## 1 Introduction
Results revealed that in addition to the tool vibration frequency, the thickness and grain size, the used RUM tool had a significant effect on tool wear RUM was also applied for micro-drilling and milling of BK7 and Zerodur glasses in the research documented in [15]. Results found that, by using RUM the cutting forces, the edge chipping and the holes taper can be minimized by using RUM comparing to the results of micro grinding for the drilling operation. Recently, RUM was applied for milling microchannels and drilling microholes in Al2O3 materials. For example, [PERSON] et al. [17; 18] used RUM to fabricate microchannels on Al\({}_{2}\)O\({}_{3}\). The authors investigated the significance of RUM input parameters on the surface roughness, edge chipping, and dimensional accuracy of the fabricated microchannels. Results revealed that high dimensional accuracy (width and depth error \(\geq\) 5%) with smooth surface roughness (Ra = 0.27 \(\upmu\)m) of the machined microchannels could be obtained under optimal conditions of RUM parameters. RUM was also applied for drilling of Al\({}_{2}\)O\({}_{3}\) to investigate the effects of the parameters on cutting force, MRR and chipping size of the drilled holes [19; 20]. Tool wear and MRR were the outputs investigated while side milling of Al\({}_{2}\)O\({}_{3}\) by using RUM in the research documented in [21]. Another study was documented on studying tool wear [22] and surface roughness [23] while grinding of Al\({}_{2}\)O\({}_{3}\) by using RUM. Mathematical models were also developed for predicting cutting force [24] and tool wear [21] while processing Al\({}_{2}\)O\({}_{3}\) by using RUM. Other research studies were also investigated in applying RUM for machining other types of advanced ceramics such as zirconia [25; 26; 27] and silicon carbide [28] and silicon nitride [29]. For instance, an experimental investigation had been carried out for fabricating stepped hole on zirconia bioceramics in the study documented in [25]. Results indicated that the maximum MRR could be achieved at coarser grain sizes, higher feed rates and power ratings. [PERSON] et al. [28] studied the effects of RUM input parameters on the surface roughness, edge chipping and cutting force of the fabricated holes in silicon carbide materials. The authors found that the spindle speed and the feed rate have the most significant effect on all the outputs. It can be concluded from the above literature review that very few research studies have been conducted on the micro-milling of Al\({}_{2}\)O\({}_{3}\). According to the author's knowledge, no research has been found on milling pockets in Al\({}_{2}\)O\({}_{3}\) by using RUM. Moreover, the most of available studies have been limited to investigate the effects of RUM input parameters such as feed rate, spindle speed, depth of cut, frequency, amplitude and coolant pressure on the cutting force, edge chipping and tool wear of the fabricated holes and/or channels. Furthermore, the effect of tool overlapping and tool path strategies on the surface quality and dimensional accuracy of the machined parts have never been investigated in all studies conducted for the RUM of Al\({}_{2}\)O\({}_{3}\) ceramic. Moreover, the effect of the tool overlap and tool path were not considered in the studies documented on the fabrication of the microchannels through RUM [17; 18]. This is because, in those investigations, the selected sizes (widths) of the fabricated channels were equal to the diameter of the used RUM tools. On the contrary, the tool overlap and the tool path strategy are important parameters while machining the pocket. In contrast to the existing literature, the current study is aimed to analyze the significance of tool overlapping and tool path strategies on the surface roughness, the profiles, surface morphology and the MRR of the fabricated pockets. Scanning electron microscopy (SEM) is used to investigate the types of RUM tools wear.