A method and an apparatus for controlling a numerically controlled
machine tool, wherein the
heat generation amount and the temperature of a drive unit including a
servo amplifier 15b and a feed shaft motor 3 are computed by a drive unit
heat generation amount computing unit 31 by
simulation, and from the computed
heat generation amount and the computed temperature, the total heat generation amount of the drive unit, the
cutting feed heat generation amount, the
cutting load heat generation amount, etc. are computed by a feed heat generation amount computing unit 39, so that the
cutting feed rate override value of the numerically controlled
machine tool 1 is computed by a cutting feed rate override computing unit 27 and effectuated by being output to a NC unit. Further, based on the temperature of the drive unit computed by a computing unit 31 or the temperature computed by a temperature data computing unit 47 or the temperature detected by a temperature detection sensor 49, etc., the proper values of the feed acceleration /
deceleration time constants τ<SMALLCAPS>r < / SMALLCAPS>and τ<SMALLCAPS>c < / SMALLCAPS>are computed and output as a ratio with respect to the set and stored initial values τ<SMALLCAPS>r0 < / SMALLCAPS>and τ<SMALLCAPS>C0 < / SMALLCAPS>thereby to control the NC commanded rate. The overheating of the feed axis drive unit is prevented while at the same time improving the
machining efficiency.