Offline Programming & CAM for Deep Hole Drilling Operations

Programming a deep hole operation is not like programming a standard hole. The G-code that works at 3× diameter will break a tool at 15× diameter. The difference is not in the machine or the tool — it is in the strategy encoded in the CAM program.

Offline programming for deep hole drilling requires deliberate decisions about pecking strategy, coolant delivery, feed and speed management, and tool path optimisation that go far beyond standard drilling cycles. This article covers the CAM strategies, G-code techniques, and programming best practices for deep hole drilling operations from 3× to 100× diameter.

Canned Cycles for Deep Hole Drilling ​

G73 — Chip Break Cycle ​

G73 performs a small retract (typically 0.25 mm) at the end of each peck to break the chip without fully exiting the hole:

G99 G73 X10. Y10. Z-50. R2. Q5. F150.

• Best for: Ductile materials (aluminium, low-carbon steel) at depths up to 7× diameter
• Retract: Small increment — chips are broken but not evacuated from the hole
• Risk: Chip packing at depths beyond 5× diameter if coolant pressure is insufficient
• Advantage: Faster than G83, minimal cycle time increase

G83 — Full Retract Peck Cycle ​

G83 retracts completely to the R-plane after each peck, clearing chips and allowing coolant to reach the cutting zone:

G99 G83 X10. Y10. Z-50. R2. Q8. F120.

• Best for: Deep holes exceeding 5× diameter, difficult materials, poor chip evacuation
• Retract: Full retraction to clearance plane or R-plane
• Cycle time: 2–3× longer than G73 for the same peck depth
• Preferred method: When coolant-through tooling is not available

Variable Peck Cycles ​

Standard G73 and G83 use a fixed peck depth (Q value) for the entire hole. Variable peck cycles reduce the peck depth progressively as the hole gets deeper:

; Haas-style variable peck
G83 R2. Z-100. I12. J2. K3. F100.

• I: First peck depth (e.g., 12 mm)
• J: Reduction per subsequent peck (e.g., 2 mm less each peck)
• K: Minimum peck depth (e.g., 3 mm — once reached, peck depth stays constant)

This addresses the physics of deep hole drilling: shallow pecks are adequate near the surface, but deeper holes require smaller pecks to manage chip volume and evacuation.

CAM Software Deep Hole Modules ​

Modern CAM platforms offer dedicated deep hole drilling features that go beyond basic canned cycles.

hyperMILL 2024 (OPEN MIND) ​

The hyperMILL 2024 suite introduced a dedicated deep hole drilling CAM strategy with:

• Process tab: Clear definition of coolant stages, dwell time at depth, and chip-breaking intervals
• Single-tip gun drill simulation: Precise collision checking with detailed stock removal visualisation for gun drilling tools
• Automatic rest material detection: Optimised toolpath calculations for multi-pass operations
• CAM Plan: Topology-based component analysis that produces toolpaths aligned with geometric features

This module is particularly valuable for programming gun drilling operations where the single-lip tool geometry requires accurate collision avoidance and chip load management.

Tebis CAM ​

Tebis offers a complete deep hole drilling solution specific to gun drilling and BTA operations:

• Automatic bore detection: Feature extraction from CAD models, identifying all holes and their properties
• Template-based programming: Parameterised drilling cycles that can be reused across similar operations
• Drill bush library: Tool holder and bushing collision checking for real-world manufacturing constraints
• Dual spindle configuration: Support for machines with multiple drilling spindles
• Quill control: Programmable quill extension for deep hole machines
• Depth capability: Supports programming for holes up to 4,000 mm depth

NX Manufacturing ​

Siemens NX supports deep hole drilling through simulation cycles that use pure G00/G01 motions (no canned cycles):

• Peck drill simulation: Full retract cycle comparable to G83 but output as long-hand code
• Chip break simulation: Reduced retract comparable to G73 but machine-independent
• Advantage: Post-processor independent — works on any machine that reads G00/G01
• Limitation: Generates significantly longer NC programs than canned cycle equivalents

Fusion 360 / Inventor CAM ​

Autodesk's CAM platform supports:

• Guided deep drilling (gun drilling) cycle for specialised tooling
• Chip breaking and deep drilling canned cycles with full parameter control
• Hole feature recognition: Automatic selection of same-diameter holes from solid models
• Feed and speed reduction: Configurable reduction at depth thresholds

Pecking Strategy Design ​

The pecking strategy is the most important programming decision in deep hole drilling.

