▁very ▁hot ▁sw arf . ▁ ▁For ▁heavy ▁fe eds ▁and ▁compar atively ▁deep ▁holes ▁oil - hole ▁dr ills ▁are ▁used ▁in ▁the ▁dr ill ▁bit , ▁with ▁a ▁lub ric ant ▁p ump ed ▁to ▁the ▁dr ill ▁head ▁through ▁a ▁small ▁hole ▁in ▁the ▁bit ▁and ▁flow ing ▁out ▁along ▁the ▁fl uting . ▁A ▁conventional ▁dr ill ▁press ▁arrangement ▁can ▁be ▁used ▁in ▁oil - hole ▁dr illing , ▁but ▁it ▁is ▁more ▁commonly ▁seen ▁in ▁automatic ▁dr illing ▁mach in ery ▁in ▁which ▁it ▁is ▁the ▁work pie ce ▁that ▁rot ates ▁rather ▁than ▁the ▁dr ill ▁bit . ▁ ▁In ▁computer ▁numerical ▁control ▁( CN C ) ▁machine ▁tools ▁a ▁process ▁called ▁, ▁or ▁interrupted ▁cut ▁dr illing , ▁is ▁used ▁to ▁keep ▁sw arf ▁from ▁det r iment ally ▁building ▁up ▁when ▁dr illing ▁deep ▁holes ▁( appro xim ately ▁when ▁the ▁depth ▁of ▁the ▁hole ▁is ▁three ▁times ▁greater ▁than ▁the ▁dr ill ▁diameter ). ▁Pe ck ▁dr illing ▁involves ▁pl ung ing ▁the ▁dr ill ▁part ▁way ▁through ▁the ▁work pie ce , ▁no ▁more ▁than ▁five ▁times ▁the ▁diameter ▁of ▁the ▁dr ill , ▁and ▁then ▁ret ract ing ▁it ▁to ▁the ▁surface . ▁This ▁is ▁repeated ▁until ▁the ▁hole ▁is ▁finished . ▁A ▁modified ▁form ▁of ▁this ▁process , ▁called ▁high ▁speed ▁pe ck ▁dr illing ▁or ▁chip ▁breaking , ▁only ▁ret ract s ▁the ▁dr ill ▁slightly . ▁This ▁process ▁is ▁faster , ▁but ▁is ▁only ▁used ▁in ▁moder ately ▁long