why 120 degree for stainless not 118

Exam question

When drilling stainless steel, use a

A.drill ground to 120 °, slow cutting speedCorrect
B.drill ground to 90 °, fast cutting speed.
C.drill ground to 90 °, slow cutting speed.

Explanation

Stainless steel is drilled with a drill ground to about 120° at a slow cutting speed.

Budi S.

asked · 22 Aug 2026

Author

always use 118 degree drill for normal jobs. why stainless need 120 and slow speed, not fast like i thought for harder metal. is it because it work hardens if you go too fast? anyone know the actual reason not just the answer

Discussion1

Deepak

25 Aug 2026

i had the same question when i was doing my apprenticeship. old guy at the hangar told me stainless is a pain cos it work hardens fast. if you go too fast or the drill gets hot the metal right around the hole gets even harder and then the drill just skids and burns instead of cutting in. thats why slow speed. and the 120 point is a bit more blunt than the normal 118, gives the tip more strength so it dont chip on the harder metal. basically flatter angle plus slow speed = less heat = less work hardening. i just remember it as stainless = slow and blunt lol