Introduction
Indexable insert drills — also known as crown drills or U-drills — are among the most productive tools in modern CNC machining. Unlike solid carbide drills, indexable drills allow users to replace worn cutting edges simply by rotating or changing inserts, dramatically reducing tooling cost per hole while maintaining high metal removal rates. However, achieving consistent hole quality, long tool life, and maximum productivity requires correct cutting parameter selection based on workpiece material, drill geometry, and machine capability.
This reference guide provides comprehensive cutting parameter recommendations for indexable insert drills across all six ISO material groups — P (steel), M (stainless steel), K (cast iron), N (non-ferrous), S (superalloys and titanium), and H (hardened steel). Each table includes recommended cutting speed (Vc), feed per revolution (fn), and suggested carbide grades with coatings. All values are based on general-purpose indexable drills with 2–3×D depth capability and through-tool coolant.
Indexable Drill Basics
Drill Types and Geometry
Indexable drills are classified by their depth-to-diameter ratio (L/D):
- 2×D drills — Short, rigid design for shallow holes and high feed rates. Best for mass production of simple holes.
- 3×D drills — Most common general-purpose length. Suitable for the majority of drilling applications.
- 4×D to 5×D drills — Longer reach with internal coolant supply. Requires reduced feed rates and careful alignment.
- 8×D+ deep hole drills — Specialized designs with guide pads and enhanced chip evacuation. Typically require pecking cycles.
The cutting edge of an indexable drill consists of two inserts: a central insert (near the drill center, working at low cutting speeds) and an outer insert (at the drill periphery, working at maximum cutting speed). In many designs, the central and outer inserts have different geometries and sometimes different grades to accommodate the varying cutting conditions across the drill diameter.
Key Parameter Definitions
| Parameter | Symbol | Unit | Description |
|---|---|---|---|
| Cutting Speed | Vc | m/min | Surface speed at the outer cutting edge (maximum diameter) |
| Spindle Speed | n | rpm | Rotational speed, calculated as n = 1000 × Vc / (π × D) |
| Feed per Revolution | fn | mm/rev | Axial advance per full spindle revolution |
| Feed Rate | vf | mm/min | Axial feed rate, calculated as vf = fn × n |
| Drill Diameter | D | mm | Nominal drill diameter (outer cutting edge) |
| Depth of Hole | L | mm | Total hole depth from entry surface |
General Guidelines Before You Start
- Always use through-tool coolant at minimum 10–15 bar pressure for indexable drills; 30+ bar is preferred for deep holes.
- Ensure rigid setup: short tool overhang, stable workpiece fixturing, and minimal spindle runout (≤ 0.01 mm TIR).
- For cross-holes or inclined entry surfaces, reduce feed rate by 30–50% at the break-through point.
- Start with conservative parameters and increase gradually while monitoring tool wear and chip formation.
- All values below assume emulsion coolant (5–10%) unless otherwise noted. For dry machining, reduce Vc by 30–40%.
Cutting Parameters by ISO Material Group
ISO P — Steel (Unalloyed, Low-Alloy, High-Alloy)
Steel is the most commonly drilled material in general engineering. Indexable drills with PVD-coated carbide grades deliver excellent productivity across the full hardness range from soft steel up to approximately 35 HRC. For higher hardness steel, see ISO H section.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Low-carbon steel (C10–C25) | 100–180 HB | 120–180 | 0.15–0.25 | 0.20–0.35 | 0.25–0.45 | TiAlN PVD + TiCN CVD |
| Medium-carbon steel (C30–C45) | 150–220 HB | 100–150 | 0.12–0.22 | 0.18–0.30 | 0.22–0.40 | TiAlN PVD grade |
| Alloy steel (42CrMo, 4140) | 180–280 HB | 80–130 | 0.10–0.20 | 0.15–0.28 | 0.20–0.35 | TiAlN + TiCN multi-layer |
| High-alloy steel (4340, 8620) | 200–300 HB | 70–110 | 0.08–0.18 | 0.12–0.25 | 0.18–0.32 | AlTiN PVD fine-grain |
| Tool steel (H13, D2 annealed) | 200–250 HB | 60–100 | 0.08–0.15 | 0.10–0.22 | 0.15–0.30 | TiAlN PVD wear-resistant |
Note: For steel with scale or forged surfaces, reduce Vc by 15–25% and use a more wear-resistant grade to combat abrasion from the oxide layer.
