G74 Cycle | End Face Peck Drilling | Turning

[Hakan]

G74 CNC Code: Mastering End Face Peck Drilling on Lathes

Introduction:

Drilling holes on the end face of a workpiece in CNC turning presents unique challenges, especially when dealing with deep holes or materials that produce long, stringy chips. The G74 End Face Peck Drilling Cycle is a specialized canned cycle designed to address these challenges, providing a safe, efficient, and reliable method for drilling on the face of a turned part. This guide provides an in-depth explanation of G74, covering its function, syntax, applications, variations across control systems (Fanuc, Siemens, Haas, Mazatrol, Mitsubishi, Heidenhain, and others), best practices, troubleshooting, and programming examples. This article is designed for CNC machinists and programmers of all skill levels, from beginners to advanced users.

1. What is the G74 End Face Peck Drilling Cycle?

G74 is a G-code command that initiates a canned cycle for peck drilling on the end face of a workpiece in CNC turning. Peck drilling is a drilling technique where the tool drills to a certain depth, retracts slightly (or completely) to break chips and allow coolant to reach the cutting zone, and then drills deeper. This process is repeated until the final depth is reached.

Key Concepts:

• Peck Drilling: A drilling method that involves incremental drilling with periodic retractions.
• Canned Cycle: A pre-programmed sequence of operations that simplifies programming.
• End Face: The flat surface at the end of a cylindrical workpiece, perpendicular to the axis of rotation (Z-axis).
• Chip Breaking: The process of breaking long, continuous chips into smaller, more manageable pieces.
• Chip Evacuation: The process of removing chips from the hole.
• Coolant: A fluid used to cool and lubricate the cutting tool and workpiece.

2. Why Use G74 (Peck Drilling)? The Benefits

Peck drilling (and therefore G74) is essential for many drilling operations on a CNC lathe:

• Improved Chip Control: The retract motion breaks the chips, preventing them from becoming long and tangled, which can damage the tool, the workpiece, and the machine.
• Better Chip Evacuation: The retraction allows chips to be cleared from the hole, preventing clogging and recutting of chips.
• Reduced Heat Buildup: The retract motion allows coolant to reach the cutting zone more effectively, reducing heat buildup and extending tool life.
• Deeper Holes: Peck drilling is essential for drilling deep holes, where chip evacuation and heat buildup are major concerns.
• Harder Materials: Peck drilling is often necessary when drilling harder materials that generate more heat and tougher chips.
• Reduced Tool Wear and Breakage: By preventing chip clogging and reducing heat, peck drilling significantly reduces the risk of tool wear and breakage.
• Improved Hole Quality: Peck drilling results in better hole straightness, roundness, and surface finish.
• Preventing Work Hardening: Heat generation can be prevented by using G74.

3. G74 Syntax and Parameters

The syntax of the G74 command can vary slightly between control systems, common format are used :

Two-Line Format (Fanuc and compatible):

G74 R[Retract Amount];
G74 X[Hole Center X] Z[Final Depth] P[Peck Depth in X] Q[Peck Depth in Z] R[X-axis Finish Allowance] F[Feed Rate];

Let’s break down the parameters:

• G74: The G-code for the end face peck drilling cycle.
• R[Retract Amount]: (First line, both formats) This specifies the retract amount after each peck. This is a small movement, just enough to break the chip. Crucially, on many modern controls, this R value represents a position, relative to the starting Z, that the tool retracts to, NOT the actual distance of retraction.
• X[Hole Center X]: (Second line) The X-coordinate of the center of the hole being drilled. On a lathe, this is often X0 for a hole drilled on the centerline. If drilling off-center holes (using live tooling), you would specify the appropriate X-coordinate.
• Z[Final Depth]: (Second line) The final Z-depth of the hole, measured from the workpiece zero point.
• P[Peck Depth in X]: (Second line) The depth of cut along the X-axis. It is defined without a sign, as a radius value. This parameter is used for side drilling/milling with live tooling.
• Q[Peck Depth in Z]: (Second line) The incremental depth of each peck (in microns or 0.001mm/.0001inch, without a decimal point on many Fanuc-style controls). For example, Q2000 would represent a peck depth of 2.0 mm (or 0.2" in inch mode without a decimal point). This is the most important parameter for controlling the pecking action.
• R[X-axis Finish Allowance/Clearance]: (Second line) In one line format, this R defines clearance distance. In the two-line format, this ‘R’ has different meaning than the ‘R’ in the first line. It often represents a finishing allowance, or clearance amount in X axis.
• F[Feed Rate]: The feed rate for the drilling operation (usually in mm/min or inches/min, or mm/rev or inches/rev, depending on G98/G99 setting).

