Ejector Drilling Applications
Ejector drilling (DTS) occupies a specific niche in the deep hole drilling landscape. It is not the fastest method (BTA holds that title) and it cannot reach the smallest diameters or highest precision (gun drilling wins there). But for shops that want to add deep hole drilling capability to existing CNC lathes — particularly for medium-diameter holes at low to moderate volumes — ejector drilling is often the most practical and economical choice.
This guide covers the applications where ejector drilling excels, the industries that benefit most, and case examples showing when to choose DTS over alternative methods.
When to Choose Ejector Drilling
Best-Fit Scenario
Ejector drilling is the right choice when three conditions are met:
- Hole diameter is 20–65 mm (the DTS sweet spot)
- Existing equipment is a standard CNC lathe or machining center
- Production volume does not justify a dedicated BTA machine
If all three conditions apply, ejector drilling is almost certainly the most cost-effective deep hole drilling method.
Secondary Indicators
These conditions further favor ejector drilling:
- Irregular workpiece entry face — Castings, forgings, or parts with rough surfaces where BTA’s pressure head seal would leak
- Frequent changeovers — Ejector drilling’s faster setup (no seal alignment) makes it ideal for job shops
- Limited capital budget — A DTS retrofit costs $30K–$100K versus $200K+ for a BTA machine
- Multiple hole sizes — Changing DTS heads is faster than retooling a BTA pressure head system
Industries and Applications
General Job Shops
Job shops that machine a variety of parts benefit most from ejector drilling’s flexibility.
| Application | Typical DTS Range | Why Ejector Drilling |
|---|---|---|
| Hydraulic cylinder bores | 25–100 mm, 500–3,000 mm deep | Can use existing lathes; no dedicated machine needed |
| Valve bodies | 20–80 mm | Irregular casting surfaces — no seal required |
| Shaft bores | 20–65 mm | Quick changeover between different shaft sizes |
| Mold cooling channels | 20–40 mm | Existing CNC equipment; moderate depth |
Case example: A general machine shop with 10 CNC lathes wants to add deep hole drilling. They drill approximately 500 holes per year in various shaft and cylinder components, diameters 20–60 mm. A DTS retrofit on one lathe costs $50K. A BTA machine would cost $350K and sit idle 60% of the time. DTS is the clear choice.
Maintenance and Repair (MRO)
Deep hole drilling is often required for repairing or enlarging existing bores in large components.
| Application | Typical DTS Range | Why Ejector Drilling |
|---|---|---|
| Enlarging worn cylinder bores | 40–150 mm | Can be done on a boring mill or large lathe |
| Removing broken tools | 25–65 mm | DTS can drill around broken tool fragments |
| Repairing hydraulic components | 20–80 mm | Quick setup; no seal needed on worn faces |
Medium-Volume Production
For production volumes of 500–5,000 holes per year, ejector drilling offers a compelling balance of productivity and capital cost.
| Application | Typical DTS Range | Production Volume |
|---|---|---|
| Pump shafts | 20–50 mm | 1,000–3,000/year |
| Motor shafts | 20–40 mm | 2,000–5,000/year |
| Connecting rods | 20–35 mm | 1,000–5,000/year |
| Transmission shafts | 25–50 mm | 500–2,000/year |
Case example: A manufacturer produces 2,000 pump shafts per year, each requiring a Ø25 mm × 600 mm deep axial bore. Current method: gun drilling on a dedicated machine, 8 minutes per hole. By switching to DTS on a CNC lathe, cycle time drops to 4 minutes per hole while freeing the gun drilling machine for other work. Capital cost of DTS retrofit: $45K. Payback period: 14 months.
Custom and One-Off Work
For large, expensive one-off parts, the elimination of the pressure head seal is ejector drilling’s most valuable feature.
| Application | Why Ejector Drilling |
|---|---|
| Large forging with rough surface | No seal needed on irregular workpiece face |
| Hardened component (post-heat treat) | Can drill after heat treatment without seal concerns |
| Part with existing cross-holes | DTS handles interrupted cuts better than BTA |
| Thin-walled tube drilling | Lower coolant pressure reduces risk of tube collapse |
When NOT to Use Ejector Drilling
Ejector drilling is not the right choice for:
- Holes under 18 mm diameter — The double-tube design cannot physically fit
- Extreme depth ratios (> 100:1) — DTS is limited to 100:1; gun drilling reaches 300:1
- Highest production volumes (> 10,000 holes/year at same size) — BTA’s faster penetration justifies a dedicated machine
- Maximum precision applications — Gun drilling delivers better tolerances and surface finish
- Extremely limited budget — Gun drilling (CNC retrofit) requires less coolant system investment
Application Decision Matrix
| Factor | Choose Gun Drilling | Choose Ejector Drilling | Choose BTA Drilling |
|---|---|---|---|
| Diameter | < 18 mm | 18–65 mm | > 65 mm |
| Depth ratio | > 100:1 | < 100:1 | < 100:1 |
| Production volume | Low to medium | Low to medium | Medium to high |
| Available machine | CNC lathe or dedicated | CNC lathe or MC | Dedicated BTA machine |
| Workpiece entry face | Any | Irregular OK | Must be flat/square |
| Capital budget | $50K–$500K | $30K–$100K | $200K–$3M |
| Precision requirement | Highest | Moderate | Moderate |
| Setup frequency | Moderate | High (fast changeover) | Low (long runs) |
Summary
Ejector drilling (DTS) is the most practical deep hole drilling method for shops that want to add deep hole capability to existing CNC machine tools. It excels at medium diameters (20–65 mm), moderate depth ratios (up to 100:1), and low-to-medium production volumes. The elimination of the workpiece seal makes it ideal for irregular entry surfaces and quick-changeover job shop environments. While BTA drilling is faster and gun drilling is more precise, ejector drilling offers the best combination of productivity and capital efficiency for the widest range of general machining applications.
For process fundamentals, see what is ejector drilling. For CNC lathe setup, see ejector drilling CNC setup. For method comparison, see ejector vs BTA vs gun drilling. For a complete overview, visit the ejector drilling guide.