Deep Hole Drilling on CNC Lathes: Setup and Programming

Deep hole drilling on a CNC lathe is not the same as drilling on a dedicated machine. The lathe's live tooling spindle has limited power and speed, the toolholder must share turret space with turning tools, and the coolant system was designed for chip breaking, not for hydraulic chip transport. Yet the ejector system makes it possible — and with the right setup, a lathe can drill holes that rival dedicated machine quality.

Overview ​

Deep hole drilling on CNC lathes with live tooling is an alternative to dedicated deep hole drilling machines. It is most practical when the workpiece requires both turning and deep hole operations in a single setup, or when production volume does not justify a dedicated machine.

Machine Requirements ​

Minimum Specifications ​

Lathe Type Comparison ​

Live Tooling Limitations ​

Toolholding and Workholding ​

Toolholder Types ​

For deep hole drilling, the toolholder must:

• Support through-spindle coolant at the required pressure without leaks
• Provide concentric clamping within 0.005 mm TIR
• Accommodate the drill tube diameter with a suitable bushing or collet

Workholding ​

The workpiece must be held concentrically within 0.02 mm TIR at the drilling face. Higher runout causes:

• Drill wander at entry (bell-mouth)
• Oversized holes
• Uneven guide pad loading (accelerated wear)

Tailstock and Steady Rests ​

Guide Bushing and Pilot Hole Requirements ​

Guide Bushings for Gun Drilling ​

When gun drilling on a lathe, a guide bushing is essential:

The guide bushing can be mounted in the turret adjacent to the gun drill, or as a separate bushing holder in the turret station.

Pilot Hole Requirements ​

The pilot hole must be concentric with the spindle axis within 0.005 mm and have the same point angle as the deep hole drill. A mismatched point angle causes the drill to deflect at the pilot-to-full-hole transition.

Allied Machine 6-Step Process ​

Coolant System Requirements ​

The coolant system is the most critical factor for deep hole drilling on a lathe.

Pressure Requirements ​

High-Pressure Coolant Options ​

Filtration ​

Insufficient filtration causes:

• Coolant channel blockage in gun drills (tool failure)
• Accelerated guide pad wear from abrasive particles
• Surface finish degradation
• Seal failure in the rotary union

Canned Cycles for Live Tooling ​

Face Drilling (G83) ​

G83 is the standard peck drilling cycle for face (Z-axis) drilling with live tooling:

M51                 ; C-axis indexing mode ON
G00 X0 C0 Z20      ; Position to hole center
M03 S5000          ; Start live spindle
G83 X0 C0 Z-80 R-10 Q3000 P500 F15 M31  ; Drill 80 mm deep
G80                ; Cancel cycle

Radial Drilling (G87) ​

G87 is the peck drilling cycle for radial (X-axis) drilling with live tooling:

M51                 ; C-axis indexing mode ON
G00 Z0 C0 Z20      ; Position to hole center
M03 S5000          ; Start live spindle
G87 Z0 C0 X-50 R5 Q2000 P500 F12 M31  ; Drill 50 mm radial
C90 M31            ; Index to 90°, drill
C180 M31           ; Index to 180°, drill
C270 M31           ; Index to 270°, drill
G80                ; Cancel cycle

Peck Retraction Types ​

For deep hole drilling, use full retraction (G83/G87 style) to ensure chip evacuation from the flutes.

Custom Deep Hole Programming Techniques ​

Standard peck cycles have limitations for deep hole drilling. Custom macro programs can implement more sophisticated strategies.

Variable Peck Depth Cycle ​

(DEEP HOLE CYCLE WITH VARIABLE PECK)
(USAGE: G65 P8000 A_depth B_first_peck C_max_peck D_min_peck 
       F_feed R_retract Z_start)
O8000
  #1 = #1  (total depth A)
  #2 = #2  (first peck B)
  #3 = #3  (max peck C)
  #4 = #4  (min peck D)
  #9 = #9  (feed F)
  #18 = #18 (retract R)
  #26 = #26 (Z start)
  
  #30 = #26  (current Z)
  #31 = #2   (current peck)
  
  WHILE [#30 GT #1] DO1
    #30 = #30 - #31
    IF [#30 LT #1] THEN #30 = #1
    G01 Z#30 F#9
    G00 Z#18
    G00 Z[#30 + 1.0]
    #31 = #31 * 1.1
    IF [#31 GT #3] THEN #31 = #3
  END1
M99

Peck Strategy Comparison ​

Programming for Ejector (DTS) on a Lathe ​

The ejector system is the most practical BTA-class method for CNC lathes because it requires no pressure head seal.

Setup Requirements ​

Sample Program ​

(EJECTOR DRILLING CYCLE)
M51                    ; C-axis engage
G00 X0 Z50            ; Position to start
M03 S2000             ; Start spindle
M08                   ; Coolant ON (through-spindle)
G01 Z60 F200          ; Rapid feed to workpiece entry
G01 Z-300 F30         ; Feed to full depth
G00 Z50               ; Retract
M09                   ; Coolant OFF
M05                   ; Spindle stop
M155                  ; C-axis disengage

Ejector drilling does not typically require peck cycles because the continuous chip evacuation through the inner tube handles chips as they are produced. However, if chip packing occurs, a peck cycle can be added.

