Deep Hole Drilling Equipment: A Complete Overview
Choosing the right deep hole drilling machine is a capital decision that affects your capability, cycle times, and cost per hole for years. This guide covers the equipment types available, specifications from leading manufacturers, and guidance on matching machine features to your applications.
Machine Types and Configurations
Gun Drilling Machines
Gun drilling machines use a single-lip tool with internal coolant delivery and external chip evacuation through a V-shaped flute. They are the standard for hole diameters from 1 mm to 50 mm at depth-to-diameter ratios up to 100:1 or more.
Common configurations:
- Horizontal — Most common; ideal for long, slender workpieces (shafts, barrels, tubes)
- Vertical — For heavy workpieces that are easier to load vertically; gravity aids chip evacuation
- Single-spindle — Maximum flexibility for job shop work
- Multi-spindle (2 — 8) — High-volume production; multiple holes drilled simultaneously
Key features to evaluate:
- Spindle speed range (typically 1,500 — 24,000 rpm; small diameters require high speed)
- Coolant pressure (60 — 207 bar / 3,000 PSI for micro drilling)
- Counter-rotation capability (workpiece rotates opposite to tool for improved concentricity)
- Whip guide system (supports long drills to prevent deflection)
- Automation readiness (robotic loading, tool monitoring, lights-out operation)
BTA Drilling Machines
BTA (Boring and Trepanning Association) machines use a multi-edge tool with external coolant delivery and internal chip evacuation. They cover diameters from 12 mm to 500+ mm at 5 — 7 times the feed rate of gun drilling for equivalent diameters.
Configurations:
- Rotating workpiece (for shafts and cylindrical parts)
- Rotating tool (for non-cylindrical parts and molds)
- Combination gun drill + BTA (switchable on the same machine)
Combination Machines (Gun Drill + BTA)
Several manufacturers offer machines that can run both gun drilling and BTA processes on a single platform. Mollart’s MD-BTA series can change over between methods in under 10 minutes with dedicated pumps for each process (Mollart, 2024). Precihole’s column-type machines and UNISIG’s UNI series also offer dual-process capability.
Skiving & Roller Burnishing Machines
Skiving and roller burnishing (SRB) is a finishing process for hydraulic cylinder tubes. Skiving uses carbide blades to create a geometrically round bore, then roller burnishing cold-works the surface to a mirror finish.
| Parameter | Typical Value |
|---|---|
| Bore diameter | 30 — 600 mm |
| Length | Up to 16 m |
| Tolerance | IT7 — IT9 |
| Surface finish Ra | 0.05 — 0.4 µm |
| Roundness | 0.036 mm / 200 mm diameter |
| Skiving depth of cut | 0.5 — 10 mm per side |
SRB has largely replaced honing for hydraulic cylinder production because it is faster, produces better surface quality (Ra 0.05 — 0.2 µm), and eliminates the “stick-slip” problem common in honed tubes (UNISIG; ECOROLL; SRB Technology, 2024).
CNC Conversion
Converting an existing CNC machining center for deep hole drilling is the most cost-effective entry point for lower production volumes and L/D ratios below 40:1.
Required components:
| Component | Typical Specification | Cost Range |
|---|---|---|
| High-pressure coolant system | 70 — 140 bar, through-spindle | $15,000 — $40,000 |
| Coolant filtration | 10 — 15 µm paper band filter | $5,000 — $15,000 |
| Whip guide / bushing holder | Supports drill at entry | $2,000 — $8,000 |
| Tooling package | Gun drills, holders, bushings | $3,000 — $10,000 |
| Total retrofit | $27,000 — $78,000 |
Limitations: Practical L/D limit ~40:1, no counter-rotation, limited to gun drilling and shallow BTA.
See our selection checklist for a detailed cost comparison of new vs used vs conversion.
