Austenitic stainless steels 304 and 316 are among the most challenging materials for deep hole drilling. Their high ductility, rapid work-hardening rate, and tendency to produce long stringy chips create conditions that punish incorrect parameters immediately — tool breakage, catastrophic work hardening, and scrapped parts are common when these materials are approached with parameters intended for carbon steel.
Yet 304 and 316 are also among the most frequently specified materials for deep hole drilled components: chemical processing equipment, pharmaceutical machinery, marine hardware, heat exchangers, and food-grade piping all require the corrosion resistance that only stainless steel provides. Learning to deep hole drill these materials reliably is a valuable capability.
This guide covers the complete range of cutting data for deep hole drilling 304 and 316 stainless steel, with manufacturer-sourced parameters, coolant requirements, and specific strategies for managing work hardening and chip evacuation.
Material Comparison: 304 vs 316
Both 304 and 316 are austenitic stainless steels, but their differences in composition and behavior have significant implications for deep hole drilling.
Chemical Composition
| Element | 304 (18/8) | 316 |
|---|---|---|
| Chromium | 18–20% | 16–18% |
| Nickel | 8–10.5% | 10–14% |
| Molybdenum | None | 2–3% |
| Carbon | ≤ 0.08% | ≤ 0.08% |
| Manganese | ≤ 2% | ≤ 2% |
The addition of molybdenum in 316 is what gives it superior corrosion resistance in chloride environments — but it also increases the work-hardening rate and makes drilling more difficult.
Mechanical Properties
| Property | 304 | 316 |
|---|---|---|
| Tensile strength (min) | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
| Yield strength (0.2%) | 205 MPa (30 ksi) | 205–220 MPa (30–32 ksi) |
| Elongation | 40–60% | 40–60% |
| Hardness (Brinell) | ≤ 201 HB | ≤ 183–201 HB |
| Hardness (Rockwell B) | 70–90 HRB | 75–95 HRB |
| Work-hardening rate | Moderate | 15% higher than 304 |
Machinability Comparison
| Factor | 304 | 316 |
|---|---|---|
| Relative machinability | Baseline | ~85% of 304 |
| Cutting speed (carbide) | 80–130 SFM | 70–120 SFM |
| Work hardening tendency | Moderate | Higher — more aggressive parameter management needed |
| Tool life expectation | Better | ~20–30% shorter than 304 at equivalent speeds |
| Recommended feed range | 0.003–0.012 IPR | 0.003–0.010 IPR |
| Coolant pressure requirement | ≥ 70 bar (1,000 PSI) | ≥ 70 bar (1,000 PSI) |
The key difference: 316 has a 15% higher work-hardening rate than 304. This means it hardens more during cold working, including during the cutting process. If the feed rate is too low or the tool is dull, the material hardens ahead of the cutting edge, making each subsequent pass more difficult than the last. This is the primary reason 316 requires more conservative speeds and more consistent feed than 304.
Cutting Parameters for Gun Drilling
The following tables compile data from Allied Machine, Mitsubishi Carbide, BSSA (British Stainless Steel Association), and published research specific to 300-series austenitic stainless steel.
Carbide-Tipped Gun Drills — 304 Stainless Steel
| Diameter (mm) | Diameter (inch) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|---|
| 3–5 | 0.118–0.197 | 130–260 | 40–80 | 0.003–0.006 | 0.08–0.15 |
| 5–8 | 0.197–0.315 | 195–260 | 60–80 | 0.004–0.008 | 0.10–0.20 |
| 8–12 | 0.315–0.472 | 150–230 | 46–70 | 0.006–0.009 | 0.15–0.23 |
| 12–16 | 0.472–0.630 | 150–230 | 46–70 | 0.007–0.010 | 0.18–0.25 |
| 16–20 | 0.630–0.787 | 130–195 | 40–60 | 0.007–0.011 | 0.18–0.28 |
| 20–30 | 0.787–1.181 | 130–195 | 40–60 | 0.008–0.012 | 0.20–0.30 |
Based on Mitsubishi MMS data and Allied Machine T-A values for 300-series stainless (185–275 BHN). Use the lower end of the speed range for 316 and the upper end for 304.
