# Estimating the Uncertainty of Measurements for Various Methods and 3D Printed Parts
## 1 Introduction  
Developing 3D printing technologies are increasingly competing with conventional manufacturing technologies. This is mainly due to the development of 3D printers, the increasing accuracy of the models produced, and the growing range of materials available. Nowadays, 3D printing is based on both plastic-based materials, metal powders, and ceramics. In the case of the 3D printing process, the dimensional and shape accuracy of the produced models depends on the technological parameters of the manufacturing process, which are variable depending on the 3D printing technology used. Studies of the dimensional and shape accuracy, and surface texture of models produced by 3D printing have been described in many scientific publications [1; 2; 3; 4; 5] and doctoral dissertations, but in many cases, the number of samples tested has been significantly limited. There are cases where studies aimed at determining the influence of technological parameters on the accuracy of 3D printing manufacturing have been carried out on only three or five manufactured samples. In such a situation, reporting the average value result alone is an incomplete representation of the actual result. Such situations may occur in the case of high production costs or a time-consuming process, but in the case of technologies such as FFF, they are unjustified. Therefore, in the present work, the study of the dimensional accuracy of models manufactured by 3D printing technology-FFF from the material based on pure PLA using three measuring tools, along with a comprehensive statistical analysis of the test results, was undertaken. This approach will make it possible to determine the influence of the measuring instrument used for testing and the number of samples evaluated on the value of the result. The results of metrological measurements of dimensional accuracy in many cases carry consequences regarding the decisions made on their basis, and therefore the information presented in thispublication can be used by both 3D printing technologists and decision-makers responsible for the manufacture of prototypes. In the case of technologists, decisions made based on the dimensional accuracy testing performed can impinge on decisions regarding 3D printer service, calibration, component replacement, or the ability to manufacture a custom order. For scientists, knowledge of measurement methods, and their advantages and disadvantages, can contribute to the development of appropriate measurement methods, strategy [6], and improvement of the measurement processes for 3D printed models [7; 8]. The rapid development of additive technologies observed in recent years requires the determination of the current dimensional and shape accuracy of the manufactured parts. Accordingly, research work is being carried out on the metrology of measurement of geometric quantities of models produced by 3D printing. Various measuring devices such as hand-held measuring instruments, coordinate measuring machines (CMM--coordinate measuring machine), 3D scanning (3 DS), computer tomography (CT) [9], etc., are used for this purpose. In addition, there are publications where the authors also conduct a comparison of the accuracy of the mentioned systems. Ref. [10] presents the results of measurements for the three systems analyzed: coordinate measuring machine (CMM), 3D scanning, and computed tomography for samples produced using 3D printing technology: fused filament fabrication (FFF) and selective laser sintering (SLS). The results of the study indicate differences in measurement results for the different measurement systems and point to, among other things, equal measurement procedures and parameters as the reason. Very often, when describing the results of the tests, the issues of the number of samples on which they were conducted are overlooked.