Introduction: Two Drill Specialists Compared
Among global cutting-tool manufacturers, few wear the “drill specialist” label as convincingly as Nachi-Fujikoshi and OSG Corporation. Both Japanese houses built their reputations on hole-making rather than spreading thin across every turning and milling niche. Their solid carbide drill portfolios therefore represent a concentrated, engineering-led approach in which point geometry, helix design, substrate, and coating are developed together as a single system. This comparison breaks down how Nachi and OSG approach each of those variables and translates them into concrete cutting parameters for the materials you actually run on the shop floor.
Where the two brands diverge most visibly is in their coating philosophy and their point-edge geometry. Nachi leans on its AZ coating family — an AlCrN-based nano-multilayer architecture tuned for high hardness and thermal stability — while OSG’s flagship ADO and EXOPRO lines run the EXO / WLA coating family, an AlTiCrN multilayer optimized for lubricant adhesion and chip evacuation. Below we examine what each choice means for tool life, surface finish, and the speeds and feeds you can safely push.
1. Solid Carbide Drill Portfolios at a Glance
Nachi — the Aqua Solid Carbide Drill family
Nachi’s modern solid carbide drill offering is consolidated under the Aqua banner, a name that signals the line’s compatibility with both emulsion and through-coolant operation. Key variants include:
- Aqua Solid Carbide Drill (general / steel) — 3-5xD and 8xD bodies, 130° point, for ISO P and K materials.
- Aqua Solid Carbide Drill for Stainless — refined margin and edge-hone for ISO M workhardening alloys.
- Aqua Solid Carbide Drill for Hardened Steel — heavier web, tougher substrate, for workpieces up to roughly HRC 55.
- Aqua Micro Drill — small-diameter (sub-3 mm) geometry with reinforced core for micro-hole stability.
OSG — the ADO / EXOPRO drill family
OSG segments its solid carbide drills primarily by application and coating rather than by a single umbrella name:
- ADO series — the workhorse general-purpose carbide drill, coated with the EXO multilayer (AlTiCrN), available in 3-5xD, 8xD, and extended lengths.
- WDO series — engineered for stainless steel and water-soluble coolant, with a polished flute and a coating that resists galling.
- EXOPRO series (GOLD / S-GOLD / V-PH) — premium tier carrying the WLA/WLS AlCrN-based coatings, targeting difficult-to-machine alloys and high-speed production.
- ADO-Micro — micro-diameter platform with a self-centering point for stable entry on small holes.
2. Point Geometry and Edge Architecture
The drill point is where thrust force, hole roundness, and chip formation are decided. Both brands move away from the legacy 118° conical point toward steeper, self-centering geometries, but they execute it differently.
| Geometry feature | Nachi (Aqua family) | OSG (ADO / EXOPRO) |
|---|---|---|
| Standard point angle | 130° (S-point / split point) | 130° – 140° (X-point / 4-facet split) |
| Self-centering design | Split point with thinned web (XR-style) | 4-facet / notched point with reduced chisel |
| Chisel-edge reduction | ~50% of core web | ~40-55% via two-stage thinning |
| Helix angle (general) | 30° (standard), 28° for hardened | 30° (standard), 38° for aluminum variants |
| Margin design | Single/double margin by length ratio | Double margin on 8xD+ for hole tolerance |
| Edge hone | Light hone for steel, heavier for hard/cast | Tapered hone, larger land for stainless |
The practical consequence: Nachi’s split-point geometry tends to produce slightly lower entry thrust on steels, making it forgiving on less-rigid setups or angled entry surfaces. OSG’s 4-facet point excels at hole roundness and diameter stability in longer 8xD and deeper bodies, where margin support and a well-thinned chisel keep the drill from wandering. For hardened steel above HRC 50, both brands steepen the point to 135°-140° and add a more substantial web to resist torsional fracture — a common failure mode when drill bodies are too thin and the chip load spikes.
3. Coating Technology: AZ vs EXO / WLA
Coating is the single largest differentiator between the two portfolios. The table below summarizes the technical parameters of the principal coating families.
| Coating property | Nachi AZ coating | OSG EXO (AlTiCrN) | OSG WLA (AlCrN) |
|---|---|---|---|
| Base chemistry | AlCrN nano-multilayer | AlTiCrN multilayer | AlCrN-based multilayer |
| Nano-hardness | ~3300 HV | ~3000-3200 HV | ~3200-3400 HV |
| Oxidation temp. | ~1100°C | ~900-1000°C | ~1000-1100°C |
| Friction coeff. | ~0.35 | ~0.40 | ~0.35 |
| Coating color | Black-violet | Dark gold / bronze | Light gold |
| Best fit | Hardened steel, cast iron, high-temp | General steel, alloy steel, dry-cut | Stainless, titanium, high-speed |
Several engineering principles explain the differences. AlCrN chemistry (Nachi AZ, OSG WLA) achieves higher oxidation resistance than AlTiN-family films because chromium forms a stable protective oxide scale at the coating surface, delaying breakdown at the elevated cutting temperatures reached in high-speed drilling. The nano-multilayer architecture periodically interrupts columnar grain growth, which raises hardness and fracture toughness simultaneously — useful when chips rub against the flute under intermittent coolant supply.
