Deep Hole Drilling Stainless Steel: Challenges and Parameters
Complete guide to deep hole drilling stainless steel — work hardening, chip breaking, tool selection, cutting parameters, and coolant strategies for austenitic, martensitic, and ferritic grades.
July 2, 2026 · Deep Hole Drilling Guide Team
Deep Hole Drilling Stainless Steel
Stainless steel is one of the most challenging material groups for deep hole drilling. Its work hardening tendency, low thermal conductivity, and stringy chip formation require careful parameter selection and robust tooling.
This guide covers deep hole drilling parameters, tool selection, and best practices for the major stainless steel grades.
Stainless Steel Grades Overview
Austenitic (300 Series)
The most common stainless steel family for deep hole drilling applications.
Grade
Typical Applications
Deep Hole Challenges
304
Food equipment, chemical processing
Work hardens quickly; stringy chips
316
Marine, medical, pharmaceutical
Higher work hardening than 304; built-up edge
321
Aerospace exhaust, heat exchangers
Titanium-stabilized — abrasive to tooling
347
High-temperature applications
Niobium-stabilized — very abrasive
Property
Impact on Deep Hole Drilling
Work hardening rate
High — the material surface hardens under the cutting edge, making subsequent passes difficult
Thermal conductivity
Low (16 W/m·K vs 50+ for carbon steel) — heat concentrates at the cutting edge
Tensile strength
Moderate (500–700 MPa) but high ductility — produces stringy chips
Carbide affinity
High — tendency to form built-up edge (BUE)
Martensitic (400 Series)
Grade
Typical Applications
Deep Hole Drilling
410
Valves, pumps, shafts
Easier than austenitic — less work hardening
416
Free-machining stainless
Best stainless for deep hole drilling (sulfur content improves chip breaking)
420
Cutlery, surgical instruments
Harder — requires reduced speeds
Ferritic (430 Series)
Grade
Typical Applications
430
Automotive trim, appliances
Cutting Parameters
Gun Drilling — Austenitic Stainless
Diameter
Speed (m/min)
Feed (mm/rev)
Coolant Pressure (bar)
3–6 mm
50–65
0.008–0.015
70–100
6–12 mm
55–70
0.015–0.030
50–80
12–20 mm
55–75
0.025–0.045
40–60
20–30 mm
50–70
0.035–0.055
35–50
BTA Drilling — Austenitic Stainless
Diameter
Speed (m/min)
Feed (mm/rev)
Coolant Pressure (bar)
20–40 mm
50–70
0.10–0.20
40–60
40–65 mm
45–65
0.15–0.25
35–50
65–100 mm
40–60
0.18–0.30
30–45
Gun Drilling — Martensitic (Free-Machining 416)
Diameter
Speed (m/min)
Feed (mm/rev)
3–12 mm
70–100
0.015–0.040
12–25 mm
65–90
0.030–0.060
Ejector Drilling — Austenitic Stainless
On a retrofitted CNC lathe, reduce BTA speeds by 10–15% and feeds by 15–20%.
Stainless steel requires aggressive chip breaking. Look for inserts or nose grinds with:
Positive rake angle (10–15°) to reduce cutting forces and work hardening
Chip breaker geometry designed for stringy materials
Sharp cutting edge (no chamfer) for austenitic grades
Coolant Strategy
Parameter
Recommended
Why
Coolant type
Neat oil (EP fortified) or high-EP emulsion (10–12%)
Extreme pressure additives reduce BUE
Coolant pressure
20–30% above standard for the diameter
Ensures adequate cooling at the cutting edge
Filtration
10–20 micron minimum
Prevents abrasive particles from accelerating wear
Temperature
30–35°C (lower end of range)
Reduces chemical reactivity at the cutting interface
Common Problems
Problem
Cause
Solution
Built-up edge
Workpiece material welding to carbide
Increase speed 10%; switch to AlTiN coating
Rapid tool wear
Abrasive wear from work-hardened layer
Use fine-grain carbide; increase coolant pressure
Chip packing
Stringy chips from low feed
Increase feed 10–15%
Poor surface finish
BUE breaking off and scratching bore
Increase speed; check coolant EP additives
Chatter
Work hardening causing uneven cutting forces
Reduce speed; increase feed slightly
Oversize hole
BUE on cutting edge increases effective diameter
Check edge condition; increase speed
Summary
Stainless steel deep hole drilling requires aggressive chip breaking, adequate coolant pressure (20–30% above standard), and AlTiN-coated fine-grain carbide tools. Austenitic grades (304/316) are the most challenging due to work hardening and stringy chips. Free-machining grades (416) drill much more easily. Increase feed rate to promote chip breaking, and never let the tool dwell in the cut — work hardening occurs almost instantly when the tool stops moving.