General Guidelines ​

Peck Strategy by Material ​

Depth-Dependent Parameters ​

A recommended parameter schedule for deep hole drilling in steel (10 mm drill, 200 mm depth):

Custom Cycle Programming ​

When standard canned cycles are insufficient, custom macro programs provide complete control.

Custom G83 with Variable Retract ​

For very deep holes, a custom cycle can vary both peck depth and retract distance:

; Custom deep hole cycle — variable peck, variable retract
O9001 (Deep Hole Cycle)
  #1 = #24 (X position)
  #2 = #25 (Y position)
  #3 = #26 (Z depth)
  #4 = #7 (R retract plane)
  #5 = #9 (Feed rate)
  #20 = #6 (Initial peck depth)
  #21 = #13 (Minimum peck)
  
  G00 Z#4
  WHILE [#3 LT #4] DO1
    G01 Z#4 F#9
    #4 = #4 + #20
    #20 = #20 * 0.85 (Reduce peck by 15%)
    IF [#20 LT #21] THEN #20 = #21
    G00 Z#4 (Full retract)
    G00 Z[#4 - #20 + 0.5] (Rapid to last depth minus safety)
  END1
M99

Depth-Dependent Speed and Feed Control ​

Advanced custom cycles can adjust speeds and feeds based on depth zones, using lookup tables stored in the control's macro variables.

Advantages of Custom Programming ​

• Full retract control: Retract only far enough to clear chips, not to R-plane, saving cycle time
• Adaptive peck depth: Computer-optimised peck schedule based on hole geometry
• Coolant control: Synchronised coolant on/off with peck cycles
• Tool protection: Automatic feed hold or retract on spindle load monitoring

Limitations ​

• Program length: Custom cycles generate significantly longer code than canned cycles
• Portability: Custom macros are machine-specific and may require adaptation for different controls
• Verification: Long-hand code requires thorough simulation to detect programming errors

Tool Path Optimisation ​

In multi-hole deep drilling operations, the sequence of holes significantly affects total cycle time.

Sequence Optimisation ​

The drilling sequence can be modelled as a Traveling Salesman Problem (TSP). Genetic algorithm optimisation reduces non-cutting travel time by 30–50% compared to arbitrary or CAD-order sequencing.

Depth-First vs. Breadth-First ​

• Depth-first: Complete each hole to full depth before moving to the next. Best for deep holes where tool changes are infrequent.
• Breadth-first: Drill all holes to a certain depth, move to the next increment, and repeat. Best for shallow holes requiring frequent tool changes.

For deep holes, depth-first is almost always preferred because it minimises the number of tool approaches and retractions.

Multi-Tool Operations ​

When a deep hole requires multiple tools (centre drill, pilot drill, reamer, thread mill), CAM software should optimise the sequence to minimise tool changes:

• Group by tool: Execute all operations with tool 1, then tool change to tool 2
• Group by hole: Execute all operations on hole 1, then tool change to next hole
• Optimal: Group by tool for deep holes (depth-first within each tool)

Simulation and Verification ​

Deep hole drilling errors are expensive — a broken tool at 20× diameter often means a scrapped workpiece.

Collision Checking ​

Modern CAM platforms provide comprehensive collision detection:

• Tool holder collision: Checks for interference between the tool holder and the workpiece or fixture at full depth
• Drill bushing alignment: Verifies that bushing locations match hole positions for BTA and gun drilling
• Machine kinematics: Full machine model simulation to detect axis limit violations and rotary table interference

Stock Removal Visualisation ​

Single-tip gun drill simulation (available in hyperMILL 2024) shows the material removal process in detail, revealing:

• Uneven stock removal that indicates tool deflection or misalignment
• Burr formation at breakthrough
• Incomplete chip evacuation

G-Code Verification ​

Tools such as MoCoNC offer augmented reality G-code path verification, overlaying the tool path on a live camera image of the workpiece. This allows operators to verify the program against the actual material setup before cutting.

