Fused filament fabrication (FFF) is a 3D-printing technology in which melted thermoplastic filament is extruded through a nozzle on the building bed over the previously solidified layer. This machine enables the fabrication of highly customized and lightweight objects, which are useful in the electronics, biomedical, aerospace and automotive industries. However, FFF 3D-printing is yet not widely used in industry due to the high printing times required. To reduce the printing times, different methods have been applied by researchers, such as nozzle adjustments and the introduction of parallel robots in the FFF machine. We have also developed such a high-speed FFF 3D-printer in the Laboratory of Manufacturing Technology of the School of Mechanical Engineering of the National Technical University of Athens (NTUA). This machine is based on an advanced electromechanical system that allows precise nozzle movement and filament deposition. This novel machine allows us to achieve speeds up to 350[mm/s], while minimizing losses regarding the quality and mechanical strength of the fabricated object. The construction of this high-speed FFF 3D-printer has already been optimized and now the testing phase has begun. The aim of this study is to give an in-depth analysis of the development of this machine (hardware and software) and to investigate the effect of this FFF 3D-printer on the dimensional accuracy of the 3D-printed objects. Specifically, resolution holes with diameters of 4[mm], 3[mm], 2[mm], 1[mm] and 0.5[mm] were built with different printing speeds (150, 200, 250 and 350 [mm/s]) according to the ISO ASTM 52902-2021 standard and the measurements were obtained using a microscope. The results showed that the current FFF 3D-printer achieved acceptable dimensional accuracy (errors below 10%) even for the highest printing speeds. Moreover, the slight decrease in dimensional accuracy observed as the printing speed increases is probably, due to the amplification of oscillation and elasticity phenomena (elasticity of the belt-driven system) in the 3D-printer.