Most plastics are very free cutting, but are very tough and high speed tool steels will lose their cutting efficiency fairly quickly. It is therefore important to mantain the cutting edge in good condition. High speeds and feeds give the best results, both as to finish and to tool life. A high speed and coarse feed will throw the chips away and will prevent the rubbing action which dulls the tool. The table below give a general guide to cutting speed, feed and depth of cut for general machining of plastics: