Electrochemical micromachining (micro-ECM) is an innovative machining process capable of producing high aspect ratio (HAR), micro-holes, micro-slots, micro-channels, and micro-grooves in electrically conductive and difficult-to-machine materials. This study explores how variations in machining voltage, electrolyte concentration, and pulse time affect the performance of machining SS904L. The objective is to analyze how these parameters influence key response characteristics like material removal rate (MRR), overcut, and taper angle. Additionally, the study seeks to determine the optimal combination of electrode and electrolyte for machining Stainless Steel 904L by comparing two electrodes: copper and polygraphite, both using an NaCl electrolyte. To evaluate the impact of input parameters on MRR, overcut, and taper angle, Taguchi L9 orthogonal array was employed. Experimental results indicated that the polygraphite tool with NaCl exhibited the highest MRR, while the copper tool with NaCl had the lowest overcut. When comparing the polygraphite tool to the copper tool at an electrolyte concentration of 15 g/L, a voltage of 12 V, and a duty cycle of 55, an overcut of up to 6% was observed. A similar trend was observed in the taper angle, with the polygraphite tool having a taper angle of 8.5 degrees and the copper tool taking a taper angle of 9 degrees. In terms of material removal rate, polygraphite tool outperformed copper tool, achieving an MRR increase of 2.7 times. The polygraphite tool also demonstrated better micro-hole precision.