OSG’s EXO coating stays with an AlTiCrN base for its general-purpose line because the titanium-rich surface retains excellent adherence to emulsion-based coolants and resists adhesive wear on low-alloy steels that produce long, ductile chips. For stainless and titanium, where built-up edge and galling dominate, OSG switches to the WLA AlCrN family with a smoother, lower-friction surface that discourages weld-on of workpiece material.
Flute surface treatment
Both brands polish the flute landings behind the cutting edge. Nachi’s Aqua line uses a bright, low-roughness flute to accelerate chip transport and reduce the risk of chip packing in deep-hole bodies. OSG’s WDO and EXOPRO lines take polishing further with a near-mirror land, explicitly to defeat the galling chip that stainless steel (notably 316L and 304) produces when it workhardens at the cutting edge.
4. Substrate and Body Design
The carbide substrate determines how much toughness the drill body sacrifices for wear resistance. Both manufacturers use ultra-fine to sub-micron cobalt-binder tungsten carbide, but they tune the grain size and cobalt content per application.
- Nachi favors a slightly finer grain (sub-0.5 µm) with ~6% cobalt for the Aqua hardened-steel variants, trading a small amount of toughness for edge retention at high cutting temperature. The hardened-steel drill adds a thicker core web and a shorter flute length-to-diameter ratio to resist torsional buckling.
- OSG runs a ~0.5-0.6 µm grain with 6-8% cobalt depending on series. The ADO uses a balanced substrate; the EXOPRO hardened-steel and high-temp variants step up cobalt content and add a back-tapered body that relieves friction on the margins in deep holes.
| Body parameter | Nachi Aqua (3xD) | OSG ADO (3xD) |
|---|---|---|
| Web thickness (% of dia.) | ~45-50% | ~42-48% |
| Back taper (mm/dia.) | ~0.02-0.04 | ~0.02-0.05 |
| Flute profile | Wide, low-rake for chip room | Slightly deeper, polished land |
| Core taper | Stepped (thicker toward shank) | Stepped (thicker toward shank) |
5. Cutting Parameters by Material Class
The values below are representative starting parameters for solid carbide drills of approximately 6-10 mm diameter in 3-5xD configuration, run with through-tool coolant at 5-8% emulsion concentration. They should be treated as baseline recommendations to be validated on your specific machine rigidity and workpiece condition. Parameters marked “HRC” refer to the workpiece hardness of the listed material class.
ISO P — Carbon and Alloy Steels
| Steel condition | Nachi Aqua (Vc, m/min) | OSG ADO (Vc, m/min) | Feed fn (mm/rev) | Peck depth (ap) |
|---|---|---|---|---|
| Low-carbon steel (<200 HB) | 80-110 | 70-100 | 0.10-0.20 | 1.5xD continuous |
| Alloy steel (250-320 HB) | 60-85 | 55-80 | 0.08-0.16 | 1.0xD peck on 5xD |
| Quenched steel (HRC 35-45) | 40-55 | 35-50 | 0.06-0.12 | 0.5-0.8xD peck |
Both drills handle low-carbon steel comfortably at the upper end of the range. Nachi’s AZ coating tends to sustain higher Vc on alloy steels because its higher oxidation temperature tolerates the heat spike when feed is increased to break a long stringy chip. OSG’s EXO, with its stronger coolant adhesion, is a touch more conservative in Vc but very stable on rigid setups.
ISO M — Stainless Steels
| Stainless type | Nachi Aqua-Stainless (Vc) | OSG WDO (Vc) | Feed fn (mm/rev) | Peck strategy |
|---|---|---|---|---|
| 304 / 316L (austenitic) | 45-65 | 40-60 | 0.05-0.14 | 0.3-0.5xD peck, 5xD body |
| Duplex 2205 | 30-45 | 28-42 | 0.05-0.10 | 0.25-0.4xD peck |
| Precipitation hardening (17-4 PH) | 35-50 | 30-45 | 0.05-0.12 | 0.3-0.5xD peck |
Stainless drilling is where the brand philosophies clash most directly. Workhardening at the cutting edge raises the effective hardness of the chip zone by 30-50%, so the coating must resist adhesive buildup while the flute must clear the tough chip. OSG’s polished-flute WDO is engineered specifically for this regime — its lower friction surface and emulsion-friendly coating reduce galling on 316L. Nachi’s stainless Aqua variant relies on a heavier edge hone and a wider chip room to keep the workhardened chip moving, accepting slightly lower Vc in exchange for chip-transport reliability on deep holes.