Cimco / Predator Backplotting ​

Standard backplotting tools should be used with attention to:

• Rapid motion verification: Ensure no rapids occur within the hole
• Feed rate consistency: Verify feed reduction at depth
• Retract clearance: Confirm that retract distances are adequate

Material-Specific CAM Parameters ​

Aluminium Alloys ​

Steel (Low-Alloy, 200–300 HB) ​

Stainless Steel (304, 316) ​

Titanium (Ti-6Al-4V) ​

FAQ ​

What is the difference between G73 and G83 for deep hole drilling? ​

G73 (chip break cycle) retracts only a small amount (approximately 0.25 mm) to snap chips without leaving the hole, making it faster but suitable only for ductile materials at moderate depths. G83 (peck drill cycle) retracts fully to the R-plane after each peck, providing complete chip evacuation and coolant access but at 2–3× the cycle time. For depths exceeding 5× diameter, G83 is the safer choice.

How do I program variable peck depths for deep holes? ​

Variable peck depths are programmed using IJK parameters on Haas and compatible controls: I (first peck depth), J (reduction per subsequent peck), and K (minimum peck depth). This creates a decreasing peck schedule that matches the physics of deep hole drilling — larger pecks near the surface, smaller pecks at depth. Controls without IJK support require custom macro programming or long-hand G-code.

Which CAM software supports gun drilling tool paths? ​

hyperMILL 2024 offers dedicated single-tip gun drill simulation and collision checking. Tebis CAM provides a complete deep hole drilling solution with automatic bore detection, template-based programming, and drill bush libraries. Fusion 360 and Inventor CAM support guided deep drilling cycles. These specialised modules handle the unique tool geometry, coolant requirements, and bushing alignment needed for gun drilling operations.

How much can tool path optimisation reduce cycle time? ​

Genetic algorithm-based sequence optimisation (TSP modelling) reduces non-cutting travel time by 30–50% compared to arbitrary hole sequencing. For operations with many holes at the same depth, depth-first sequencing (complete each hole before moving to the next) provides additional time savings by minimising tool approaches and retractions. Total cycle time reduction including cutting time is typically 10–25%.

Should I use depth-first or breadth-first sequencing for deep holes? ​

Depth-first (complete each hole to full depth before moving to the next) is strongly preferred for deep holes. Breadth-first drilling (all holes to partial depth, increment, repeat) multiplies the number of peck cycles and approach moves, increasing cycle time and tool wear. Depth-first is also safer because each hole is completed before swarf from adjacent holes can interfere.

How do I set up a custom peck cycle in Fanuc macro B? ​

Use a WHILE loop with variables for current Z position, peck depth, and feed rate. Each iteration: feed to peck depth, retract to clear chips, reduce peck depth by a factor (e.g., 0.85× per iteration), and repeat until target depth is reached. Store parameters in common variables (#500 series) for easy adjustment by the operator. The key advantage of custom macros is the ability to vary feed rate and spindle speed by depth zone.

What is the CAM strategy for BTA drilling? ​

BTA drilling requires CAM support for external coolant delivery (coolant through the machine/tool holder, not the tool), drill bushings at the hole entrance, and the larger tool diameters typical of BTA (18–200 mm). CAM software should support quill control for machines with limited Z-axis travel and variable bushing positions. Tebis CAM and hyperMILL offer dedicated BTA programming modules. Standard peck cycles are generally not used — BTA drilling is a continuous-feed operation with chip evacuation through the hollow tool interior.

How do I verify a deep hole drilling program before running it? ​

Comprehensive verification requires: (1) collision checking with full machine model and tool holder assembly, (2) G-code backplotting with feed rate verification at all depth zones, (3) stock removal visualisation to confirm even material removal, (4) AR-based verification (such as MoCoNC) to overlay the tool path on the actual workpiece setup, and (5) single-block run with reduced rapid override for the first production part.

Summary ​