Important Notes:

• Units: Be absolutely certain of the units used by your control for the Q (peck depth) parameter. On many Fanuc-style controls, it’s in microns (or 0.001mm / 0.0001inch) without a decimal point.
• Retract Amount (R): The behavior of the R value (first line) can vary. On some controls, it’s a small incremental retract. On others, it’s a position to retract to. Consult your manual.
• X-axis Value: For holes drilled on the centerline of the part (the most common case), the X value will often be X0.
• Control-Specific Variations: Always check the manual.

4. Control System Variations

The implementation of G74, while conceptually similar, has significant variations between control systems:

• Fanuc:

  • G74 R...; G74 X... Z... P... Q... R... F...;
  • Q Value: Typically in microns (or 0.001mm) without a decimal point. This is a very common source of errors.
  • R Value (First Line): Often represents a retract position.
  • Widely Used: The Fanuc implementation is very common.

• Siemens (SINUMERIK):

  • CYCLE83 (Deep Hole Drilling): Siemens uses CYCLE83 for deep hole drilling, which includes pecking functionality. There isn’t a direct G74 equivalent in the same way as Fanuc.
  • Parameters: CYCLE83 has many parameters to control the drilling process, including peck depth, dwell times, retraction amounts, and different pecking strategies (chip breaking vs. chip removal).
  • ShopTurn: Siemens’ conversational interface simplifies the programming of drilling cycles.

• Haas:

  • Syntax: Very similar to Fanuc (usually the one-line format).
  • Intuitive Interface: Haas controls are known for their user-friendliness.

• Mazatrol (Mazak):

  • Conversational Programming: Peck drilling is typically defined within the conversational programming interface, as part of the drilling operation. You wouldn’t usually write a G74 command directly. You would select a drilling cycle and specify parameters like peck depth and retract amount.
  • POINT M/C: Mazatrol uses point machining unit for drilling cycles.
  • EIA/ISO (G-code): Mazak machines can run standard G-code, and G74 would be used similarly to Fanuc.

• Mitsubishi:

  • Syntax: Similar to Fanuc.
  • Parameters: May have additional parameters or settings.

• Heidenhain:

  • CYCLE 205 (Universal Peck Drilling): Heidenhain uses CYCLE 205 for universal peck drilling. This cycle offers a wide range of options for controlling the pecking behavior.
  • Plain Text Programming: Heidenhain’s conversational programming is known for its clear and intuitive structure.

• Other Controls (Okuma, Fagor, etc.): Consult the specific programming manual.

Key Takeaways:

• Fanuc is the most common reference: The G74 command is often associated with Fanuc-style syntax.
• Siemens and Heidenhain use dedicated cycles: These cycles offer more advanced features and flexibility.
• Mazatrol is conversational: Peck drilling is handled within the conversational programming environment.
• Always consult your machine’s manual! This is absolutely essential.

5. Programming Examples

Example 1:

O0001 (G74 Example - Centerline Drilling)
T0101 ; Select Tool 1 (Drill)
G90 G21 ; Absolute, metric
G97 S1000 M03 ; Constant RPM, spindle on
G00 X0 Z5.0 ; Rapid to safe position

; --- G74 Peck Drilling Cycle ---
G74 R1.0 ; Retract position 1mm from Z start point
G74 Z-25.0 Q5000 F0.1 ; Drill to Z-25, peck depth 5mm (Q5000 = 5.0mm), feed 0.1 mm/rev

G00 Z5.0 ; Rapid retract
M30 ; Program end

Explanation:

• T0101: Selects the drill (Tool 1) and activates its offset.
• G90 G21: Absolute programming, metric units.
• G97 S1000 M03: Constant RPM mode, spindle on at 1000 RPM.
• G00 X0 Z5.0: Rapids to a safe position near the workpiece face (X0 for centerline drilling).
• G74 R1.0: Specifies that before drilling, tool will be positioned 1mm away from the Z starting point.
• G74 Z-25.0 Q5000 F0.1: This is the core G74 command:
  • Z-25.0: The final depth of the hole (25mm deep).
  • Q5000: The peck depth is 5000 microns (5.0 mm). Note the lack of a decimal point!
  • F0.1: The feed rate is 0.1 mm/revolution.
• G00 Z5.0: Rapidly retracts the tool.
• M30: Ends the program.