ISO K — Cast Iron
| Cast iron grade | Nachi Aqua (Vc) | OSG ADO (Vc) | Feed fn (mm/rev) | Coolant |
|---|---|---|---|---|
| Grey iron (200 HB) | 90-130 | 80-120 | 0.12-0.25 | Emulsion / air |
| Nodular (ductile) iron | 70-100 | 60-90 | 0.10-0.20 | Emulsion |
| Compacted graphite (CGI) | 50-75 | 45-70 | 0.08-0.16 | Emulsion, high pressure |
Cast iron produces a short, abrasive chip that erodes the cutting edge through micro-chipping rather than gross fracture. The higher Vc that Nachi’s AZ coating sustains is advantageous here because it keeps the cutting temperature above the range where the free graphite smears and glazes the edge. For CGI, the higher strength and lower machinability demand both brands drop to the lower Vc band and increase peck frequency to prevent chip re-cutting.
ISO H — Hardened Steel (HRC 50-62)
| Hardness | Nachi Aqua-Hardened (Vc) | OSG EXOPRO hardened (Vc) | Feed fn (mm/rev) | Peck (ap) |
|---|---|---|---|---|
| HRC 50-55 | 35-50 | 30-45 | 0.05-0.10 | 0.25-0.4xD |
| HRC 55-60 | 25-38 | 22-35 | 0.04-0.08 | 0.2-0.3xD |
| HRC 60-62 | 18-28 | 15-25 | 0.03-0.06 | 0.15-0.25xD |
Hardened-steel drilling is the most demanding regime for a solid carbide drill. The cutting edge runs at the boundary between plastic and brittle removal of the workpiece, and the chip is small, hot, and abrasive. Both brands restrict the depth-of-cut (peck depth) aggressively and recommend high-pressure through-coolant (70 bar and above) to evacuate heat. Nachi’s finer-grain substrate and AZ coating give it a small but consistent Vc advantage in the upper hardness bands; OSG compensates with a more compliant body taper and a tougher cobalt-rich substrate that resists the shock of re-entry after pecking.
6. Application-Based Selection Guidance
- High-mix low-volume, mixed steel grades: OSG ADO with EXO coating — its coolant adhesion and balanced substrate make it the most forgiving general-purpose choice when material condition varies.
- Stainless 316L / duplex production: OSG WDO with polished flute and AlCrN — purpose-built for the workhardening and galling that defeat general-purpose drills.
- Cast iron at elevated Vc: Nachi Aqua general with AZ coating — higher oxidation temperature sustains the speeds that keep the edge out of the graphite-smearing zone.
- Hardened steel HRC 55-60: Nachi Aqua-Hardened on rigid machines; OSG EXOPRO hardened where peck-re-entry shock is the dominant failure mode.
- Deep holes 8xD and beyond: Either brand’s 8xD body, but prioritize the one with through-coolant and the double-margin option — hole tolerance and chip evacuation matter more than coating chemistry at these length ratios.
7. Failure Modes and How Each Brand Addresses Them
| Failure mode | Root cause | Nachi countermeasure | OSG countermeasure |
|---|---|---|---|
| Edge chipping | Shock load, interrupted cut | Heavier hone, tougher substrate | Compliant back taper, larger cobalt |
| Flute packing | Chip too long / no room | Wide low-rake flute, bright polish | Deep polished land, peck cycle |
| Built-up edge | Adhesion (stainless, titanium) | Smooth low-friction AZ surface | WLA AlCrN, polished WDO flute |
| Gross fracture | Torsional overload in deep body | Thick stepped core web | Thicker web on 8xD, relieved margin |
| Thermal cracking | Intermittent coolant supply | High oxidation-temp coating | Through-coolant body design |
Conclusion
Nachi and OSG approach solid carbide drilling from different but equally valid starting points. Nachi’s engineering favors the coating-thermal axis: a fine-grain substrate paired with the AZ AlCrN nano-multilayer that tolerates higher cutting temperature, which translates into a consistent Vc advantage on cast iron, hardened steel, and high-temperature alloys where heat is the limiting factor. OSG’s engineering favors the chip-evacuation-adhesion axis: the EXO and WLA coating families, polished flutes, and compliant body geometry are tuned to keep difficult chips moving on stainless steel and to preserve hole quality in deep bodies.
For a shop that drills predominantly low-alloy steels and cast iron and pushes for cycle-time reduction, the Nachi Aqua line will typically deliver a small speed advantage. For a shop that lives in stainless steel, duplex, and deep-hole bodies where galling and chip packing are the daily killers, the OSG WDO and EXOPRO families are the more purpose-built answer. In hardened steel the two converge — both restrict peck depth and demand high-pressure coolant, and the choice is more often decided by machine rigidity and peck-strategy control than by the coating on the flute.
