Stainless drilling fails more often than any other operation. Work-hardening, low thermal conductivity, and gummy chips destroy drills. Here is what works.
Stainless Steel Categories
- Austenitic (304, 316) — Most common, easiest stainless to drill (still tough)
- Ferritic (430) — Easier than austenitic
- Martensitic (410, 420) — Hardenable, hardest to drill when treated
- Precipitation hardening (17-4 PH) — Aerospace standard, tough
- Duplex (2205) — Most challenging, work-hardens dramatically
Drill Selection
| Stainless Type | Drill Type |
|---|---|
| 304/316 (light duty) | HSS-Co spiral-flute |
| 304/316 (production) | Solid carbide AlTiN through-coolant |
| 17-4 PH | Solid carbide submicron + AlTiN |
| 410/420 (treated) | Solid carbide nano-coated |
| Duplex 2205 | Solid carbide submicron + HP coolant |
Cutting Parameters
For 12mm carbide through-coolant drill in 304 stainless:
- Vc: 50-70 m/min (1,300-1,860 RPM)
- Feed: 0.15-0.20 mm/rev
- Coolant: through-tool at 70+ bar
- Peck cycle: not needed if internal coolant working
Common Mistakes
1. Speed Too High
Stainless work-hardens at high temperature. Reducing speed often INCREASES tool life.
2. Insufficient Feed
Below 0.10 mm/rev, drill rubs and work-hardens stainless. Damages drill within seconds.
3. No Through-Coolant
External coolant cannot reach cutting edge in stainless. Heat builds rapidly.
4. Wrong Coating
TiN coating welds with stainless. AlTiN or AlCrN required.
5. Letting Drill Wear Past 60% Life
A worn drill in stainless work-hardens the hole, then breaks. Index frequently.
Best Practices
- Drill straight through if possible (no peck cycles in stainless)
- Maintain coolant flow throughout cycle
- Inspect drill every 50-100 holes
- Replace at 80% expected life, not at failure
- For deep holes, use double-margin or carbide-tipped specialized drills
Tool Recommendations
- Sandvik CoroDrill 460-MM grade
- Walter A3782 with through-coolant
- OSG ADO-SUS specifically for stainless
- Mitsubishi MWS-SUS
See our HP coolant guide (similar principles for stainless).
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