This research studied the turning conditions of water pump center part made ofgrey cast iron by using carbide coated cutting tools. The objective was to presentthe results from the study of the effect of cutting speed on the life of carbidetools in fabricating water pump center part in order to find the optimal cuttingspeed based on minimum production cost and maximum production rate. Under the study, water pump center part was made of grey cast iron FC 25according to the JIS G 5501 standard. There were 5 types of carbide tools withcutting speeds of 600, 800 and 1,000 rev/min at a constant feed rate of 0.3 mm/revand a depth of cut of 2 mm. The criterion in considering the tool life was based onsurface roughness. The results showed that cutting speed and type of cutting tool affected thetool life. By comparing 5 types of carbide tools for price, tool life, minimumproduction cost and maximum production rate, carbide tool No.1, which is DNMG150408A,yielded the least production cost. The carbide tool DNMG150408A was the cheapest,though its tool life was in the second highest. Therefore, the carbide coated toolDNMG150408A was the best and should be selected for the operation.