Ejector Drilling vs BTA for CNC Lathe Retrofit: Cost and Capability Comparison

Ejector Drilling vs BTA for CNC Lathe Retrofit

For shops adding deep hole drilling capability to an existing CNC lathe, ejector (DTS) and BTA (STS) are the two retrofit options. They use the same general principle — multi-edge cutting head with internal chip evacuation — but differ fundamentally in how coolant is delivered and chips are evacuated.

The choice between them for a retrofit application depends on cost, installation complexity, capability, and the specific parts being drilled.

System Comparison

Ejector (DTS) Retrofit

Component	Required	Approximate Cost
Coolant pump upgrade	Yes (15–40 bar, 80–350 L/min)	$5K–$15K
Coolant swivel	Yes (for rotating tool)	$2K–$5K
DTS boring bar	Yes (double-tube design)	$3K–$10K
DTS drill heads	Yes (various diameters)	$200–$800 each
Steady rest(s)	Recommended for > 30:1	$2K–$5K
Workpiece modification	None — no pressure head needed	$0
Filtration upgrade	Required (10–20 micron)	$3K–$8K
Total retrofit investment		$15K–$43K

BTA (STS) Retrofit

Component	Required	Approximate Cost
Coolant pump upgrade	Yes (20–60 bar, 100–400 L/min)	$5K–$20K
Rotating pressure head	Yes — seals against workpiece	$8K–$20K
High-pressure hoses	Yes — rated for BTA pressure	$2K–$5K
BTA drill tube	Yes (single-tube)	$3K–$10K
BTA drill heads	Yes (various diameters)	$200–$1,000 each
Chip separation system	Required (internal chip return needs separation)	$5K–$15K
Steady rest(s)	Recommended for > 30:1	$2K–$5K
Workpiece sealing	Required — may need modification	$1K–$5K
Filtration upgrade	Required (10–20 micron)	$3K–$8K
Total retrofit investment		$29K–$88K

Capability Comparison in Retrofit Configuration

Capability	Ejector (DTS)	BTA (STS)	Advantage
Diameter range	18–200 mm	18–250 mm	BTA (larger max)
Max depth ratio	50:1 (typical retrofit)	30:1 (typical retrofit)	Ejector
Penetration rate	4–6× gun drilling	5–7× gun drilling	BTA (marginally faster)
Diameter tolerance (retrofit)	IT9–IT11	IT8–IT10	BTA
Surface finish	Ra 0.8–3.2 µm	Ra 0.8–2.5 µm	BTA
Workpiece face requirement	None — no seal needed	Flat face for pressure head seal	Ejector
Chip evacuation	Venturi suction	Pressure-driven	BTA (more robust)
Coolant pressure needed	20–40 bar	25–60 bar	Ejector (lower)
Compatible with standard lathe?	Yes	Limited (pressure head interference)	Ejector

Cost Comparison Per Hole (Retrofit Scenario)

Assumptions: 25 mm diameter, 1,000 mm deep (40:1), 4140 steel, existing CNC lathe:

Cost Factor	Ejector	BTA
Retrofit investment	$30,000	$60,000
Cycle time	15 min (at 4× gun drilling rate)	12 min (at 5× gun drilling rate)
Tool cost per hole	$0.30	$0.25
Machine rate (existing lathe)	$15/hr	$15/hr
Labor cost per hole	$3.75	$3.00
Total per-hole (operating cost)	$4.05	$3.25
Per-hole savings of BTA	—	$0.80

Break-Even Analysis

Annual Volume	Ejector Total Cost	BTA Total Cost	BTA Payback Period
500 holes	$32,025	$61,625	Never (BTA costs more at this volume)
1,000 holes	$34,050	$63,250	Never
5,000 holes	$50,250	$76,250	20+ years
10,000 holes	$70,500	$92,500	40 years

Conclusion: At any practical production volume, ejector drilling provides a better ROI for CNC lathe retrofit because:

Lower retrofit investment ($30K vs $60K)
No workpiece sealing requirement — no workpiece modification cost
Compatible with all lathe types — no pressure head interference
The 20% cycle time advantage of BTA is too small to offset the $30K investment gap

When BTA Retrofit Makes Sense

Scenario	Rationale
Existing BTA tooling already available	No new tooling investment needed
Very large diameters (> 80 mm)	BTA tooling is more available at this range
Extreme depth ratios required (> 60:1)	BTA’s pressure-driven chip evacuation is more reliable
Workpiece face is flat and consistent	No seal-related modification cost

Decision Framework

Choose Ejector (DTS) Retrofit When:

Diameter 18–80 mm
Retrofit budget < $50K
Workpiece entry face is irregular (casting, forging, rough machining)
Multiple part types with different entry geometries
First deep hole drilling retrofit for the shop
Annual volume < 15,000 holes
Depth ratio < 50:1

Choose BTA (STS) Retrofit When:

Diameter 40–200 mm
Retrofit budget > $50K is acceptable
Workpiece entry face is consistently flat and square
Annual volume > 15,000 holes
Depth ratio > 50:1 (and workpiece can accommodate)
Existing BTA tooling or service support available
Chip evacuation reliability is critical (no Venturi effect to fail)

Summary

For CNC lathe retrofit applications, ejector drilling (DTS) is almost always the better economic choice. The total retrofit investment is typically 40–60% lower than BTA ($30K vs $60K), and ejector drilling imposes fewer constraints on workpiece geometry. The per-hole operating cost of BTA is approximately 20% lower, but the volume required to recover the additional $30K investment is impractically high — typically 40+ years of production. Only in cases where existing BTA tooling is available, diameters are very large, or depth ratios exceed 60:1 does BTA become the preferred retrofit option. For ejector drilling setup details, see setting up ejector drilling on a CNC lathe. For a broader method comparison, see ejector vs BTA vs gun drilling comparison.