In this study, the effects of the types of cutting insert, cutting speed, and feed rate on the machinability of hardened Caldie cold work tool steel have been examined. Workpieces were applied to heat treatment having its hardness increased to 60 HRC and then it was employed for hard turning. Experimental studies were employed by using two different types of cutting inserts (ceramic, CBN). Depth of cut was kept constant at 0.1 mm. Three levels were determined both for the cutting speeds (90, 120, 150 m/min), and for the feed rates (0.05, 0.1, 0.15 mm/rev). Having 20 cm(3) of chip volume machined from the hardened workpiece, wear at the cutting inserts were examined and average surface roughness of the workpieces were measured. Experimental design was performed by using Taguchi L-18 orthogonal arrays experiment set. Control factors for the ideal cutting conditions were determined by using of Taguchi technique. Effect of the control factors on the machining parameters was calculated using variance analysis (ANOVA). As a result of the study, feed rate was found to be the most effective machining parameter on the cutting force and on the average surface roughness. Furthermore, it was observed that wear occurred more in the cutting insert under the experimental conditions where the cutting speed and feed rate were used at high levels. Better average surface roughness and lesser tool wear were observed from the experimental studies in which CBN cutting tool was used, than from those in which ceramic cutting tool was used.