ISO M — Stainless Steel (Austenitic, Ferritic, Martensitic, Duplex)
Stainless steels present unique drilling challenges due to their high ductility, work-hardening tendency, and poor thermal conductivity. Built-up edge (BUE) is a common failure mode. Positive rake geometries and smooth AlTiN or TiAlN+TiN coatings are essential.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Austenitic (304, 316L) | 150–200 HB | 60–100 | 0.10–0.18 | 0.15–0.25 | 0.20–0.32 | AlTiN PVD + polished rake |
| Ferritic (430, 409) | 130–180 HB | 70–110 | 0.12–0.20 | 0.18–0.28 | 0.22–0.35 | TiAlN PVD grade |
| Martensitic (410, 420) | 180–240 HB | 50–85 | 0.08–0.15 | 0.12–0.22 | 0.18–0.30 | AlTiN PVD tough substrate |
| Duplex (2205, 2507) | 200–280 HB | 45–75 | 0.08–0.14 | 0.10–0.20 | 0.15–0.28 | TiAlN+TiN multi-layer PVD |
| Precipitation hardening (17-4PH) | 250–350 HB | 40–65 | 0.06–0.12 | 0.08–0.18 | 0.12–0.25 | AlTiN PVD ultra-fine grain |
Pro tip: When drilling austenitic and duplex stainless steels, avoid dwelling or pausing at the bottom of the hole, as this promotes work hardening and accelerates flank wear.
ISO K — Cast Iron (Gray, Ductile, Compacted Graphite)
Cast iron is generally considered an easy-to-drill material due to its good chip-breaking properties and lower cutting forces compared to steel. However, the abrasive nature of graphite flakes and varying microstructure (especially in CGI) requires wear-resistant carbide grades.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Gray cast iron (GG25, GJL-250) | 180–240 HB | 100–160 | 0.15–0.28 | 0.20–0.38 | 0.25–0.48 | TiN/TiCN/TiN CVD coating |
| Ductile iron (GGG40, GJS-400) | 150–220 HB | 90–140 | 0.12–0.25 | 0.18–0.35 | 0.22–0.42 | TiCN + Al2O3 CVD |
| Compacted graphite iron (CGI) | 180–260 HB | 60–100 | 0.10–0.20 | 0.15–0.28 | 0.18–0.35 | Si3N4 ceramic or AlTiN PVD |
| Malleable cast iron | 150–200 HB | 80–120 | 0.12–0.22 | 0.18–0.32 | 0.22–0.40 | TiAlN PVD general-purpose |
| High-silicon cast iron | 200–280 HB | 50–80 | 0.08–0.15 | 0.12–0.22 | 0.15–0.30 | CBN-tipped (high abrasive) |
Note: For high-volume cast iron drilling, diamond-coated (DLC or CVD diamond) carbide inserts can increase tool life by 2–5× compared to standard coated grades, especially in abrasive CGI and high-silicon grades.
ISO N — Non-Ferrous Metals (Aluminum, Copper, Brass, Magnesium)
Non-ferrous materials allow the highest cutting speeds in drilling operations. Aluminum alloys can be drilled at speeds exceeding 1000 m/min with proper tooling. The primary challenges are built-up edge (BUE) in softer alloys and chip evacuation in deep holes.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Aluminum wrought (6061, 7075) | 60–150 HB | 300–600 | 0.20–0.35 | 0.25–0.45 | 0.30–0.55 | Uncoated WC + polished, or DLC |
| Aluminum cast (A356, AlSi9Cu3) | 70–120 HB | 200–400 | 0.18–0.32 | 0.22–0.42 | 0.28–0.50 | DLC or PCD-tipped |
| Aluminum high-silicon (>12% Si) | 80–140 HB | 150–300 | 0.15–0.28 | 0.20–0.38 | 0.25–0.45 | PCD-tipped (best wear resistance) |
| Copper / Brass (CuZn38) | 60–120 HB | 200–350 | 0.15–0.28 | 0.20–0.38 | 0.25–0.45 | Uncoated polished carbide |
| Magnesium (AZ31, AZ91D) | 50–80 HB | 400–800 | 0.25–0.45 | 0.30–0.55 | 0.35–0.65 | Uncoated carbide + sharp edge |
Safety note: When drilling magnesium, ensure chips do not accumulate in contact with water-based coolants, as fine magnesium chips can react exothermically. Use oil-based coolant or dedicated magnesium machining fluid.
