Deep Hole Drilling in the Automotive Industry
The automotive industry is one of the largest users of deep hole drilling technology. Modern engines, transmissions, fuel systems, and — increasingly — electric vehicle components depend on deep, precise holes that conventional drilling cannot produce.
This guide covers the main automotive applications, the parameters used in production, and how the shift to EVs is changing deep hole drilling requirements.
Key Applications and Parameters
1. Crankshaft Oil Holes
Crankshafts require deep, straight oil passages to supply lubricant to main bearings and connecting rod journals. These holes are typically drilled from the main bearing journal surface to the crankpin at an angle, creating depth-to-diameter ratios of 20:1 to 50:1.
Typical specifications:
| Parameter | Value |
|---|---|
| Diameter | 4 — 12 mm |
| Depth | 80 — 300 mm |
| L/D ratio | 20:1 — 50:1 |
| Tolerance | IT8 — IT9 (H8/H9) |
| Surface finish | Ra 1.6 — 3.2 µm |
| Straightness | ≤ 0.1 mm per 100 mm |
| Material | Forged steel or ductile cast iron |
Production parameters (gun drilling):
- Cutting speed: 60 — 120 m/min (carbon steel), 50 — 100 m/min (alloy steel)
- Feed: 0.12 — 0.30 mm/rev (5 — 10 mm diameter)
- Coolant: 80 bar, oil-based, through-tool
- Tool: Solid carbide gun drill, TiAlN-coated, 12×D to 30×D lengths
Sandvik’s CoroDrill 861 is designed for depths of 12×D to 30×D in diameters from 3 to 20 mm, achieving H8/H9 tolerances (Sandvik Coromant, 2024). ISCAR offers solid carbide 20×D drills specifically for crankshaft oil hole applications (ISCAR Hole Making Catalog, 2024).
Production approach: High-volume crankshaft lines use multi-spindle gun drilling machines, with two to six spindles drilling multiple oil holes simultaneously. Cycle times are typically 30 — 90 seconds per hole depending on depth and diameter.
2. Connecting Rods
Connecting rods require oil passages for wrist pin lubrication, typically small-diameter holes drilled at angles through hardened steel.
| Parameter | Value |
|---|---|
| Diameter | 3 — 8 mm |
| Depth | 60 — 150 mm |
| L/D ratio | 15:1 — 30:1 |
| Tolerance | IT8 — IT9 |
| Surface finish | Ra 1.6 — 3.2 µm |
A production case study on SAE 4140 connecting rods (0.250“ diameter, 9“ depth) using a six-spindle gun drilling machine achieved 70 parts per hour with zero scrap (CTE Magazine, 2024).
3. Engine Block Oil Galleries
Engine blocks contain extensive oil gallery networks that supply lubricant to crankshaft bearings, camshaft bearings, and valvetrain components. These are produced by drilling intersecting straight holes from multiple directions.
Guhring documents a production application drilling main oil galleries in aluminum cylinder heads:
| Parameter | Value |
|---|---|
| Tool | RT 100 T ALU, 6.95 mm |
| Depth | 2 × 210 mm (drilled from both sides) |
| Cutting speed | 110 m/min |
| Feed rate | 1500 mm/min |
| Coolant | 50 bar, soluble oil |
| Tool life | 500 meters of drilling |
See our aluminum deep hole drilling guide for a detailed breakdown of this application.
