Hot folding damascus is one of the quintessential parts of the process, and it’s always a bit fraught.
The object is to take a bar of steel at welding temperature, weaken/cut it on one side until it’ll fold easily and cleanly, then you fold it, tap it back into alignment with a hammer, flux it up and pop it into the forge to re-heat. After that, you weld it and draw it out into a bar, then repeat the process some number of times to give 2x, 4x, 8x, 16x, 32x, etc. layers in the composite billet. Japanese swords typically have 12 – 14 folds because more completely obliterates the grain in the metal, and less makes the grain too obvious.
Usually, the person making the blade will declare that they want to do a hot fold, and everyone gets ready. That means that there is a student or two standing by with a sledgehammer or a large forging hammer. When the smith places the billet on the anvil, they hold a cutter tool (a wedge on a long handle that resembles an axe or woodworkers’ maul) and the student takes a couple whacks until it’s cut enough that the metal can be folded down the side of the anvil. Then, everything gets lined up, fluxed, and it goes back into the heat.
Obviously, that’s not really a one person process unless the person is very stubborn and practiced. Farting around too long on the anvil can result in the metal oxidizing and then it won’t weld, and hitting the cutting tool off-center can result in a yellow hot billet of steel shooting around the room, and attendant excitement.
So, I thought I’d solve the problem for myself.
That’s a press die I made that carries a cutting blade I hand-ground (it took hours!) from a piece of 1/2″ thick S-7 shock-resistant tool steel.
You can see the area where the edge was forced into a hot billet, and there’s not much damage. A little bit, sure, but I can touch it up in a year or so if it gets decroded. Everything in a smith’s shop that repeatedly comes into contact with steel at welding temperature (including the smith!) oxidizes faster, so wear on contact points is inevitable.
Yesterday’s experiment consisted of taking a piece of 2″ wire rope, 6″ long, then heating it and consolidating it into a square-ish bar, then drawing and flattening the bar into a billet about 8″ long, 1.5″ wide, and 1/2″ thick. That was cut with the tool above, most of the way through, folded in half on the cut line and welded then re-drawn into a billet of about the same size, and the process repeated. Cable loses its texture pretty fast if you stretch it a lot so I thought 2 folds would maintain the inner structure. We shall see! The billet is in the annealing bin and today it’ll be cool enough to bandsaw in half so I can check for flaws in the consolidation.
Very clever and a great solution to the problem. I didn’t realize the process required more than one person!
“if it gets decroded” — I like that! Portmanteau of degraded and eroded? Nice!
You know, as soon as you described the problem my thought was that a press die would solve it, especially as you could set the depth to ensure you wouldn’t take it all the way through.
But I was expecting a wedge-shaped press die, rather than a cutting blade. I was thinking that the billet would be somewhat plastic and so an almost blunt, wedge-shaped, die would make a notch far enough in to bend the billet back. And that such a press die wouldn’t wear down very quickly. I would think that even a good cutting die would start notching itself fairly quickly.
So it’s interesting that you approached the solution in somewhat of a different way than I would have. My thought is that you would have a hydraulic press, maybe a small 5 or 10 ton, but maybe you are using a different type of press than I was imagining.
I’m sure there are other solutions as well. I mean you could even let the metal cool and then use a cold chisel to put the notch into the billet to allow it to bend back. That would be an easy one-man job, but I’m not certain how that would change the properties of the metal.
But I like the press idea. Simple, and very repeatable.
Hot cutting is so satisfying. I don’t do damascus, but I do it when forging things. It’s also a lot less faff than going to find the angle grinder
flex@#3:
You know, as soon as you described the problem my thought was that a press die would solve it, especially as you could set the depth to ensure you wouldn’t take it all the way through.
After a first session with a hydraulic press, you find that you can be very precise with it. I used the cutter to do a cut leaving about 1/16″ or less still connected. At that point, I felt like I could probably bend it by hand, but tapped it on the anvil instead. The challenge at that point is what will suck the most heat from the piece: the surface of the anvil, or a vise? I’m going to say it doesn’t matter much because the traditional way has the billet out of the forge for a lot longer, while you position it on the anvil and the student whacks away at it. By the way, in my opinion as a former analyst of “how things go wrong” I’m going to say that hot cutting is a fairly dangerous process due to the potential for the smith to get hit by a sledgehammer. There are no minor hits from a sledgehammer.
I mean you could even let the metal cool and then use a cold chisel to put the notch into the billet to allow it to bend back. That would be an easy one-man job, but I’m not certain how that would change the properties of the metal.
The current state of play for making tiled damascus is to bandsaw the bar apart, clean the surfaces, and weld them back together. Many pros do this using a cannister damascus technique because by the point they have a billet, it’s pretty valuable, and anything that risks the quality of the steel is anathematized. It’s also a lot more work that just popping it in the press for a second, hot cutting it, bending it and folding it, and putting it back in the forge – total time 10 seconds.
If you somehow cut it all the way through, then you’d just have to carefully stack the pieces after fluxing them, and carefully get it into the press once it was hot. Japanese knife-makers usually do it that way when forming the cutting edge – they just carefully place a piece of carbon steel where they want the edge to be and -bam- it’s welded, back to shaping the knife.
dangerousbeans@#4:
It’s also a lot less faff than going to find the angle grinder
True. I also worry about the cutter wheel not withstanding the heat well. Most angle grinders are intended for intense bursts of activity not long heat-generating cuts. I’ve had 2 of the gearboxes on angle grinders fail from overheating and seizing. One even caught fire, which was kinda neat.
Oh yeah, cutting wheels failing is fun. They just disappear and you get a nice sound of shrapnel bouncing off things. At least they fail in the plane of rotation