## 1 Introduction  
Electrical discharge machining (EDM) is a modern processing machining method for materials that are difficult to use with conventional methods [1, 2, 3] as a result of high hardness, high wear resistance, and other special properties [3, 4, 5, 6, 7, 8, 9]. EDM is a machining process that removes some of the work material from the workpiece using the high temperature produced by spark discharges to erode the workpiece [3, 8, 10]. EDM is also known as spark machining, which involves spark eroding material from the conductive workpiece while it is submerged in a dielectric medium [11, 12, 13, 14, 15]. The principle of the EDM process is the controlled removal of material using an electrode as a cutting tool, which conducts electricity well and moves toward the workpiece by controlling the release of the electric current flowing through the sparking part under the machining gap [1, 3]. EDM is suitable for non-contact workpieces as it sparks in a cycle of time (on-time) and stopping (off-time) during this period, called the duty factor [1, 16]. EDM erodes the workpiece to produce the finished part to the desired shape and surface quality [17]. The EDM spark process is an eroding mechanism under a dielectric liquid substance that prevents short circuits in the discharge system, which prevents interruptions in the machining process. Using dielectric fluid to flush the system removes debris after discharge [18]. The spark discharge conducted in the dielectric fluid is suitable to machine most conductive materials, regardless of the hardness of the workpiece due to the non-contact of the cutting tool (electrode) and workpiece [19, 20]. Therefore, the quality of the EDM post-processing is high and EDM can be used with conductive materials [3, 20]. The obtained surface quality texture properties depend on the EDM parameters such as discharge current, discharge voltage, pulse duration, pulse interval, and flushing method [21, 22]. The problems of spark discharge after the cycle has finished and debris removal by flushing dielectric fluid through the machining gap to remove debris material to maintain consistent electrical conditions are yet to be addressed [3; 23]. The material removal rate is an important consideration; altering the machining gap can increase the material removal rate, as well as improve surface finish [24]. The EDM process has been widely used for manufacturing molds and dies, as well as in the aerospace and automotive industries [25; 26; 27; 28; 29; 30]. However, problems with deep hole machining or deep hole drilling often lead to undesirable surface quality and geometry problems. The debris removal efficiency is hampered by the difficulty in debris elimination, and the residual debris that returns to the conductor during the second spark appears to be recast onto the wall of the hole, resulting in a poor roughness appearance of the internal wall [31; 32; 33], as well as an undesirable shape of the holes that are not well-drilled. Therefore, many researchers have studied how to improve the deep hole machining process. However, poor machining performance based on the removal of debris material, surface quality, and machining accuracy usually occurs in deep hole drilling due to the difficulties in gap cleaning and debris removal from the sparking area [34; 35; 36]. This leads to low production efficiency. Deep hole machining and small-sized holes in the EDM process are important for improving the performed result process, which is why it is necessary to study various parameters [37; 38; 39]. The improvement in machining performance in several distinct areas has been thoroughly researched. [PERSON] et al. [20] researched the effects of electrode jump height and speed on the movement of debris and bubbles during electrical discharge machining. They showed that a large electrode jump height (mm) and jump speed (mm/min) can absorb cleaned oil (fresh dielectric fluid) into the bottom of the machining gap, resulting in more stable machining. [PERSON] et al.