thickened) rivet, don't try to file the rivet down.  It's a time consuming pain and it's hard not to scratch the hell out of the plates around it.  Instead, either punch the hole it has to pop in and out of a little larger, or (and this is better because you get more control) put a tapered file into the hole and stir it around forcefully.  This wallers out the hole and thickens the edges.  Check for fit periodically, and you may have to grind the area around the hole smooth.
7. I'm working with two pegs per vambrace plate at the moment, which I think should secure the plates pretty well when they're under tension on the wearer.

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