4. Fuel Injection Components
Diesel and gasoline direct injection systems require extremely precise holes in injector nozzles and valve bodies.
| Parameter | Diesel Injector Nozzles | GDI Injectors |
|---|---|---|
| Hole diameter | 100 — 300 µm | 150 — 250 µm |
| Depth | 0.7 — 1.1 mm | 0.5 — 1.0 mm |
| L/D ratio | 10:1 — 12:1 | 8:1 — 10:1 |
| Diameter tolerance | ±2 µm | ±1.5% area |
| Surface finish (as-drilled) | Ra 0.4 — 1.25 µm | Ra < 0.2 µm (after processing) |
| Surface finish (post-process) | Ra 0.1 — 0.4 µm | Ra < 0.2 µm |
Manufacturing methods:
- Micro-EDM: Achieves ±2 µm dimensional accuracy with taper angles of 0 — 1.3° (ScienceDirect, 2012)
- Laser drilling: Percussion drilling (< 3 seconds) or trepanning (< 10 seconds), but requires subsequent hydroerosive grinding to meet final specifications
- Gun drilling: Used for larger fuel system components (pump bodies, valve housings), achieving IT6 — IT8 accuracy with drill deflection of 0.01 — 0.03 mm per 100 mm
Post-processing via hydroerosive grinding improves surface finish from Ra 0.4 µm to Ra 0.1 µm and calibrates flow rate (Mendeley, 2009).
5. Transmission Valve Bodies
Automatic transmission valve bodies contain complex networks of hydraulic control passages. These require precise hole positioning, burr-free intersections, and consistent diameters for valve spool operation.
| Parameter | Value |
|---|---|
| Diameter | 2 — 15 mm |
| Depth | 20 — 200 mm |
| L/D ratio | 10:1 — 40:1 |
| Tolerance | IT7 — IT8 |
| Surface finish | Ra 0.8 — 1.6 µm |
| Hole position accuracy | ±0.05 mm |
Gun drilling is preferred for transmission valve body passages because it produces a clean, burr-free hole in a single pass — critical for preventing valve sticking (TAES, 2024; Artizono, 2024).
6. Turbocharger Components
Turbocharger shafts and bearing housings require oil feed and return passages:
| Parameter | Value |
|---|---|
| Diameter | 2 — 8 mm |
| Depth | 30 — 100 mm |
| Tolerance | IT7 — IT9 |
| Straightness | 0.001“ per foot |
| Materials | Inconel, stainless steel, alloy steel |
A case study on a turbocharger bearing housing (SAE 4140, 45 HRC, 8 mm diameter, 60 mm depth) using a solid carbide drill with polished flutes and variable helix at 1,000 PSI coolant pressure reduced cycle time from 4.5 to 3.7 minutes per part (—18%), doubled tool life, and cut scrap from 15% to 3% (CTE Magazine / Hone-All Precision, 2024).
High-Volume Production Strategies
Automotive deep hole drilling differs from job-shop work in three ways: volume, automation, and cost per hole.
Multi-Spindle Machines
Multi-spindle deep hole drilling machines are the standard for high-volume automotive production. A six-spindle machine drilling connecting rods can achieve 70 parts per hour, compared to approximately 12 parts per hour on a single-spindle machine (CTE Magazine, 2024).
Typical automotive multi-spindle configurations:
- 2 spindles: Medium volume, flexible changeover
- 4 spindles: High volume, dedicated parts
- 6 — 8 spindles: Ultra-high volume, single part family
Automation Integration
UNISIG case studies document automotive cells where a multiple-spindle machine integrated with pick-and-place automation, conveyor loading, and automatic clamping produced over 100 parts per hour (UNISIG/CTE, 2024).
Tool Life Management
In high-volume production, tool life directly affects uptime. Typical targets:
- Carbide gun drills in steel: 30 — 90 meters of drilling per regrind
- PCD tools in aluminum: 500+ meters
- Indexable BTA inserts in cast iron: 200 — 500 edges
EV Transition: How Deep Hole Drilling Is Changing
The shift to electric vehicles is not eliminating deep hole drilling — it is redirecting it.
