Gun Drilling Machines: Types and Selection Guide
Gun drilling can be performed on several types of machines, ranging from purpose-built dedicated systems to retrofitted standard CNC equipment. The choice depends on your production volume, hole geometry requirements, and budget.
This guide covers the three main machine categories—dedicated gun drilling machines, CNC lathe retrofits, and modular units—and provides selection criteria to help you choose the right configuration.
Dedicated Gun Drilling Machines
Dedicated gun drilling machines are purpose-built for deep hole drilling and offer the best performance, especially for extreme depth ratios and precision requirements.
Key Features
- Contra-rotation: Both the workpiece and drill rotate in opposite directions, canceling rotational drift forces and improving straightness significantly. Straightness deviations can be held to within 0.03 mm over 150 mm.
- Integrated high-pressure coolant system: 1,000–2,000+ PSI coolant pumps are built into the machine, with proper filtration (10–20 micron) and temperature control.
- Whip guide support: Multiple whip guides (tool supports) are positioned along the drill path to prevent deflection and vibration at extreme depths. Large machines may have six or more whip guides.
- Process monitoring: Real-time monitoring of coolant pressure, torque, thrust force, and spindle load with automatic shutoff on fault conditions.
| Machine Category | Depth Ratio Capability | Typical Diameter Range | Typical Applications |
|---|---|---|---|
| Compact dedicated (1–2 spindles) | Up to 100:1 | 1.5–25 mm | Job shops, precision components |
| Production dedicated (2–8 spindles) | Up to 100:1 | 3–50 mm | Automotive, high-volume production |
| Large-bore dedicated | Up to 50:1 | 10–65 mm | Oil and gas, heavy equipment |
| Custom/special | Up to 300:1 | 0.5–40 mm | Aerospace, defense, extreme depth |
Advantages
- Best hole straightness and precision
- Highest depth ratio capability
- Integrated coolant and filtration systems
- Multiple spindles for high-volume production
- Contra-rotation for superior straightness
Disadvantages
- Highest capital investment ($100,000–$500,000+ per machine)
- Dedicated floor space required
- Less flexible for other types of machining
- Longer lead time for machine purchase and installation
Leading Manufacturers
| Manufacturer | Headquarters | Specialty | Machine Series |
|---|---|---|---|
| UNISIG | Wisconsin, USA | Full range, aerospace focus | U5, U8, U9, custom |
| TBT (Tiefbohrtechnik) | Germany | Large machines, oil and gas | TBT 1-spindle, multi-spindle |
| Mollart Engineering | UK | Special purpose, defense | 7000, 8000 series |
| Botek | Germany | Small-to-medium diameters | BK, BKX, KX series |
| Somex | France | Multi-spindle production | Multi, Compact |
| Suhner | Switzerland | Modular drilling units | BEX, BEM series |
CNC Lathe Retrofit for Gun Drilling
Standard CNC lathes can be retrofitted for gun drilling by adding high-pressure coolant through the live tooling, a guide bushing, and whip guide supports. This is a cost-effective entry point for shops starting with gun drilling.
Key Requirements
- High-pressure coolant unit: Standalone coolant pump (500–1,500 PSI) with fine filtration, plumbed through the lathe’s live tooling system or a dedicated toolholder.
- Guide bushing mount: Bushing holder mounted on the turret, tailstock, or a dedicated bracket. Precise alignment with the spindle axis is critical.
- Pilot hole capability: The lathe must be able to drill a pilot hole on-center, either with a live tool or by using a center drill in the tailstock.
- Whip guide support: For depths exceeding 30–40× diameter, a whip guide must be positioned between the tailstock and workpiece.
Capability on a CNC Lathe
| Parameter | Typical Limit |
|---|---|
| Maximum depth ratio | 40:1 (without whip guide), 60:1 (with whip guide) |
| Diameter range | 3–25 mm |
| Typical tolerance | ±0.05 mm |
| Straightness | 0.12 mm per 300 mm |
| Surface finish | Ra 0.8–1.6 µm |
Advantages
- Much lower capital investment ($20,000–$60,000 for retrofit)
- Dual-purpose machine (standard turning + gun drilling)
- Familiar programming environment (standard G-code)
- Faster setup for job shop work
Disadvantages
- Limited depth ratio (no contra-rotation)
- No integrated process monitoring
- Coolant system may be less capable than dedicated machine
- Single-spindle only (low production volume per machine)
- Occupies a lathe that could otherwise do turning work
Modular Gun Drilling Units
Modular gun drilling units are self-contained drilling heads that can be mounted on existing machine tools—large boring mills, floor mills, or custom workholding fixtures.
