With the rise of additive manufacturing, the demand for polymers has increased exponentially and many scholars are concerned about how 3D printing filaments should be reproduced from recycled plastic. This study aimed to develop a filament extruder machine, and investigate the potential of using recycled post-consumer high-density polyethylene (HDPE), one of the most widely used thermoplastics, for 3D printing filament material to make it more sustainable and environmentally friendly. A filament extruder machine with a polymer conveying rate of 1.53kg/hr was designed, its prototype was manufactured, and is used for the extrusion of recycled HDPE filament. A smooth and round-shape 1.77mm average diameter recycled HDPE filament was produced at an extrusion temperature of 220℃, extrusion speed of 20rpm, and a pulling speed of 5rpm with an average extrusion rate of 22cm/min. The recycled HDPE filament was characterized, and the feasibility of using it for 3D printing filament was determined by comparing its properties to those of its virgin counterpart and the most widely used polylactic acid (PLA) 3D printing filament. The ultimate tensile strength of the recycled HDPE filament was obtained 39.675MPa, which is comparable to the ultimate tensile strength of the most widely used PLA filament (40.746MPa), making it a viable 3D printing feedstock for rapid prototyping. According to thermogravimetric analysis (TGA), the recycled HDPE filament offers significant thermal stability with an onset degradation temperature of 430℃ and a full degradation temperature of 520℃. The recycled HDPE filament has also excellent water rejecting capability and its Fourier transform infrared (FTIR) spectrum shows the same functional groups as virgin HDPE polymer. In general, the study revealed a promising result for the use of recycled post-consumer HDPE plastic as more sustainable and environmentally friendly source material for 3D printing filament. The filament extruder machine is flexible and capable of extruding a variety of other recyclable thermoplastics, including polyethylene terephthalate, polypropylene, acrylonitrile butadiene styrene, polylactic acid (PLA), etc. Keywords: Filament Extruder, Recycling, FTIR, HDPE, 3D Printing, Thermal Stability