Setup Procedure ​

Step-by-Step Setup ​

First Article Inspection ​

Common Mistakes and Troubleshooting ​

Summary ​

FAQ ​

Can I gun drill on a standard CNC lathe? ​

Yes, but with limitations. Gun drilling on a standard CNC lathe requires: (1) through-spindle coolant at 10–35 MPa — most standard lathes provide 1–3 MPa, so a high-pressure booster pump is typically needed; (2) a guide bushing mounted in the turret or a bushing holder; (3) a pilot hole 1–2 diameters deep with the same point angle as the gun drill; (4) a stable workholding setup with less than 0.02 mm runout. The ejector (DTS) system is a more practical option for lathes because it operates at lower pressure and does not require a workpiece seal.

What is the deepest hole I can drill on a CNC lathe with live tooling? ​

The maximum depth depends on the method: conventional peck drilling reaches L/D 20:1, parabolic flute drills reach L/D 30:1, gun drilling reaches L/D 100:1 or more with proper support, and ejector drilling reaches L/D 80:1. The limiting factors are drill rigidity, coolant pressure, and chip evacuation. For depths exceeding L/D 50:1, steady rests along the drill tube and workpiece support become necessary.

What are the G-code differences between face and radial live tool drilling? ​

Face drilling (Z-axis) uses G83 with X and C coordinates for hole position. Radial drilling (X-axis) uses G87 with Z and C coordinates. Both cycles support peck parameters (Q), dwell (P), and C-axis clamp M-codes. On Fanuc controls, parameter 5101#2 selects between partial retraction (high-speed peck, G73-style) and full retraction (G83-style). Full retraction is recommended for deep holes where chip evacuation is critical.

Do I need a pilot hole for deep hole drilling on a lathe? ​

For conventional twist drills with L/D < 10:1, a pilot hole is optional — a spot drill is sufficient. For L/D > 10:1, a pilot hole 1–2 diameters deep is strongly recommended. For gun drilling and ejector drilling, a pilot hole is required. The pilot drill should have the same point angle as the deep hole drill. A mismatched point angle causes the drill to deflect during the transition from the pilot hole to the full-depth cut.

What coolant pressure do I need for deep hole drilling on a lathe? ​

Standard through-spindle coolant (1–3 MPa) is adequate for peck drilling up to L/D 20:1 with coolant-through drills. For L/D 20–30:1 with parabolic drills, 3–5 MPa is recommended. For ejector drilling, 2–8 MPa is typical. For gun drilling, 10–35 MPa is required. Most standard lathes need a high-pressure coolant upgrade for gun drilling or ejector drilling.

Is the ejector system better than gun drilling for CNC lathes? ​

For most lathe applications, yes. The ejector (DTS) system offers two key advantages: (1) it operates at lower coolant pressure (2–8 MPa vs. 10–35 MPa for gun drilling), making it compatible with standard lathe coolant systems or moderate upgrades; (2) it requires no pressure head seal against the workpiece, simplifying setup and fixture design. The trade-off is a larger minimum diameter (approximately 18 mm vs. 3 mm for gun drilling) and looser tolerances (IT9–IT11 vs. IT7–IT9).

How do I prevent chip packing in deep holes on a lathe? ​

Chip packing is prevented by: (1) using full-retraction peck cycles (G83/G87 with 5101#2 = 1 on Fanuc) rather than partial retraction; (2) ensuring adequate coolant flow and pressure to flush chips from the cutting zone; (3) reducing feed rate if stringy chips are produced; (4) for gun drilling, verifying that the coolant channel is clear and the chip flute is not blocked; (5) for ejector drilling, checking that the ring nozzle is generating sufficient suction. If packing persists, increase peck frequency and retraction distance.

What are the limitations of live tool spindles for deep hole drilling? ​

Live tool spindles have lower power (3–7 kW) and lower stiffness than main spindles or VMC spindles. Bearing wear is accelerated by continuous high-pressure coolant and high thrust loads. RPM is typically limited to 4,000–8,000 RPM, which restricts cutting speed for small-diameter drills. Heat buildup during continuous drilling can cause bearing failure — aim to limit continuous drilling to under 30 minutes per cycle. Through-spindle coolant helps but may not be available in all live tool holders.

Can I use BTA (STS) drilling on a CNC lathe? ​

BTA (STS) drilling is not practical on standard CNC lathes because it requires a pressure head (BOZA) that seals against the workpiece face. The BOZA must be aligned with the spindle axis, and the workpiece must have a flat, concentric sealing surface. This level of integration is standard on dedicated BTA machines but difficult to achieve on a lathe. The ejector (DTS) system is the BTA-compatible method for lathes.

What is the best workholding method for deep hole drilling on a lathe? ​

A collet chuck (hydraulic or manual) provides the best concentricity for round bar stock. For irregular parts, a set-tru 3-jaw chuck with dial indicator adjustment is recommended. In all cases, indicate the workpiece face at the drilling location and verify runout is below 0.02 mm. For long workpieces (L/D > 10:1), add a steady rest or tailstock support to prevent deflection. For through-hole drilling with a tailstock, use a live center with the OD turned concentrically to the bore axis.

Deep hole drilling on CNC lathes requires careful setup, appropriate coolant pressure, and correct programming. The parameters and recommendations in this article represent typical practice as of 2026. Always verify machine specifications and limitations before attempting deep hole drilling operations on a lathe.