Carbide-Tipped Gun Drills — 316 Stainless Steel
| Diameter (mm) | Speed (SFM) | Speed (m/min) | Feed (IPR) | Feed (mm/rev) |
|---|---|---|---|---|
| 3–5 | 100–195 | 30–60 | 0.003–0.005 | 0.08–0.13 |
| 5–8 | 150–200 | 46–61 | 0.004–0.007 | 0.10–0.18 |
| 8–12 | 130–195 | 40–60 | 0.005–0.008 | 0.13–0.20 |
| 12–16 | 130–195 | 40–60 | 0.006–0.009 | 0.15–0.23 |
| 16–20 | 115–165 | 35–50 | 0.006–0.010 | 0.15–0.25 |
| 20–30 | 100–165 | 30–50 | 0.007–0.010 | 0.18–0.25 |
Reduce speed by approximately 15% from 304 values for 316. Feed rates are similar at the lower end but should not exceed approximately 85% of 304’s maximum feed at equivalent diameter.
By Hardness — Allied Machine T-A System Data (300-Series Stainless)
| Hardness (BHN) | Speed (SFM) | Feed (IPR) by Series (Diameter Range) |
|---|---|---|
| 135–185 BHN (annealed) | 160–210 | Y/Z: 0.006; 0: 0.007; 1: 0.009; 2: 0.010; 3: 0.012 |
| 185–275 BHN (work-hardened) | 120–160 | Y/Z: 0.004; 0: 0.006; 1: 0.008; 2: 0.009; 3: 0.010 |
Series Y/Z: 0.374–0.500“ (9.5–12.7 mm); Series 0: 0.500–0.695“ (12.7–17.7 mm); Series 1: 0.695–0.960“ (17.7–24.4 mm); Series 2: 0.960–1.380“ (24.4–35.1 mm); Series 3: 1.380–1.882“ (35.1–47.8 mm)
Important note: The upper hardness range (185–275 BHN) represents a work-hardened condition. 304 and 316 in their annealed state typically fall at 135–185 BHN. If there is any doubt about the material condition, start at the 185–275 values — this is safer because austenitic stainless steel work-hardens rapidly during drilling if parameters are not optimal.
Cutting Parameters for BTA Drilling
BTA drilling of stainless steel requires reduced parameters compared to carbon steel at equivalent diameters, primarily due to the higher cutting forces and work-hardening tendency.
BTA — 304/316 Stainless Steel (Carbide Inserts)
| Diameter (mm) | Speed (SFM) | Feed (mm/rev) | Coolant Pressure |
|---|---|---|---|
| 12–20 | 120–200 | 0.12–0.22 | 200–330 PSI (14–23 bar) |
| 20–30 | 100–180 | 0.15–0.26 | 190–260 PSI (13–18 bar) |
| 30–40 | 90–160 | 0.18–0.28 | 190–250 PSI (13–17 bar) |
| 40–50 | 80–140 | 0.20–0.30 | 190–240 PSI (13–17 bar) |
Allied Machine published data for 300-series stainless with the T-A system specifies coolant pressures of 190–329 PSI depending on diameter, with flow rates of 3–20 GPM.
BTA Case Study — 316 Stainless Steel
A documented deep hole drilling operation in 316 stainless steel (from industry reporting) used the following parameters for a 19 mm diameter hole at 200 mm depth:
- Cutting speed: 30 m/min (98 SFM)
- Feed rate: 0.05–0.15 mm/rev (0.002–0.006 IPR)
- Coolant pressure: 70 bar minimum
- Tool material: Coated carbide
- Result: Successful deep hole drilling with controlled tool wear
This case illustrates the conservative approach required for 316 — cutting speeds well below what carbon steel would allow, with high coolant pressure as the enabling factor.
Coolant Pressure Requirements
Coolant is the single most critical variable in deep hole drilling of austenitic stainless steel. More tools break from inadequate coolant than from incorrect speeds or feeds.
Minimum Pressure Guidelines
| Hole Depth (×D) | Minimum Coolant Pressure | Notes |
|---|---|---|
| Up to 5×D | 300 PSI (21 bar) | External coolant may be adequate for very short holes |
| 5×D to 10×D | 1,000 PSI (70 bar) | Internal through-tool coolant required |
| 10×D to 20×D | 1,000–1,500 PSI (70–100 bar) | Gun drilling standard pressure range |
| Over 20×D | 1,500+ PSI (100+ bar) | Specialized high-pressure system |
Why coolant pressure is more critical for stainless than for carbon steel:
- Heat removal: Austenitic stainless steel has approximately one-third the thermal conductivity of carbon steel. Heat generated at the cutting edge stays at the cutting edge. Without high-pressure coolant, the tool tip temperature rises rapidly, accelerating flank wear and promoting BUE.