Manufacturer Comparison
UNISIG (USA)
UNISIG offers the broadest machine range, from micro gun drilling to heavy BTA and skiving/burnishing.
| Series | Process | Diameter | Depth | Key Feature |
|---|---|---|---|---|
| UNE6 | Gun drilling | 0.8 — 6 mm | 750 mm | Medical precision, 28,000 rpm, 3,000 PSI coolant |
| UNE | Gun drilling | 1.4 — 40 mm | 3,000 mm | Job shop / production, robot-ready |
| B-Series | BTA | 20 — 500 mm | 12 m | High-power landing gear drilling |
| S-Series | Skiving/Burnish | up to 305 mm | 10 m | Hydraulic cylinder finishing |
| UNI Series | Gun + BTA | 20 — 250 mm | 12 m | Modular production machine |
Notable case studies: Alta Precision landing gear (B700, 9“ bore × 7 ft deep in 300M steel); MSI Mold Builders (USC-3M hybrid, +5% mold output); surgical manufacturer (UNE6, 50% cycle time reduction) (UNISIG, 2024).
TBT (Germany)
TBT (Tiefbohrtechnik) is the global market leader in deep hole drilling technology.
| Series | Process | Diameter | Depth | Spindles |
|---|---|---|---|---|
| ML200 — ML700 | Gun + BTA | 0.8 — 400 mm | 700 — 15,000 mm | 1 — 6 |
| B Series | High-speed gun | Up to 40 mm | Up to 4,500 mm | 1 — 6 |
| BW Series | Heavy BTA | Up to 500 mm | Up to 12,000 mm | 1 — 4 |
| T Series | Precision gun | 2 — 10 mm | 400 mm | 3 |
ML series machines feature Siemens CNC, positioning accuracy ±0.02 mm, and capability for both ELB (gun) and BTA drilling (TBT, 2024).
Mollart (UK)
Mollart’s MD series offers high-flexibility combined gun/BTA machines.
| Series | Process | Diameter | Depth | Spindles |
|---|---|---|---|---|
| MD1 — MD8 | Gun + BTA | 5 — 50 mm solid | Up to 4,000 mm | 1 — 8 |
| Drillsprint | Gun | Up to 25 mm | 2,000 mm | 1 — 4 |
| Micro Drill | Gun | Up to 6 mm | 300 mm | 1 — 4 |
| Prismabore | 5-axis combo | Up to 40 mm | 2,000 mm | Gun + mill |
| Centeplex | 6-axis combo | Up to 90 mm | 4,500 mm | Gun + mill |
Mollart’s MD1-BTA can switch between gun drilling and BTA in under 10 minutes. Achieved tolerances include runout of 0.030 mm TIR over 500 mm and surface finish 0.4 Ra in 15-5 PH steel (Mollart, 2024).
Precihole (India)
Precihole offers cost-competitive machines for mid-range applications.
| Series | Process | Diameter | Depth | Power |
|---|---|---|---|---|
| BVN40 — BVN250 | BTA | 19 — 250 mm | Up to 12,000 mm | 15 — 115 kW |
| PMTC | Gun + BTA | 5 — 25 mm | 1,000 mm | 10 + 10 HP |
| XYGVNCL | Column-type | Various | Up to 3,000 mm | Multi-axis |
Precihole machines use Fanuc or Siemens controls with customized monitoring screens, high-pressure coolant with 25 µm filtration, and optional counter-rotation (Precihole, 2024).
