Abstract: In a numerical control apparatus, a speed difference ?S between a program command value Sc of spindle speed and a spindle rotational speed Sov to which a spindle rotational override is applied is determined. From the speed difference ?S and a pitch command value P and a response sensitivity K of a servo system during thread cutting, a follow-up error variation ?Z of a feed axis caused by the speed difference ?S is calculated. The follow-up error variation ?Z is converted into a delay time Td of a movement start of the feed axis based on the thread pitch command value P during the thread cutting. And the movement start of the feed axis is carried out behind the converted delay time Td.

Abstract: In a numerical control apparatus, a speed difference ?S between a program command value Sc of spindle speed and a spindle rotational speed Sov to which a spindle rotational override is applied is determined. From the speed difference ?S and a pitch command value P and a response sensitivity K of a servo system during thread cutting, a follow-up error variation ?Z of a feed axis caused by the speed difference ?S is calculated. The follow-up error varitation ?Z is converted into a delay time Td of a movement start of the feed axis based on the thread pitch command value P during the thread cutting. And the movement start of the feed axis is carried out behind the converted delay time Td.