- Chip evacuation: Stainless steel chips are tougher and more cohesive than carbon steel chips. They require higher coolant velocity to transport through the flute or evacuation tube.
- Work hardening prevention: Inadequate coolant allows chips to pack and rub against the bore wall, generating friction heat that work-hardens the material ahead of the tool.
Coolant type: For deep hole drilling of 304 and 316, use either:
- Low-viscosity cutting oil (best lubricity, preferred for gun drilling)
- High-performance emulsion at 8–12% concentration (acceptable for BTA drilling; must have adequate EP additive content)
Work Hardening — The Primary Challenge
Austenitic stainless steels work-harden at a rate approximately 2–3 times higher than carbon steel. This means that any condition that causes the tool to rub rather than shear — insufficient feed, a dull cutting edge, or dwell at the bottom of a peck cycle — will create a hardened zone that the tool must then cut through, causing accelerated wear and potentially tool breakage.
How Work Hardening Develops in Deep Hole Drilling
- The feed rate drops below the threshold needed for clean shearing (typically below 0.03 mm/rev for carbide)
- The cutting edge pushes material aside rather than shearing it
- The material undergoes plastic deformation, which work-hardens the surface layer
- Hardness in the affected zone can increase by over 100%, exceeding 500 HV
- On the next tool engagement, the cutting edge encounters this harder surface
- Edge chipping or breakage occurs, or the tool deflects, producing a out-of-straightness hole
Prevention Strategies
- Maintain minimum feed rate: Never allow feed to drop below 0.03 mm/rev (0.0012 IPR) for carbide tools in austenitic stainless steel. The ideal feed is 0.05–0.15 mm/rev.
- Never dwell: Do not stop the feed while the tool is cutting. If the spindle is rotating and the tool is in contact with the workpiece, it must be feeding.
- Use sharp tools: A dull tool increases the cutting force and promotes rubbing. Replace or regrind tools at the first sign of increased cutting pressure.
- Maintain constant chip load: Inconsistent feed (from machine acceleration/deceleration at the start of a cut) can create localized work-hardened spots.
If Work Hardening Occurs
If the tool stalls or cutting pressure rises suddenly:
- Stop the spindle immediately — do not attempt to power through
- Retract the tool
- Inspect the cutting edge for damage
- If the edge is intact and the hole is not fully hardened, reduce speed by 20% and increase feed by 10% before re-entering
- If the hole has fully hardened, it may not be possible to resume drilling — the hardened zone must be removed with a grinding or boring operation
Chip Breaking and Evacuation
Austenitic stainless steel produces tough, ductile chips that resist breaking. This is the second major challenge after work hardening.
Chip Breaking Strategies
| Method | How It Works | Best For |
|---|---|---|
| Increase feed rate | Thicker chips bend to a smaller radius and break more readily | Production, when machine power allows |
| Chip breaker geometry | Ground-in step on the rake face forces chip to curl and break | Gun drilling, BTA drilling |
| High coolant pressure | Flushes chips before they can pack; prevents chip congestion | All deep hole drilling |
| Peck drilling (with caution) | Retract to break long chips | HSS tools; avoid with carbide if possible |
For gun drilling: The chip breaker geometry on the gun drill tip is the primary chip control mechanism. Verify that the chip breaker is appropriate for stainless steel — general-purpose geometries designed for carbon steel may not produce adequate chip breaking in austenitic stainless.
For BTA drilling: The chip former in the drill head must be designed for ductile materials. Standard chip formers for cast iron or low-carbon steel will not break stainless steel chips effectively.
