Setting Up Ejector Drilling on a CNC Lathe

Setting Up Ejector Drilling on a CNC Lathe

The primary advantage of ejector drilling (DTS) over BTA drilling is that it can be retrofitted onto standard CNC lathes and machining centers. No dedicated deep hole drilling machine is required — just a coolant system upgrade, a boring bar support system, and the right tooling.

This guide covers everything needed to set up ejector drilling on a CNC lathe, from coolant system specifications to first-piece inspection.

What You Need

Minimum Requirements

Coolant System

The coolant system is the most important part of the DTS retrofit. Without adequate flow and pressure, the Venturi effect will not work and chip evacuation will fail.

Pump Selection

Important: Flow rate is more critical than pressure in ejector drilling. The Venturi effect requires a specific minimum flow to generate suction. A pump that achieves 40 bar at 20 L/min will not work — you need both.

Filtration

• Minimum: 20 micron absolute
• Recommended: 10 micron for ejector drilling
• Why: The Venturi slots in the drill head are narrow (1–3 mm) and can be blocked by particles. Finer filtration extends Venturi life.

Coolant Type and Temperature

• Type: High-EP emulsion at 8–12% concentration (if machine uses common coolant for all operations)
• Type (dedicated): Neat cutting oil for maximum tool life
• Temperature: 30–40°C; install a chiller if production volume exceeds 500 holes/week
• Monitoring: Install a flow meter and pressure gauge at the coolant swivel input

Coolant Swivel Installation

The coolant swivel transfers coolant from the stationary machine supply to the rotating boring bar.

Mounting Options

Swivel Installation Steps

1. Mount the swivel to the selected location using the manufacturer’s mounting bracket
2. Connect coolant supply from pump to swivel using high-pressure hose (rated for minimum 60 bar)
3. Install pressure gauge at the swivel inlet — this is your reference point for monitoring
4. Connect boring bar to the swivel output; torque to manufacturer specification
5. Check alignment — the swivel bore must be concentric with the spindle axis within 0.03 mm TIR

Swivel Maintenance

Boring Bar Support

The DTS boring bar is longer and less rigid than a BTA tube. Proper support is essential for straight holes and tool life.

Support Configuration

Steady Rest Setup

1. Position the steady rest as close to the workpiece as possible without interfering with the chuck
2. Adjust the pads to contact the boring bar with light pressure — enough to support but not enough to deflect
3. Check alignment — the steady rest center must be concentric with the spindle axis within 0.02 mm TIR
4. Apply lubricant to the boring bar contact surface if using fixed pads

Workpiece Preparation

Ejector drilling does not require a pressure head seal, but proper workpiece preparation still matters.

1. Face the workpiece entry — a faced surface improves pilot hole accuracy
2. Drill pilot hole — depth 1.5–2× D, diameter D + 0.1–0.3 mm, concentricity < 0.02 mm TIR
3. Chamfer the pilot hole entry — 30–45° chamfer prevents edge chipping at entry
4. Clear the exit — for through-holes, ensure at least 2× D clearance behind the workpiece

Programming for Ejector Drilling on a CNC Lathe

G-Code Sequence

; Ejector drilling cycle on a CNC lathe
; Tool: DTS boring bar in coolant swivel
; Ø40 mm × 600 mm deep in 4140 steel

N10 G54 G00 X0 Z5         ; Position to hole center, 5mm from face
N20 G00 X0 Z-2             ; Advance to pilot hole entry
N30 M08                     ; Coolant ON (high-pressure coolant)
N40 G04 P2                  ; Wait 2 seconds for coolant stabilization
N50 G97 S637 M03            ; Spindle ON, 637 RPM (80 m/min)
N60 G01 Z-600 F0.18         ; Feed to depth at 0.18 mm/rev (115 mm/min)
N70 G00 Z5                  ; Rapid retract
N80 M09                     ; Coolant OFF

Important: Always start coolant before spindle rotation. The Venturi effect must be established before cutting begins.

Feed Optimization

• Entry feed: 50% of normal for first 2–3 mm
• Full feed: Programmed feed rate after entry
• Exit feed (through-holes): 50% for last 5–10 mm before breakthrough

First-Piece Inspection Protocol

Before Drilling

• Coolant pressure at swivel verified (≥ minimum for diameter)
• Coolant flow rate verified (≥ minimum for diameter)
• Swivel alignment checked (< 0.03 mm TIR)
• Boring bar support aligned (< 0.02 mm TIR)
• Pilot hole depth, diameter, and concentricity checked
• Tool inspected (inserts, guide pads, Venturi slots)
• Feed and speed set per parameters
• Coolant flow established (visual check at drill head)

After First Hole

1. Withdraw and inspect tool — Check inserts for chipping, guide pads for scoring, Venturi slots for blockage
2. Measure bore — Diameter at entry, 25%, 50%, 75%, and exit
3. Check surface finish — Profilometer at entry, mid-point, exit
4. Check chip condition — Short C-shaped chips indicate good parameters
5. Verify coolant return — Check that chip flow was continuous throughout the cut

Common Setup Mistakes

Upgrading an Existing CNC Lathe: Cost Estimate

This is approximately 10–20% of the cost of a dedicated BTA machine, and 40–60% of the cost of a CNC gun drilling retrofit. Ejector drilling is the lowest-cost path to deep hole drilling capability.

Summary

Setting up ejector drilling on a CNC lathe requires a high-pressure coolant system upgrade, a coolant swivel, DTS boring bar with drill head, and steady rest support for the bar. The total investment is typically $20,000–$40,000 — far less than a dedicated BTA or gun drilling machine. The key to success is adequate coolant flow (not just pressure), proper boring bar support, and correct entry technique. With proper setup, a retrofitted CNC lathe can achieve penetration rates approaching those of dedicated BTA machines at a fraction of the capital cost.

For process fundamentals, see how ejector drilling works. For parameter selection, see ejector drilling parameters guide. For a complete overview, visit the ejector drilling guide.