In electro discharge machining (EDM) the metal removal occurs from the erosive effects of high frequency sparks. Consequently the erosion rate depends on spark energy sparking frequency and the factors affecting them. However the experimental results are highly random and sometimes unexpected. Material erosion rate and surface roughness were analysed for the effect of important factors like pulse parameters (voltage current, ontime and offtime), polarity and work material. Taguchi method of experiment planning with orthogonal arrays was adopted to analyse the anomalies observed in the experimental results.