Most of us have a general idea of what it takes to weld two pieces of metals together. This general idea usually incorporates an electric current or flame to heat up and melt the metal. But there is another method that is especially suited for welding round parts together, called “Inertia welding” or “Friction welding”. The basic idea is to rub the parts together so fast that friction heat it up to its melting point. In this video from Doug W a specialized machine for inertia welding is used, but any metal lathe with enough torque should do as well. Just make sure you punch the break when the melted metal is squeezed out, in order to get the strongest weld.