Deep Hole Drilling Method Comparison

This page provides a side-by-side comparison of all major deep hole drilling methods across the parameters that matter most for method selection: diameter range, depth capability, precision, surface finish, penetration rate, machine requirements, and relative cost.

Use this comparison table as a quick reference when evaluating which method to use for a specific application.

Comparison Table

ParameterGun DrillingBTA DrillingEjector DrillingTrepanningEDMLaser
Diameter range0.5–50 mm18–500 mm18–200 mm50–1,000+ mm0.1–6 mm0.01–1 mm
Optimal diameter1–25 mm25–150 mm20–65 mm100–500 mm0.5–3 mm0.05–0.5 mm
Max depth ratio300:1100:1100:140:140:120:1
Diameter tolerance±0.025 mm±0.05 mm±0.04 mm±0.10 mm±0.005 mm±0.01 mm
Surface finish Ra0.4–0.8 µm0.8–3.2 µm0.8–3.2 µm1.6–6.3 µm0.2–1.6 µm0.4–3.2 µm
Straightness per 300 mm0.08 mm0.10 mm0.10 mm0.15 mm0.05 mm0.10 mm
Relative feed rate1× (baseline)5–7×4–6×2–3×0.01×10–100× (per hole)
Material removalMechanicalMechanicalMechanicalMechanicalThermal erosionThermal
Material applicabilityAll machinableAll machinableAll machinableAll machinableConductive onlyMost materials
Machine typeDedicated or retrofitDedicated BTACNC lathe/MC retrofitDedicated BTA/trepanEDM machineLaser system
Workpiece seal?Bushing onlyPressure headNonePressure headNoneNone
Coolant pressureUp to 140 bar20–60 bar20–40 bar20–40 barNone (dielectric)None
Tooling costLow-moderateModerateModerate-highHighHighVery high
Machine investment$50K–$500K$200K–$3M$20K–$100K (retrofit)$300K–$1M$100K–$500K$200K–$1M
Per-hole cost (same dia)ModerateLow (high volume)Low-moderateModerate (material savings)HighVery high

These are advertised maxima. See deep hole drilling depth limits for practical production ratios and what actually caps each method. | Secondary ops needed? | Rarely | Sometimes | Sometimes | Usually (finish bore) | Rarely | Sometimes |

Method Characteristics

Gun Drilling

  • Strengths: Highest precision, best surface finish, extreme depth ratios, widest diameter range
  • Weaknesses: Slowest penetration rate, limited to 50 mm max diameter, external chip evacuation can scratch bore
  • Best for: Small precision holes, fuel injectors, medical implants, firearm barrels, mold cooling channels

BTA Drilling

  • Strengths: Fastest penetration rate, largest diameter range, clean internal chip evacuation, rigid tool system
  • Weaknesses: Requires dedicated machine, needs pressure head seal, cannot drill below 18 mm
  • Best for: High-volume production, oil and gas components, automotive crankshafts, landing gear

Ejector Drilling (DTS)

  • Strengths: No workpiece seal required, retrofittable to standard CNC machines, lower coolant pressure
  • Weaknesses: Slightly slower than BTA, larger minimum diameter (18 mm), less rigid than single tube
  • Best for: CNC lathe retrofits, irregular entry surfaces, job shops with moderate volume

Trepanning

  • Strengths: Material savings (~82% utilization on core), lower power requirements, good for very large diameters
  • Weaknesses: Lower precision, usually requires secondary finishing, limited depth ratio
  • Best for: Expensive materials (titanium, Inconel), thick-walled tubing, applications where core has value

EDM

  • Strengths: No cutting forces, can machine hardened materials, excellent precision for small holes
  • Weaknesses: Very slow, limited to conductive materials, electrode wear limits depth
  • Best for: Cooling holes in turbine blades, hardened tool steel, small precise holes in difficult materials

Laser Drilling

  • Strengths: Extremely fast for small holes, no tool wear, can drill at angles, non-conductive materials
  • Weaknesses: Limited depth, heat-affected zone, high equipment cost, recast layer
  • Best for: Thin materials, angled holes, high hole counts, non-conductive materials (ceramics)

Specification Comparison by Application

For Small Precision Holes (Ø 1–12 mm)

RequirementRecommended MethodWhy
Highest precisionGun drilling±0.025 mm tolerance, Ra 0.4 µm finish
Extreme depth (> 100:1)Gun drillingOnly method that achieves 300:1
Hardened materialEDMNo mechanical force; machines any conductive material
Very small hole (< 1 mm)EDM or laserGun drills not available below 0.5 mm
High volumeMulti-spindle gun drillingMultiple spindles compensate for slow penetration

For Medium-Diameter Holes (Ø 20–65 mm)

RequirementRecommended MethodWhy
Highest productivityBTA drilling5–7× faster than gun drilling
CNC lathe availableEjector drillingLower capital investment, no dedicated machine
Irregular entry faceEjector drillingNo pressure head seal needed
Best surface finishGun drillingRa 0.4–0.8 µm
Budget-sensitiveGun drilling on CNC retrofitLowest tooling cost

For Large Holes (Ø > 65 mm)

RequirementRecommended Method
Standard productionBTA drilling
Expensive materialTrepanning (core salvage)
Limited machine powerTrepanning (lower cutting forces)

Machine Investment vs. Production Volume

$1M+     │
         │         BTA (dedicated)
$500K    │
         │    BTA          Trepan
$200K    │   Gun drill
         │  Gun drill
$100K    │
         │ Ejector (CNC retrofit)
$50K     │
         │
         └─────────────────────────
            100   1K   10K   100K
                 Holes per year

Summary

The table above provides a comprehensive comparison of all major deep hole drilling methods. For most applications, the choice narrows quickly: gun drilling for small holes and precision, BTA for high-volume production and large diameters, ejector for CNC lathe retrofits, trepanning for material savings at large diameters, and EDM/laser for holes that mechanical methods cannot produce. Use this comparison table together with the decision framework to select the optimal method for your application.

For detailed guides on each method, see deep hole drilling methods overview. For a complete overview, visit the drilling methods guide.