ISO S — Superalloys and Titanium (Inconel, Hastelloy, Ti-6Al-4V)
Superalloys and titanium alloys are among the most difficult materials to drill due to their high strength at elevated temperatures, low thermal conductivity, and severe work-hardening tendency. Cutting speeds are low, and tool life is typically the limiting factor.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Titanium Ti-6Al-4V (annealed) | 280–330 HB | 20–40 | 0.06–0.12 | 0.08–0.16 | 0.12–0.22 | AlTiN PVD ultra-fine grain |
| Titanium Ti-6Al-4V (solution treated) | 320–380 HB | 15–30 | 0.05–0.10 | 0.07–0.14 | 0.10–0.18 | TiAlN + TiCN multi-layer PVD |
| Inconel 718 (solution treated) | 280–360 HB | 15–25 | 0.05–0.10 | 0.07–0.12 | 0.10–0.16 | AlTiN PVD tough substrate |
| Inconel 718 (aged) | 380–450 HB | 10–18 | 0.04–0.08 | 0.06–0.10 | 0.08–0.14 | Ceramic (Si3N4) or AlTiN PVD |
| Hastelloy X / C276 | 200–280 HB | 12–22 | 0.05–0.10 | 0.07–0.14 | 0.10–0.18 | AlTiN PVD fine-grain carbide |
| Waspaloy / Rene 41 | 300–420 HB | 8–15 | 0.04–0.08 | 0.05–0.10 | 0.08–0.14 | CBN-tipped or whisker-reinforced ceramic |
Critical note for titanium: Never use uncoated carbide or TiN-coated grades for titanium drilling — titanium has a chemical affinity for titanium nitride at cutting temperatures, causing severe BUE and crater wear. AlTiN with high aluminum content is the minimum recommended coating.
ISO H — Hardened Steel (45–65 HRC)
Drilling hardened steel with indexable inserts requires specialized tooling and conservative parameters. For most applications, solid carbide or CBN-tipped drills are preferred, but indexable drills can be used for short-run production with appropriate grade selection.
| Material Subtype | Hardness | Vc (m/min) | fn D10–20 (mm/rev) | fn D20–40 (mm/rev) | fn D40–80 (mm/rev) | Recommended Grade/Coating |
|---|---|---|---|---|---|---|
| Hardened steel (45–50 HRC) | 45–50 HRC | 30–50 | 0.05–0.10 | 0.07–0.14 | 0.10–0.18 | CBN-tipped inserts |
| Hardened steel (50–55 HRC) | 50–55 HRC | 20–35 | 0.04–0.08 | 0.06–0.12 | 0.08–0.15 | CBN-tipped, low CBN content |
| Hardened steel (55–60 HRC) | 55–60 HRC | 12–25 | 0.03–0.06 | 0.05–0.09 | 0.07–0.12 | CBN-tipped, high CBN content |
| Hardened steel (60–65 HRC) | 60–65 HRC | 8–15 | 0.02–0.05 | 0.04–0.07 | 0.06–0.10 | PCBN with ceramic binder |
Important: For hardened steel above 55 HRC, indexable drills with CBN inserts are generally limited to shallow holes (≤ 2×D). For deeper holes, consider a pre-drill + finish-bore strategy or use solid carbide drills with special geometry.
Grade Selection Quick Reference
Choosing the right carbide grade and coating is as important as selecting the correct cutting parameters. The table below summarizes grade recommendations by material group for indexable drill inserts.
| ISO Group | Primary Grade Type | Coating | Coating Thickness | Grain Size | Typical Failure Mode |
|---|---|---|---|---|---|
| P (Steel) | CVD-coated carbide | TiCN/Al2O3/TiN | 8–12 µm | Medium (1–2 µm) | Flank wear, crater wear |
| M (Stainless) | PVD-coated carbide | AlTiN / TiAlN | 2–4 µm | Fine (0.5–1 µm) | BUE, notch wear |
| K (Cast Iron) | CVD-coated carbide | TiCN/Al2O3 | 6–10 µm | Medium (1–2 µm) | Abrasive wear |
| N (Non-ferrous) | Uncoated or DLC | DLC / PCD | 1–3 µm / 0.5 mm | Ultra-fine | BUE, adhesion |
| S (Superalloy) | PVD-coated carbide | AlTiN (high Al) | 2–5 µm | Ultra-fine (<0.5 µm) | Notch wear, thermal cracking |
| H (Hardened) | CBN / PCBN | Uncoated or TiN | — | Micro-grain | Chipping, flank wear |
Parameter Adjustment Guidelines
Depth-to-Diameter Ratio (L/D) Adjustments
The parameters in the tables above assume a 2–3×D drilling depth. For deeper holes, adjust parameters as follows:
- 4×D: Reduce feed rate by 10–15%. Maintain cutting speed.
