For out polycord welding we milled out a simple assembly like above.
Two 1" blocks of aluminum are attached to a rail system on a base. The tops are notched to cradle the polycord.
On one of the sliders there is a hole just large enough to put the polycord through. Each end of the cord is slid through and cut against the face of aluminum with a razor blade so that it's perfectly flat.
The hot knife is then held between the seated ends. Once hot the rail cradles are slid together and form a clean and even "weld"!
I can upload some photos upon request.
