Early CNC drilling process
1 Punch the center hole
2 Drilling
3 Chamfer
Post-processing without center drill
1 Drilling
2 Chamfer
The machining time is greatly reduced, but the center point is unstable (Appendix 1, data source: NACHI catalog), which may easily lead to unstable drill life. When the drill touches the workpiece, the tool manufacturer recommends deceleration, but the deceleration is unstable, and the drill is easy to be accelerated when accelerated. Damage (accelerating to 0.3mm/rev is not a professional suggestion). It is a dilemma for processors. Therefore, European and American processors tend to resume drilling center holes, especially tungsten steel drills with a top angle of 135-140 degrees, using 142-degree drills. When the center drill bit touches the workpiece, the center point is stable and can move forward at full speed.
Appendix 1