How They Work
A modular unit includes a spindle motor, a high-pressure coolant swivel, and a feed mechanism in a compact package. The unit is bolted to the machine table or ram and uses the host machine’s positioning system for alignment.
| Feature | Typical Specification |
|---|---|
| Spindle power | 3–15 HP |
| Spindle speed | 500–10,000 RPM |
| Coolant pressure | 500–1,500 PSI (external pump required) |
| Depth ratio | Limited by host machine rigidity |
| Mounting | Bolt-on to machine table, ram, or column |
Advantages
- Can gun-drill very large parts that don’t fit in a dedicated machine
- Relatively low cost ($30,000–$80,000 for the drilling unit)
- Portable—can be moved between machines
- Good for large, one-off parts (molds, dies, heavy equipment)
Disadvantages
- Limited depth ratio (no whip guide integration)
- Dependent on host machine rigidity and alignment
- Manual or semi-automated process
- Not suitable for high-volume production
Machine Selection Criteria
By Production Volume
| Volume | Recommended Machine Type |
|---|---|
| Prototype / R&D (1–50 parts/year) | CNC lathe retrofit or contract service provider |
| Low production (50–500 parts/year) | CNC lathe retrofit or compact dedicated machine |
| Medium production (500–5,000 parts/year) | Dedicated single-spindle machine |
| High production (5,000+ parts/year) | Dedicated multi-spindle machine |
By Depth Ratio
| Depth Ratio | Machine Type |
|---|---|
| Up to 30:1 | CNC lathe retrofit (lowest cost) |
| 30:1 to 60:1 | Dedicated machine or retrofitted lathe with whip guide |
| 60:1 to 100:1 | Dedicated machine required |
| Over 100:1 | Specialized dedicated machine with contra-rotation |
By Diameter
| Diameter | Machine Considerations |
|---|---|
| Under 3 mm | High spindle speed required (>6,000 RPM). Solid carbide drills. High coolant pressure (1,500+ PSI). |
| 3–12 mm | Most common range. Well-served by both dedicated and retrofitted machines. |
| 12–25 mm | Moderate coolant pressure (300–500 PSI). Both dedicated and retrofit suitable. |
| Over 25 mm | Dedicated machine preferred. Higher horsepower required. |
By Tolerance Requirement
| Tolerance Grade | Recommended Machine |
|---|---|
| ±0.05 mm or looser | Any machine type suitable |
| ±0.025 mm | Dedicated machine with contra-rotation recommended |
| ±0.013 mm or tighter | Dedicated machine required; CNC retrofit unlikely to hold |
Make vs. Buy Decision
Before investing in a gun drilling machine, consider whether outsourcing makes more sense for your volume and requirements.
| Factor | Favor In-House Machine | Favor Outsourcing |
|---|---|---|
| Annual volume | >500 holes/year | <500 holes/year |
| Depth ratio | Consistent (same range) | Varies widely |
| Lead time | Need same-day turnaround | Can wait 1–2 weeks |
| Capital available | Budget approved | Limited capital |
| Core competency | Deep hole drilling is core to business | Occasional requirement |
| Special requirements | Proprietary/tolerances require control | Standard tolerances |
For help evaluating providers, see our guide to choosing a gun drilling service provider.
Summary
Dedicated gun drilling machines offer the best performance and highest depth ratios, while CNC lathe retrofits provide a low-cost entry point for job shops and low-volume production. Modular units handle very large parts that cannot be moved to a dedicated machine. The right choice depends on your production volume, depth ratio, diameter range, and tolerance requirements—as well as whether in-house drilling or a contract service provider makes better economic sense.
For a comparison of gun drilling with other deep hole drilling methods, see our gun drilling vs BTA vs ejector guide. For a complete overview, visit the gun drilling guide.