30-Second Summary: The following are the most commonly used technical terms in deep hole drilling. Mastering these terms will help you read technical documentation, communicate with suppliers, and understand machining standards.
| Term | Description |
|---|---|
| Gundrill / Single-Lip Drill | Single cutting edge, V-groove external chip removal deep hole drill. The most common tool for holes 1-50 mm diameter with L/D up to 400:1. |
| BTA (Boring and Trepanning Association) | Single tube internal chip removal deep hole drilling method. Uses external coolant supply around the drill tube; chips exit through the tube interior. Typically 5-7× faster feed rates than gun drilling. |
| STS (Single Tube System) | Same as BTA — single drill tube serves as chip evacuation channel. Coolant is supplied externally between the bore wall and the tube. |
| DTS (Double Tube System) | Ejector drilling method using two concentric tubes with Venturi effect suction for chip evacuation. Requires lower coolant pressure than BTA but more complex tooling. |
| Ejector Drilling | Method using Venturi effect suction for chip evacuation through an inner tube. Can operate at lower coolant pressures (5-20 bar) than BTA. |
| Trepanning | Annular cutting that preserves the center core material. Used when the core has value or when full-section drilling would require excessive power. |
| Skiving & Roller Burnishing | Combined cutting (skiving) and cold press finishing (roller burnishing) completed in one pass. Produces mirror-like surface finish (Ra < 0.2 μm) in thin-wall tubing. |
| Pull Boring | Finishing method where the tool is pulled through an existing pre-drilled or cast hole. Often used as a final sizing operation to improve straightness and surface finish. |
| Guide Pad / Support Pad | Carbide or PCBN strips mounted on the tool body that provide guidance and burnish the bore surface during drilling. Critical for hole straightness and surface quality. |
| Pressure Head / BOZA | Device in BTA system that injects coolant into the annular space between the bore wall and drill tube, and provides sealing at the workpiece entry. |
| Rotary Union | Device that transfers coolant from stationary piping to a rotating tool or spindle. Must handle high pressure (up to 170 bar) and high RPM without leakage. |
| Whip Guide | Support device that prevents slender drill tube from whipping or oscillating during deep hole drilling. Placed along the tube path between the machine headstock and workpiece. |
| Depth-to-Diameter Ratio (L/D) | Ratio of hole depth to diameter. >10:1 is considered deep hole drilling. >100:1 is considered very deep. Gun drilling can achieve up to 400:1 in favorable materials. |
| Self-Piloting | Property of deep hole drilling tools that allows them to guide themselves via guide pads against the bore wall, requiring no external guidance or bushing once engaged. |
| Chip Breaker | Groove or step on the tool rake face that curls and breaks chips into short, manageable segments. Essential for materials that produce continuous chips (low-carbon steel, aluminum, copper). |
| Counter-Rotation | Tool and workpiece rotate in opposite directions. Reduces the relative surface speed on the guide pads and improves hole straightness by canceling out radial force components. Common for hard materials and deep holes. |
| Peck Cycle | Drilling cycle with periodic retraction to break and evacuate chips. In deep hole drilling, full retraction cycles (G83) are preferred over partial retraction (G73) for reliable chip clearance. |
| Regrinding | Re-sharpening of used drills by grinding the cutting face. Brazed carbide gundrills can typically be reground 5-15 times before the carbide or tube is consumed. See Tool Regrinding guide. |
| VDI 3208 / 3209 / 3210 / 3211 | German Engineers Association (VDI) series of deep hole drilling standards covering gun drilling, BTA systems, overview, and machining center operations respectively. |