A pair of plastic tubes are welded together by mounting each tube in the clamp jaws of a holder. A heated wafer is movably mounted in the gap between the tubes to cause the ends of the tubes to melt. The melted ends of the opposed tubes are pressed into contact with each other to form a welded connection. Each side of the wafer has a scoop to remove excess plastic material at the ends of the tubes to control the size of the weld connection. A pair of structural cam elements is used to create a precise spacing between each set of clamp jaws for guiding the wafer to control the plastic volume of the weld. The resulting weld is independent of rheology of plastic. The same device could also be used for disconnect purposes by cutting through a single tube and forming two tube sections. Unique double jaw construction is also disclosed.