Deep Hole Drilling Method Selection Calculator Tool

Deep Hole Drilling Method Selection Calculator Tool

Selecting the right deep hole drilling method is the most consequential decision in any deep hole drilling project. The wrong choice leads to excessive tooling costs, poor surface finish, low productivity, or the inability to produce the hole at all.

This guide provides a structured decision framework — a selection calculator — that takes key input parameters and guides you to the optimal drilling method.

Input Parameters

The selection calculator requires six inputs:

Decision Logic — Step by Step

Step 1: Diameter Check

Diameter < 0.5 mm   →  EDM, laser, or micro-gun drilling
0.5 mm ≤ Ø < 18 mm  →  Gun drilling (primary), EDM/laser (if non-conventional required)
18 mm ≤ Ø < 50 mm   →  Gun drilling or BTA (both viable — proceed to Step 2)
50 mm ≤ Ø < 250 mm  →  BTA drilling (primary), ejector (retrofit), trepanning (for large solid bores)
Ø > 250 mm          →  Trepanning or BTA (special machines only)

Step 2: Depth Ratio Check

L/D < 10:1          →  Conventional drilling may be sufficient (consider gun drilling if tight tolerance)
10:1 ≤ L/D < 50:1   →  Gun drilling, BTA, or ejector — all viable depending on diameter
50:1 ≤ L/D < 100:1  →  Gun drilling (Ø < 50 mm), BTA (Ø > 18 mm with reduced parameters)
100:1 ≤ L/D < 200:1 →  Gun drilling only (limitations on diameter and feed rate)
L/D > 200:1         →  Gun drilling with advanced vibration suppression, reduced parameters

Depth-to-diameter ratio by method capability:

Step 3: Precision Check

IT6–IT8 (> 10 µm)   →  Gun drilling (primary), BTA marginal at upper end
IT8–IT10 (10–30 µm) →  Gun drilling, BTA, ejector (all capable)
IT10–IT12 (30–80 µm)→  Any deep hole method with proper setup
IT12+ (> 80 µm)     →  Conventional drilling may be adequate

Surface finish achievable by method (as-drilled, no secondary op):

Step 4: Production Volume Check

Prototype / low volume (1–100 parts/year):
    → Flexible approach: gun drilling on retrofitted CNC, or contract service provider
    → Considerations: tool cost per hole is secondary; setup time is primary

Medium volume (100–10,000 parts/year):
    → Dedicated gun drilling or BTA machine with optimized tooling
    → Multi-spindle machines become economical at > 1,000 parts/year

High volume (> 10,000 parts/year):
    → Dedicated multi-spindle gun drilling or BTA machines
    → Rotary transfer machines for automotive-scale production
    → Tool cost optimization is primary driver

Step 5: Material Consideration

Method Selection Matrix

The following matrix combines all six inputs into a recommendation:

Cost Comparison Quick Reference

Estimated relative cost per hole by method (gun drilling = baseline 1.0x):

Complete Selection Workflow

START: Hole required
  │
  ├── Ø < 0.5 mm ─────────────────────────→ EDM / laser / micro-gun
  │
  ├── 0.5 ≤ Ø < 18 mm ─── L/D > 100:1? ──→ Gun drilling
  │                              └─ no ──→ Gun drilling (standard)
  │
  ├── 18 ≤ Ø < 50 mm ──── L/D > 80:1? ───→ Gun drilling
  │                     └─ L/D ≤ 80:1 ───→ Check precision:
  │                                            IT6–IT8 → Gun drilling
  │                                            IT9+ → BTA or ejector
  │
  ├── 50 ≤ Ø < 250 mm ─── Retrofitting CNC? → Ejector drilling
  │                     └─ New machine? → BTA drilling
  │                     └─ Solid stock removal? → Trepanning
  │
  └── Ø ≥ 250 mm ──────── Material value high? → Trepanning
                                   └─ no → BTA (special machine)

Summary

The method selection calculator reduces a complex multi-variable decision to a structured step-by-step process. Diameter and depth ratio are the primary gates — they narrow the field to 1–2 viable methods. Precision, volume, and material then determine the optimal choice. For most applications below Ø50 mm, gun drilling is the default answer. Above Ø50 mm, BTA drilling offers the best productivity. Ejector drilling fills the retrofit gap, and trepanning is reserved for large, high-value blanks.

For detailed comparison of methods across all dimensions, see the methods comparison guide and the how to choose guide. For equipment selection based on method, refer to the equipment selection guide.