PET Filament Joining Pliers

High-temp Filament Joiner for PET
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updated January 28, 2025

Description

PDF

Upcycled PET is more challenging to join than most filaments since it requires higher heat (250C+) and needs to be cooled rapidly to avoid crystallizing. The SunLu FC01 filament connector and various other joiners use a PTFE sleeve or material that can't survive the elevated temps required by PET.

I designed a joiner using a metal split tube to handle the higher temps. I used printed PCCF as a heat break to attach the metal split tubes using high-temp epoxy. The PCCF is fastened to PET (or PETG/PLA) jaws for some flexibility. A sheet metal seaming plier is used, and jaws are replaced with the one I designed.

Fasteners are used in most places to allow for a few degrees of alignment.

PARTS/MATERIALS LIST: 

Harbor Freight Seaming Pliers

(2) PET (or other filament) Jaws

(4) PCCF (or other high temp filament) Heatbreak parts

(4) 10-24 button head screws (replace the counter sunk pliers screws for adjustability)

(8) M3x16 button head screws (PCCF heartbreak to jaws)

High-Temp epoxy

(1) Stainless Steel 3.5mm x 1.9mm x 200mm tube (ground lengthwise to form half of a tube); which is then cut to the length of the jaws (about 2.5")

TUBE GRINDING:

I made a jig that would cradle the steel tube. A piece of wood with a groove or aluminum extrusions would work. Firmly clamp the steel tube so it can't rotate within the groove. I devised a bearing guide setup for my Dremel with a 3/4" x 3/8" diamond wheel to create the proper offset so that I could only grind so far and still leave 1.75mm remaining of the 3.5mm tube. Pro tip: insert a 14 gauge copper wire in the tube to help with heat dissipation and support the steel walls from warping. When complete, the copper wire can be easily pulled out. See attached PDF.

ALIGNMENT:

Loose fit the jaws to the pliers and then close the jaws with a piece of solid filament to align the split tubes. When the jaws are aligned and the pliers fully compressed, tighten the jaw screws in an alternating pattern to hold this alignment.

JOINING PROCESS: clamp jaws and lock pliers shut. Push equal amounts of filament into the split tube so the joint is in the middle. Heat the tube with a butane torch for about 5 seconds. Push the filaments towards each other...they should move only slightly. Then, rapidly cool the tube with compressed air or a fan to avoid the PET crystallizing. Release pliers, and the cooled filament should shrink away from the metal tube. RESET and REPEAT.

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