You will need 4 HD utility blades as well as 4 3mm screws 8mm long (these can be machine or plastic type).

Install the blades as shown, make sure the knife edge is seated as deeply as it can be while laying the blade into its pocket.

Use the 3mm screws to secure each blade.

Weld your filament with your chosen method, make sure the filaments are perfectly aligned.   rough trim the joint with flush cutters.  Slip this trimmer over the filament, and run it back and forth over the joint while rotating the device around the filament.