Example 2:

O0002 (G74 Example - Two-Line Format)
T0101
G90 G21
G97 S1000 M03
G00 X0 Z5.0

; --- G74 Peck Drilling Cycle ---
G74 R1.0 ; Retract amount 1.0 mm
G74 X0 Z-25.0 P0 Q5000 F0.1 ; Drill to Z-25, peck depth 5mm (Q5000 = 5.0mm), feed 0.1 mm/rev (X is optional for centerline)

G00 Z5.0
M30

Example 3: Siemens CYCLE83 (Conceptual Consult Manual)

; (Siemens CYCLE83 Example - Conceptual)
T01 D1 ; Select Tool 1
G90 G21
G97 S1000 M3
G00 X0 Z5.0

; --- CYCLE83 Deep Hole Drilling ---
CYCLE83(5, 0, 1, -25, , 0, 5, , , 1, , , 0.1, 0, 1) ; Many parameters control the cycle

G00 Z5.0
M30

Note: The exact parameters for CYCLE83 will vary depending on the specific Siemens control. This is a simplified example to illustrate the concept.

Example 4: G74 Off-Center Drilling (Live Tooling on a Lathe - Conceptual)

; (G74 Example - Off-Center Drilling with Live Tooling - Conceptual)
T0505 ; Select live tool (e.g., a drill in a radial live tool holder)
G90 G21 G17 ; Absolute, metric, XY plane (for milling)
G00 X20.0 Y0.0 C0.0 Z5.0 ; Position for drilling (X20.0 is the hole center)
; ... (Possibly activate C-axis indexing) ...

; --- G74 Peck Drilling Cycle ---
G74 R1.0
G74 X20.0 Z-15.0 Q3000 F0.08 ; Drill the hole (Z is the drilling axis)

G00 Z5.0
; ... (Possibly deactivate C-axis indexing) ...
M30

8. Best Practices for Using G74

• Choose an Appropriate Peck Depth (Q): The peck depth should be based on the material being drilled, the drill diameter, and the machine’s capabilities. A general guideline is 1-3 times the drill diameter, but this can vary. Start with a smaller peck depth and increase it if chip evacuation is good.
• Use a Safe Retract Amount (R): Ensure the retract amount is sufficient to break the chips and allow coolant to reach the cutting zone.
• Optimize Feed Rate (F): Use an appropriate feed rate for the material and drill diameter.
• Use Coolant: Use coolant to cool the tool and workpiece and to aid in chip evacuation.
• Verify the Toolpath: Always simulate your program (including the G74 cycle) to visually check the toolpath.
• Correct Tool Type: Select drilling tools.
• Check Machine Manual: Check your machine’s manual.

9. Troubleshooting Common G74 Problems

• “Illegal Argument” or “Invalid G-Code” Alarm:
  • Cause: Syntax errors or unsupported parameters.
  • Solution: Consult your machine’s manual.
• Tool Breakage:
  • Cause: Excessive peck depth, feed rate too high, dull tool, inadequate coolant, or material issues.
  • Solution: Reduce peck depth and/or feed rate, use a sharper tool, ensure adequate coolant flow, and check material properties.
• Poor Hole Quality (Roughness, Out-of-Roundness):
  • Cause: Excessive peck depth, incorrect feed rate, tool runout, or machine vibration.
  • Solution: Reduce peck depth, adjust feed rate, check tool runout, and ensure machine stability.
• Chips Not Breaking:
  • Cause: Retract distance is not enough.
  • Solution: Check R value.

10. Conclusion: Efficient and Safe Drilling on the Face

The G74 End Face Peck Drilling Cycle is a valuable tool for CNC turning, providing a safe and efficient way to drill holes on the end face of a workpiece, especially deep holes or holes in materials that produce difficult chips. By understanding its parameters, variations between control systems, and best practices, you can significantly improve your drilling operations on a CNC lathe, reduce tool wear, and produce high-quality parts.