It's not cutting edge technology, but it works.
Many of us who work on our own bikes end up hanging onto old parts that no longer have any use on the motorcycle. Maybe we're just waiting to take them to the recycling center. Maybe we keep them around as a backup in case the replacement part fails. Maybe we're just lazy. This video demonstrates why it might actually be a good idea to hang onto those old brake rotors. After the apocalypse, you can turn it into a sword.
The majority of the work is done with simple hand tools and a really hot fire, both of which will be readily available after the inevitable collapse of civilization as we know it. The blacksmith first heats the center of the rotor in the fire, then cuts it away from the disc itself. (Side note: It would be really cool to finish this "scrap" off as a throwing star. It certainly looks the part.) Then the disc itself is heated, cut, and straightened out into a straight, flat piece of metal. This takes numerous cycles of heating and hammering. The tip is cut to a sharp point, and it really starts to look like a sword.
At this point, the fabricator switches tools to a modern angle grinder. No doubt this saves a great deal of time when it comes to sanding and polishing the metal. After the apocalypse, you may or may not have electricity available to run your own grinder, but even if you don't, you'll have plenty of time to do the work by hand. It's not like you'll have to go to work anymore. The metal is polished to a shine and gets the sharp edges that make it a sword. It goes through a quenching cycle, where the metal goes back in the fire and gets really hot, then cools rapidly in water. This makes the metal stronger.
Finally, the fabricator drills holes at the bottom (again, something you could do by hand if necessary) and attaches a wooden handle. Everything gets polished smooth and shiny, and it's done. I particularly like how the holes through the original cross-drilled rotor remain in the final design, though predictably warped out round somewhat as the metal was straightened. It gives a nod to the sword's motorcycle origins, as well as providing a similar function of reducing its weight.
The final product isn't just decorative, either. Some demonstrations at the end of the video prove that this sword is useful for cutting and stabbing as well. Ironically, something designed to stop anything has become something that goes through anything. So the next time anyone gives you trouble for keeping your own brake rotors around, tell them that you need them to prepare for the apocalypse. I won't get into a gun control debate here, but I will just point out that you never need to reload a sword.