- 5×D: Reduce feed rate by 20–25%. Reduce Vc by 5–10%.
- 6–8×D: Reduce feed rate by 30–40%. Reduce Vc by 15–20%. Use peck drilling cycle.
Coolant Pressure and Flow Requirements
| Drill Diameter | Min Coolant Pressure (bar) | Min Coolant Flow (L/min) | Coolant Type |
|---|---|---|---|
| Ø10–20 mm | 10–15 | 8–15 | Emulsion 5–8% |
| Ø20–40 mm | 15–25 | 15–30 | Emulsion 7–10% |
| Ø40–80 mm | 20–30 | 30–60 | Emulsion 8–12% |
| Ø80–120 mm | 25–40 | 50–100 | Emulsion 10–15% |
Peck Drilling Recommendations
For deep holes (L/D > 4×), peck drilling cycles improve chip evacuation and reduce tool deflection. Recommended peck depths:
- First peck: 1.5–2×D
- Subsequent pecks: 0.5–1×D
- Retraction: Full retraction out of the hole every 3–5 pecks for complete chip clearing
Common Drilling Problems and Solutions
| Problem | Possible Cause | Solution |
|---|---|---|
| Rapid flank wear | Vc too high; grade too soft; abrasive material | Reduce Vc by 15–20%; switch to more wear-resistant grade; increase coolant pressure |
| Built-up edge (BUE) | Feed too low; coating not suitable; poor coolant | Increase fn by 20%; use AlTiN or DLC coating; increase coolant concentration |
| Insert chipping | Feed too high; unstable setup; interrupted cut | Reduce fn by 15–25%; improve rigidity; reduce feed at entry/exit |
| Poor hole quality (rough surface) | Feed too high; tool deflection; worn insert | Reduce fn; check alignment and runout; replace inserts |
| Oversized holes | Worn outer insert; spindle runout; drill body deflection | Replace outer insert; check spindle TIR; reduce overhang |
| Drill breakage | Chip packing; feed too high; misalignment; low coolant pressure | Implement peck cycle; reduce fn; align workpiece; increase coolant flow |
| Severe chatter | Unstable setup; long overhang; unfavorable fn | Shorten tool overhang; increase rigidity; adjust fn up or down 20% |
Competitive Technology Comparison
Leading cutting tool manufacturers each take a slightly different approach to indexable drill design. Understanding these differences helps in selecting the right tool for your specific application.
| Feature | Sandvik CoroDrill 880 | Iscar Sumocham | Kennametal KSEM | Walter Xtra·tec |
|---|---|---|---|---|
| Insert shape | Square with 4 cutting edges | Trigon with 3 cutting edges | Square with 4 cutting edges | Square with 4 cutting edges |
| Central insert geometry | Self-centering point | Helical geometry | Flat-bottom design | Chamfered edge |
| Standard L/D ratios | 2×, 3×, 4×, 5×, 8× | 1.5×, 3×, 5×, 7×, 10× | 2×, 3×, 5×, 7×, 10× | 2×, 3×, 4×, 5×, 7× |
| Diameter range | 12–110 mm | 12–120 mm | 12–130 mm | 13–110 mm |
| Coolant supply | 2 coolant holes | 2–4 coolant holes | 2 coolant holes | 2 coolant holes + front jet |
| Steel (P) Vc range | 100–180 m/min | 100–200 m/min | 90–160 m/min | 95–170 m/min |
| Stainless (M) Vc range | 60–100 m/min | 55–110 m/min | 50–95 m/min | 55–100 m/min |
| Best known for | High precision hole quality | High feed rates and productivity | Versatility across materials | Stability in interrupted cuts |
Conclusion
Indexable insert drills offer exceptional productivity and cost efficiency for a wide range of drilling applications across all ISO material groups. The key to success lies in matching cutting parameters (Vc, fn) and tooling (grade, coating, geometry) to the specific workpiece material and machine capability.
As a general rule of thumb, start at the lower end of the recommended parameter ranges and increase gradually while monitoring tool wear, chip formation, and hole quality. Always prioritize feed rate increases over speed increases for improving productivity, as higher feed rates generally have a less negative impact on tool life than excessive cutting speeds.
Keep this reference guide handy as a starting point for your indexable drilling operations, and always consult the tool manufacturer’s specific recommendations for the exact drill body and insert grade you are using.
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