# Investigations on Factors Affecting 3D-Printed Holes Dimensional Accuracy and Repeatability
## 1 Introduction  
The ability to produce parts that meet the quality standards in terms of form and dimensional accuracy, stability, and repeatability is a critical aspect for any manufacturingtechnology. In this sense, additive manufacturing (AM) is not an exception considering the current trend towards using AM as a cost-effective, complementary solution to the traditional manufacturing technologies when it comes to mass customization production [1; 2]. A shorter and less complex supply chain is another advantage of the AM technology [3], the implementation of the on-demand and delocalized production strategies by means of material extrusion-based AM process (MEX) recently proving its benefits [4; 5]. However, there remain aspects related to the use of MEX for functional applications that require more investigation as the 3D prints mechanical properties, surfaces quality and accuracy strongly depend on parts design and process parameters settings [6]. Hence, researchers remain interested in analyzing by experimental and numerical methods, the influence of MEX parameters on different characteristics of prints, as well as in optimizing the manufacturing settings for different uses and work conditions [7; 8; 9]. In this regard, one of the aims of the current research is to investigate the dependency between the accuracy and repeatability of hole-type features and MEX process parameters, a topic not commonly addressed in the literature. This aspect is relevant as many 3D-printed parts include directly manufactured holes for accommodating mechanical fasteners or bushings that allow joining with other parts for producing assemblies or larger parts [10]. Moreover, the directly fabricated thru-holes are a common functional feature of the 3D-printed surgical guides [11; 12], with their dimensional accuracy and stability after medical decontamination also being important. The accuracy and repeatability of geometrical features in the AM field are assessed by benchmarking between processes [11; 13; 14], and by varying the process parameters values and evaluating their effect on the dimensional error of test parts manufactured using diverse AM processes [15; 16; 17; 18]. However, not many studies have addressed the effect of MEX parameter settings and axis orientation angles on the holes accuracy, despite these features seeing extended use across various domains. [PERSON] et al. [19] studied the extrusion and platform temperatures, layer thickness, and print speed for a polylactic acid (PLA) cylindrical test part with a hole, optimizing the manufacturing settings from the perspective of the part shrinkage. [PERSON] et al. [20] noted the difficulty of finding an optimal parameters combination that allow obtaining accurate prints (test part included both holes and rectangular features) when printing with relatively thick layers (0.3 mm). Holes with diameters of 13 and 25 mm were considered in [20], where analyzed parameters were the number of shells, infill pattern, cooling rate, extrusion temperature and printing speed. [PERSON] et al. [21] experimentally showed that the shell thickness, part size and printing speed correlates with the dimensional error, for instance, the smaller the hole' size the larger the mean dimensional deviation. [PERSON] et al. [22] noted that the holes with diameters less than 18 mm are 3D-printed undersized, and that the air gap parameter is not significantly influencing the holes dimensional error. Further analysis of the literature in the field showed limited existing knowledge on the effect of process parameters on the accuracy of directly 3D-printed holes of different diameters and axis orientations--in all the aforementioned research the holes were built with vertical axes.