# Estimating the Uncertainty of Measurements for Various Methods and 3D Printed Parts
## 4 Discussion  
Analyzing the test results presented in Tables 3 and 4 and Figures 9-12, one can notice some characteristic trends regarding the influence of the number of samples tested on the final result. In addition, an evaluation of the three surface geometry measurement methods used allows conclusions to be drawn about the results obtained depending on the method used. Analyzing the overall test results for 30 samples measured by the three methods, it can be seen that in the case of samples where the longitudinal seam was included in the measurements, the smallest values were registered for the measurement method using a 3D scanner, where the obtained average value was 14.95 \(\pm\) 0.011 mm. In the next order, the obtained results were as follows: CMM 15.02 \(\pm\) 0.01 mm, Dial Caliper 15.08 \(\pm\) 0.008 mm. Thus, we obtain an average result differing by as much as 0.13 mm, where such a large difference is only due to the measurement method used. In the case of measurements excluding the seam, where only two methods allowed the exclusion of this area from the measurements, the results of the diameters for 30 samples look as follows: CMM 15.02 \(\pm\) 0.009 mm, Dial Caliper 15.03 \(\pm\) 0.012 mm. In the case of the measurement with the seam omitted, the difference between the largest result and the smallest is only 0.01 mm, which is 13 times smaller than above for the measurement with the seam (CMM 15.02 \(\pm\) 0.01 mm, Dial Caliper 15.08 \(\pm\) 0.008 mm, 3D Scanner 4.95 \(\pm\) 0.011). The measurement using CMM and skipping the seam, despite taking the same average value of the diameters, has a smaller error in the form of expanded uncertainty, which is due to the fact that CMM included over 370 measurement points in the measurement strategy averaging the final result. In the case of the Dial Caliper, the difference in the average measurement value is as much as 0.05 mm, which is due to the fact that the seam/defect site was omitted from the measurements. It seems that randomly selecting a spot without analyzing the occurrence of a seam can result in an additional error of at least 0.05 mm and a larger diluted uncertainty in the measurement, which is all the easier because there are cases where the model is made with a so-called randomly scattered seam. Both cases have shown, in a great quantity of the test specimens without a seam, the difference between the measured values for the two methods blurs, as shown in Figure 10.  
Analyzing the values of the diameters, it can be clearly seen that the measurements with the exclusion of the seam are characterized by smaller average values of the obtained results, which is a natural phenomenon. It can also be seen that the values of the expanded uncertainty for Dial Caliper are significantly smaller when the seam location is omitted. Such a relationship is important from the point of view of analyzing the test results, as it can be seen that skipping the seam area more accurately depicts the actually reconstructed cylindrical surface, and the seam location slightly distorts both the result of the average diameter and the expanded uncertainty of the measurement. Dial Caliper measurement performed without knowledge of the described relationship regarding the occurrence of the seam is currently considered unreliable, since the seam is a fixed element regarding FDM/FFF technology. The research presented on this object is relevant insofar as the development of 3D printing technology in terms of the software of printers now offers the possibility to choose how to arrange the seam, for example, in a single line as was the case in the presented research, or as a scattered seam in different places of the printed object. Regardless of the chosen option, the seam as a fixed defect always occurs in FDM/FFF technology.