Chinese Manufacturers
Chinese manufacturers (EsTop, Gooda, Dezhou Jutai, Zonjet, Guanlu) offer cost-effective solutions that have improved significantly in quality:
| Model | Process | Diameter | Depth | Price Range |
|---|---|---|---|---|
| DD40E/2 (FINCM) | Gun/BTA | 14 — 40 mm | 800 mm | $50,000 — $80,000 |
| ZJG08 (Zonjet) | Gun/BTA | 10 — 40 mm | 800 mm | $40,000 — $70,000 |
| TGK20D (Guanlu) | SRB | 40 — 200 mm | 4,000 mm | On request |
Machine Selection by Application
| Application | Recommended Machine Type | Key Specification |
|---|---|---|
| Medical bone screws (Ø1 — 3 mm) | UNISIG UNE6 or micro gun drill | 24,000+ rpm, 3,000 PSI coolant, counter-rotation |
| Automotive crank shaft oil holes | Multi-spindle gun drill (4 — 6 spindles) | 60 — 80 bar coolant, auto load/unload |
| Injection mold cooling channels | 3+2 axis hybrid drill/mill | 100+ bar coolant, 5-axis positioning |
| Landing gear (200+ mm bore) | BTA machine (UNISIG B or TBT BW) | 100+ HP, counter-rotation, 12 m capacity |
| Hydraulic cylinder tubes | Skiving & roller burnishing machine | 0.05 — 0.4 µm Ra, 16 m length |
| General job shop (variety) | Single-spindle gun drill or CNC conversion | Wide diameter range, quick changeover |
| High-volume production | Multi-spindle dedicated line | Cycle time < 30 sec per part |
Machine Specification Checklist
When evaluating any deep hole drilling machine, verify:
- Diameter range required (current and future parts)
- Maximum depth / bed length
- Spindle speed range (adequate for smallest diameter)
- Spindle power (adequate for largest diameter in toughest material)
- Coolant pressure and flow rate (at the tool tip, not at the pump)
- Coolant filtration specification (10 — 25 µm typical)
- Counter-rotation available (recommended for L/D > 20:1)
- Whip guide type and adjustability
- CNC control and monitoring features
- Automation interface (robot, gantry, or conveyor)
- Floor space, foundation requirements, and power supply
- Tooling availability and regrind service
- Manufacturer service and technical support in your region
References
- UNISIG. Machine Series Overview — UNE6, UNE, B-Series, S-Series, UNI Series. 2024.
- UNISIG / CTE Magazine. Moldmaking Multitasking — USC-3M Case Study. 2024.
- UNISIG / Aero-Mag. Handling the Challenges of Landing Gear Drilling. 2024.
- UNISIG. Combining Skiving and Burnishing for Cylinder Bores. Technical Article, 2024.
- TBT Tiefbohrtechnik. ML Series — Multifunctional Deep Hole Drilling Machines. Product Literature, 2024.
- TBT Tiefbohrtechnik. Machine Models — B, BW, T Series. Technical Specifications, 2024.
- Mollart. MD1-BTA Combined Gun Drilling and BTA Machine. Technical Data, 2024.
- Mollart. Machinery — Micro Drill, Drillsprint, Prismabore, Centeplex. Product Overview, 2024.
- Precihole Machine Tools. BVN Series BTA Deep Hole Drilling Machines. Specifications, 2024.
- Precihole Machine Tools. PMTC Series Column-Type Multi-Axis Machines. Specifications, 2024.
- ECOROLL AG. Combined Skiving/Roller Burnishing — Fast Internal Machining of Cylinder Tubes. Technical Brochure, 2024.
- SRB Technology. Skiving Roller Burnishing — Process Overview and Specifications. 2024.
- Guanlu. TGK20D Deep Hole Skiving Roller Burnishing Machine. Specifications, 2024.
- Artizono. Comprehensive Guide to CNC Deep Hole Drilling Machines for Industrial Applications. 2024.
- FINCM / Made-in-China. DD40E/2 Multi Spindle Deep Hole CNC Gun Drilling Machine. 2024.
- Zonjet. ZJG08 CNC Deep Hole Drilling Machine. Technical Specifications, 2024.
- Bourn-Koch / Mollart. What is Deep Hole Drilling? — Equipment Overview. 2024.
- CNC Bulletin. What is Deep Hole Drilling Machine? — Types and Configurations. 2024.