A Lesson in Patience: Drilling a 500mm Hole at 0.01mm Feed
The job came in on a Wednesday afternoon. Aerospace customer, one of those jobs where the purchase order has more paperwork than the print does. The part was a Inconel 718 flange, about 150mm in diameter and 500mm long. It needed a 6mm through-hole drilled straight through the center. Tolerance on position was 0.1mm at depth, surface finish Ra 0.8. Standard stuff for that industry, except for the material. Inconel 718 is not forgiving. It work-hardens, it retains heat, and it eats cutting tools for breakfast. The recommended cutting speed for deep hole drilling in Inconel with carbide is around 40 meters per minute, which works out to about 2,100 RPM on a 6mm drill. The recommended feed is 0.02 mm/rev, which gives you a penetration rate of roughly 42mm per minute. At that rate, a 500mm hole should take about 12 minutes. ...