Components That Remain
| Component | Deep Hole Drilling Requirement |
|---|---|
| Transmission shafts (single-speed gearboxes) | Oil passages, spline lubrication holes |
| Thermal management systems | Cooling channels in battery plates and heat exchangers |
| E-motor housings | Coolant passages, sensor holes, dowel pin holes |
| Battery enclosures | Structural mounting holes, vent passages |
New Challenges in Aluminum
EV battery enclosures use large aluminum structural castings and extrusions, which present specific deep hole drilling challenges:
- Long, continuous chips — low-silicon aluminum produces stringy chips that are difficult to evacuate from deep holes
- Built-up edge — aluminum adhesion on cutting edges degrades surface finish
- Burr formation — excessive exit burrs require secondary deburring operations
- Thermal management — deep holes in aluminum generate significant heat; tool deflection and thermal drift are the greatest sources of dimensional error
Solutions:
- PCD-tipped gun drills for production runs (8 — 12× tool life over carbide)
- High-pressure through-tool coolant (70+ bar) for chip evacuation
- Circular milling as an alternative to drilling for long-chipping alloys (Seco Tools, 2024)
- DLC-coated tools to prevent built-up edge (PES Media, 2024)
Process Parameter Summary Table
| Component | Method | Diameter (mm) | Depth (mm) | Speed (m/min) | Feed (mm/rev) | Coolant (bar) |
|---|---|---|---|---|---|---|
| Crankshaft oil holes | Gun drill | 4 — 12 | 80 — 300 | 60 — 120 | 0.12 — 0.30 | 80 |
| Connecting rods | Gun drill | 3 — 8 | 60 — 150 | 60 — 100 | 0.08 — 0.20 | 60 — 80 |
| Engine block galleries | Gun drill | 6 — 12 | 200 — 500 | 80 — 130 | 0.10 — 0.30 | 40 — 70 |
| Fuel injector bodies | Gun drill | 1 — 6 | 10 — 60 | 30 — 60 | 0.005 — 0.025 | 80 — 120 |
| Transmission valve bodies | Gun drill | 2 — 15 | 20 — 200 | 80 — 180 | 0.02 — 0.10 | 50 — 80 |
| Turbocharger shafts | Gun drill | 2 — 8 | 30 — 100 | 30 — 60 | 0.01 — 0.04 | 70 — 100 |
| Battery enclosure cooling | Gun drill | 4 — 12 | 50 — 300 | 150 — 250 | 0.02 — 0.08 | 60 — 80 |
References
- Sandvik Coromant. CoroDrill 861 — Deep Hole Drills for Automotive Applications. Technical Data, 2024.
- ISCAR. Hole Making Catalog — Solid Carbide Deep Hole Drills for Crankshafts. Technical Catalog, 2024.
- Guhring. RT 100 T ALU Engine Block Oil Gallery Application. Technical Documentation, 2024.
- CTE Magazine. Going Deep and Cellular — Multi-Spindle Automotive Production. Cutting Tool Engineering, 2024.
- UNISIG. Case Studies — Automated Deep Hole Drilling Work Cells. 2024.
- TAES. Automotive Deep Hole Drilling — Valve Bodies and Transmission Components. Technical Brochure, 2024.
- Artizono. The Ultimate Guide to CNC Deep Hole Drilling Machines for Automotive Parts. 2024.
- Hone-All Precision. 4 Advantages of CNC Deep Hole Gundrilling for Enhancing Production Quality. Technical Blog, 2024.
- Seco Tools. From ICE to EV — Why Drilling Remains at the Core of Automotive Production. Technical Article, 2024.
- PES Media. The Path to Better Hole Making in Aluminium. 2024.
- ScienceDirect. Mechanism Design and Process Control of Micro EDM for Drilling Spray Holes of Diesel Injector Nozzles. 2012.
- Mendeley / ScienceDirect. Form Measurement Inside Fuel Injector Nozzle Spray Holes. 2009.
- SME. Deep Hole Drilling Aids Change in Auto Manufacturing. Society of Manufacturing Engineers, 2019.
- DG Flex Precision. Beyond the Blueprint — Custom Drilling for Automotive Performance Parts. 2024.
- Fabricating & Metalworking. Deep Hole Drilling of Diesel Engine Components and Transmission Shafts. 2024.