Penetration Dynamics & Chip Load
Vorschubwerte beim Bohren (Vf & fn)
Penetration feed rate ($V_f$) dictates how quickly a drill plunges into a workpiece. Learn how to convert between rotational feed per revolution ($f_n$) and linear machine feed rate ($V_f$), optimize chip shape, and troubleshoot tool wear.
1. The Universal Feed Rate Formula
Vf = n × fn
Where Vf is linear penetration rate (mm/min or IPM), n is spindle speed (RPM), and fn is feed per revolution (mm/rev or IPR).
Unlike milling cutters where feed rate is often calculated per tooth ($f_z$), standard twist drill calculations treat the two cutting lips together in the single feed per revolution figure ($f_n$). Each individual flute takes exactly half of the feed per revolution: $f_z = f_n / 2$.
2. Recommended Feed per Rev Guidelines
| Drill Diameter Range | Steel Feed (mm/rev / IPR) | Aluminum Feed (mm/rev / IPR) | Stainless Steel (mm/rev / IPR) |
|---|---|---|---|
| 3.0 mm (1/8") | 0.05 mm (0.0020") | 0.08 mm (0.0032") | 0.04 mm (0.0016") |
| 6.0 mm (1/4") | 0.12 mm (0.0047") | 0.18 mm (0.0071") | 0.08 mm (0.0031") |
| 10.0 mm (3/8") | 0.18 mm (0.0071") | 0.25 mm (0.0098") | 0.12 mm (0.0047") |
| 12.7 mm (1/2") | 0.22 mm (0.0087") | 0.32 mm (0.0126") | 0.15 mm (0.0059") |
3. Signs Your Feed Rate is Wrong
Feed Rate Too Low (Under-feeding):
- Drill produces fine powdery dust or ribbon stringers rather than tight C-shaped chips.
- Chisel edge rubs against workpiece, generating severe heat.
- Rapid work-hardening in austenitic stainless steel (304) and titanium.
- Premature dulling of drill outer margin lands.
Feed Rate Too High (Over-feeding):
- Excessive axial thrust force stalling the spindle motor.
- Drill web fractures down the center split line.
- Blowout burrs and jagged breakout craters on through-hole exits.
- Severe hole oversize and drill wandering out of position.
Calculate Exact Feed Rates & Spindle Power
Solve bidirectional Feed/Rev ⇄ Feed Rate and check motor kW/HP limits.