Hardened 4340 steel is used in the automotive industry in power transmission shafts and gears.Aircraft landing gears can also be manufactured from the same material. It can be cut at cutting speedsof up to 250 m/min using coated carbide tools [27]. A maximum cutting speed of 420 m/min [28]and 270 m/min [29] have previously been used in the machining of hardened AISI 4340 steel usingceramic tools. Thermally enhanced cutting can be used at higher speeds, but with greater costs andcomplications [30].