Chip analysis guide:
| Chip appearance | Indication | Action |
|---|---|---|
| Short, regular “C” or “6” shapes | Optimal parameters | Maintain current settings |
| Long, stringy ribbons | Feed too low or chip breaker inadequate | Increase feed 10–20% |
| Powder or dust | Speed too high or tool dull | Reduce speed, inspect tool |
| Needle-like chips | Built-up edge forming | Increase speed, check coolant lubricity |
Tool Selection
Carbide Grade
| Material | ISO Grade | Coating | Edge Preparation |
|---|---|---|---|
| 304 stainless (general) | K15–K25 | TiAlN or AlTiN (PVD) | Light hone, 0.01–0.03 mm |
| 304 (small diameters, <5mm) | K10–K20 | TiAlN or uncoated | Sharp edge |
| 316 stainless (general) | K20–K30 | TiAlN or AlTiN (PVD) | Honed edge, 0.03–0.05 mm |
| 316 (hardened or heavy cuts) | K25–K35 | CVD TiCN/Al₂O₃ | Honed edge, 0.05–0.08 mm |
TiAlN ( titanium aluminum nitride) is the standard coating for stainless steel. It provides thermal stability at the cutting interface and resists the adhesive wear that causes BUE.
Gun Drill Head Profile
- Profile E — Recommended for stainless steel. The E profile eliminates tool sticking in the hole after the outer corner dulls, a common problem in stainless steel deep hole drilling. Provides accurate hole straightness.
- Profile C — Use for stainless steel when interrupted cuts or angular entry conditions are present. Features increased back taper and larger coolant gaps.
- Profile G (Universal) — Acceptable for short holes in 304 but not recommended for 316 or deep holes exceeding 20×D in any austenitic stainless.
BTA Drill Head
For BTA drilling of stainless steel:
- Indexable insert heads with a tough carbide grade (K25–K35) and TiAlN coating
- Chip formers specifically designed for ductile materials
- Brazed carbide heads for diameters under 20 mm, with reduced clearance angles compared to cast iron grades
Depth Adjustment Factors
Apply the following adjustments for deep holes in stainless steel. These factors are based on BSSA guidelines and Allied Machine data, with additional reductions specific to austenitic stainless steel’s work-hardening behavior.
| Drilling Depth | Speed Factor | Feed Factor |
|---|---|---|
| Up to 3×D | 1.0 | 1.0 |
| 3×D to 5×D | 0.9 | 0.9 |
| 5×D to 8×D | 0.7 | 0.8 |
| 8×D to 12×D | 0.6 | 0.75 |
| 12×D to 20×D | 0.5 | 0.7 |
| Over 20×D | 0.4 | 0.6 |
For extended-length tool holders, apply additional reductions:
| Holder Length | Speed Factor | Feed Factor |
|---|---|---|
| Standard | 1.0 | 1.0 |
| Extended | 0.9 | 1.0 |
| Long | 0.85 | 0.95 |
| Extra Long (XL) | 0.80 | 0.90 |
| 3XL | 0.75 | 0.90 |
Deep Hole Drilling Procedure for 304/316
Pilot Hole
A properly prepared pilot hole is essential for stainless steel. The entry conditions determine whether the tool engages smoothly or immediately begins to work-harden the material.
- Depth: 1.5–2×D recommended (longer than for carbon steel)
- Diameter: 0.013–0.025 mm (0.0005–0.001“) larger than the deep hole drill
- Point angle: 135° split point — the split point reduces thrust force and prevents walking
- Surface prep: Spot face the entry surface to remove any scale or work-hardened layer. For small diameters, a light center drill mark instead of a conventional center punch prevents localized work hardening.
Entry Sequence
- Drill the pilot hole at 100% recommended speed and 100% feed — do not reduce feed at entry
- Feed the deep hole drill to within 1.5 mm of the pilot hole bottom at maximum 50 RPM with coolant OFF
- Turn coolant ON and allow it to stabilize (2–3 seconds)
- Begin feed at 50% speed and 75% feed for 1×D past the pilot hole bottom
- Increase to 100% speed and feed for the remainder of the hole
Running the Hole
- Peck drilling is not recommended with carbide gun drills or BTA tools in stainless steel. The interrupted cut causes thermal cycling and edge chipping.
- If pecking is unavoidable (limited coolant pressure, HSS tooling), use this sequence:
- First peck: 3–4×D deep
- Second peck: 2×D deep
- All subsequent pecks: 1×D deep
- Retract fully to clear chips
- Do not allow the tool to dwell at the bottom of the peck before retracting
- Monitor coolant pressure continuously — a sudden 10% drop indicates partial chip blockage
Breakout and Retract
- Through holes: Reduce speed by 50% and feed by 25% before breakout. The breakout burr in stainless steel is more pronounced than in carbon steel — plan for a deburring operation.
- Retract: Reduce speed to maximum 50 RPM before retracting, with coolant ON during retraction to flush remaining chips.
