DEEP HOLE GUN DRILLING PREPRESS

Deep Hole Gun Drilling & BTA Toolpath Vector Prepress Guide

Deep hole drilling processes—including single-lip gun drilling, BTA (Boring and Trepanning Association), and ejector drilling—produce straight, high-tolerance holes with length-to-diameter ($L/D$) ratios from $20:1$ up to $250:1$.

1. Single-Lip Gun Drill vs BTA System Mechanics

Single-lip gun drills utilize internal pressurized coolant passages and external V-flute chip return, while BTA tools pump coolant externally around the drill tube and evacuate chips internally through the tool center. Carbide guide pads burnish hole walls to achieve $Ra \le 0.4–0.8\,\mu\text{m}$ surface finishes.

2. Engineering Specifications & Tolerances

3. Manifold Cross-Hole Intersect Vector DXF Prepress

• Step-Down Feed Zones: At cross-hole intersections, insert CAM feed deceleration zones starting $3.0\text{mm}$ before breakout and ending $3.0\text{mm}$ past breakthrough.
• Starter Pilot Bushing Concentricity: Pre-drilled pilot counterbore DXFs must specify $1.5\times D$ depth with $+0.005/-0.000\text{mm}$ diametral clearance and $140^\circ$ point angle match.
• Chip Flute Retract Clearances: Never program high-speed peck retract loops during deep hole drilling without shutting off spindle rotation to prevent catastrophic carbide pad chipping.