Surface Finish and Dimensional Accuracy
| Parameter | 304 (Gun Drilling) | 316 (Gun Drilling) | 304/316 (BTA Drilling) |
|---|---|---|---|
| Surface finish (Ra) | 0.4–1.6 µm | 0.4–0.8 µm (with optimized parameters) | 1.0–3.0 µm |
| Diameter tolerance | IT7–IT9 | IT7–IT9 | IT8–IT10 |
| Straightness (per 1,000 mm) | 0.05–0.3 mm | 0.05–0.3 mm | 0.1–0.5 mm |
316 can achieve a better surface finish than 304 under optimized conditions because its higher work-hardening rate produces a cleaner shear surface. A documented case of Φ2.5 mm × 40 mm deep gun drilling in 316L achieved Ra ≤ 0.8 µm without secondary operations and straightness below 0.02 mm.
Academic research on 304 stainless steel gun drilling found that the internal edge angle of the gun drill had a significant effect on surface roughness — increasing the internal edge angle improved hole wall surface finish. The same research found that increasing the external edge angle reduced straightness offset.
Common Problems
Tool Breakage on Entry
Symptom: The gun drill or BTA tool breaks within the first 5 mm of the hole.
Cause: Inadequate pilot hole, excessive entry speed, or a work-hardened surface layer.
Solution:
- Verify pilot hole depth (minimum 1.5×D) and diameter (+0.013–0.025 mm over drill diameter)
- Ensure the entry surface is spot-faced to remove any scale or hard layer
- Reduce entry speed to 50% of running speed for the first 2 mm
- Verify that the guide bush clearance is correct (+0.003 to +0.008 mm)
Chip Packing — 316
Symptom: Coolant pressure rises, then drops sharply. Torque increases. Tool stops cutting.
Cause: 316’s tougher chips pack in the flute or evacuation tube. This is more severe in 316 than 304 because the higher nickel content produces more ductile chips.
Solution:
- Increase coolant pressure — if running at 500 PSI, go to 1,000 PSI
- Reduce speed to lower the chip formation temperature (which increases chip ductility)
- Verify chip breaker geometry — consult the tool manufacturer for a stainless steel-specific chip breaker
- Consider switching to oil-based coolant for better lubricity
Built-Up Edge
Symptom: Rough bore surface, fluctuating torque, material adhered to the cutting edge.
Cause: Cutting speed too low for the material and tool combination. At low cutting speeds (below approximately 100 SFM), the chip material welds to the carbide tool.
Solution:
- Increase cutting speed if tool life allows — above 130 SFM for 304, above 100 SFM for 316
- Use TiAlN-coated tooling for better lubricity
- Ensure coolant concentration is adequate (8–12% for emulsion)
- Verify feed rate is not too low — feeds below 0.03 mm/rev increase BUE formation
Rapid Flank Wear
Symptom: Surface finish deteriorates after a few holes, cutting forces increase, tool must be reground prematurely.
Cause: 316’s molybdenum content creates abrasive wear on the carbide tool. The work-hardened chip also contributes to abrasive wear as it passes over the flank face.
Solution:
- Reduce cutting speed by 15–20% from the starting value
- Use a tougher carbide grade (K25–K35) with a thicker TiAlN coating
- Verify that the edge hone is adequate — insufficient edge preparation causes rapid flank wear in stainless steel
- Consider a CVD-coated grade for maximum abrasive wear resistance in high-volume production
Summary
Deep hole drilling 304 and 316 stainless steel requires a fundamentally different approach from carbon steel. The key principles:
- Control work hardening above all else — maintain minimum feed rate (0.03 mm/rev), never dwell, use sharp tools
- Coolant pressure of 1,000 PSI (70 bar) minimum for holes exceeding 5×D depth — this is not optional for reliable drilling
- Reduce speeds by 40–60% compared to carbon steel at equivalent diameter
- 316 requires an additional 15% speed reduction from 304 values, with particular attention to chip control
- Use TiAlN-coated carbide — uncoated tools and HSS tools have very limited life in austenitic stainless
- Continuous feed is preferred — peck drilling should be avoided with carbide in stainless steel
For related reading, see the Speeds and Feeds for Deep Hole Drilling Reference Tables, the Deep Hole Drilling Troubleshooting Guide, and the Tool Coatings for Deep Hole Drilling Guide.