G75 Cycle | Grooving and Drilling | Turning

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G75 CNC Code: Mastering Grooving and Peck Drilling in Turning

Introduction:

In CNC turning, machining grooves and efficiently drilling on the face of a workpiece are common operations. The G75 G-code is a versatile canned cycle that, depending on the CNC control system, can be used for either grooving (peck grooving) along the X-axis or peck drilling on the end face of a part (similar to G74, but often with slightly different parameters). This guide provides a detailed explanation of G75, focusing on its primary use in grooving, but also explaining its potential application for face drilling. We’ll cover its function, syntax, applications, variations across control systems (Fanuc, Siemens, Haas, Mazatrol, Mitsubishi, Heidenhain, and others), best practices, troubleshooting, and programming examples. This guide is for all CNC users, from beginners to experienced.

1. What is the G75 G-code? (Primary Function: Grooving)**

On most CNC lathes (particularly those with Fanuc and Fanuc-compatible controls), the G75 command initiates a canned cycle for peck grooving (also sometimes called interrupted cut turning). This is its primary and most common function.

Key Concepts (Grooving):

  • Grooving: Cutting a recess or groove into the outer diameter (OD) or inner diameter (ID) of a cylindrical workpiece. This is distinct from parting off, which is cutting all the way through the workpiece to separate a finished part.
  • Peck Grooving: A grooving technique where the tool makes a series of cuts, retracting slightly after each cut to break chips and allow coolant to reach the cutting zone. This is essential for deep grooves, wide grooves, or materials that produce stringy chips.
  • Canned Cycle: A pre-programmed sequence of operations that simplifies programming.
  • X-Axis Grooving: G75 on lathes is typically used for grooving along the X-axis (radial cuts).
  • Chip Control: Breaking long chips.

2. G75 for Peck Drilling (Secondary Function - Control Dependent)**

On some CNC controls (and this is where a lot of the confusion arises), G75 can also be used for peck drilling on the end face of the workpiece, similar to the G74 cycle. However, this is not universal.

Important Distinction:

  • G74: Is almost always dedicated to end face peck drilling.
  • G75: Is primarily for grooving on lathes. Its use for face drilling is control-system-dependent. Always consult your machine’s manual.

This article will primarily focus on G75’s grooving function, but we’ll mention the drilling aspect where relevant for specific controls.

3. G75 Syntax and Parameters (Grooving - Fanuc Style)**

The syntax for G75 (for grooving) on Fanuc and many compatible controls is typically a two-line format:

First G75 Block:

G75 R[Retract Amount]
  • G75: The G-code for the peck grooving cycle.
  • R[Retract Amount]: Specifies the amount the tool retracts in the cutting axis after each peck. This is a small value (e.g., 0.5 mm or 0.02 inches) and is crucial for chip breaking.

Second G75 Block:

G75 X[Final X Diameter] Z[Final Z Position] P[Peck Depth in X] Q[Incremental Shift in Z] R[Clearance] F[Feed Rate]
  • G75: Again, the G-code.
  • X[Final X Diameter]: The final X-axis diameter of the groove. This defines the depth of the groove.
  • Z[Final Z Position]: The final Z-axis position of the groove. This defines the location of the groove along the length of the workpiece.
  • P[Peck Depth in X]: The incremental depth of each peck in the X-axis (radial direction). This is often specified in microns (or 0.001mm / 0.0001inch) without a decimal point on Fanuc-style controls. For example, P2000 would represent a peck depth of 2.0 mm.
  • Q[Incremental Shift in Z]: The incremental distance the tool moves along the Z-axis between each series of pecks. This defines the width and shape of the groove. Also often specified in microns without a decimal point.
  • R[Clearance]: (Optional on some controls) A clearance amount at the end of the grooving cycle.
  • F[Feed Rate]: The feed rate for the grooving operation.

Example (Fanuc-style, OD Grooving):

N10 T0303 ; Select grooving tool (Tool 3, Offset 3)
N20 G97 S800 M03 ; Constant RPM, spindle on
N30 G00 X60.0 Z5.0 ; Rapid to a safe position

; --- G75 Peck Grooving Cycle ---
N40 G75 R0.5 ; Retract amount 0.5 mm
N50 G75 X20.0 Z-25.0 P2000 Q3000 F0.1 ; Groove to X20, Z-25, peck depth 2mm, Z-shift 3mm, feed 0.1 mm/rev

N60 G00 X60.0 Z5.0 ; Rapid retract
N70 M30 ; Program end

Explanation:

  1. N10-N30: Tool selection, spindle control, rapid to a safe position.
  2. N40 G75 R0.5: Sets the retract amount to 0.5 mm.
  3. N50 G75 X20.0 Z-25.0 P2000 Q3000 F0.1:
  • X20.0: The final diameter of the groove (20 mm).
  • Z-25.0: The final Z-position of the groove (25 mm from the Z-zero point).
  • P2000: The peck depth in X is 2000 microns (2.0 mm).
  • Q3000: The incremental shift in Z is 3000 microns (3.0 mm).
  • F0.1: The feed rate is 0.1 mm/revolution.
  1. The cycle will repeatedly peck in the X-direction (reducing the diameter by 2mm per peck), retract by 0.5mm, move 3mm in Z, and repeat until Z-25 is reached.

4. Control System Variations (Grooving Focus)

  • Fanuc: The two-line format described above is standard.
  • Haas: Very similar to Fanuc.
  • Mitsubishi: Often very similar to Fanuc.
  • Siemens (SINUMERIK):
    • CYCLE93 (Grooving Cycle): Siemens primarily uses CYCLE93 for grooving operations. This is a more comprehensive cycle than G75, allowing for various groove shapes, multiple passes, and finishing allowances.
    • Parameters: CYCLE93 uses a set of parameters to define the groove geometry, cutting depths, etc.
  • Mazatrol (Mazak):
    • Conversational Programming: Grooving is typically defined within the conversational programming interface, as part of the overall machining process. You would select a grooving operation and specify the dimensions, tool, and cutting parameters.
    • BAR OUT: Mazatrol uses BAR OUT in conversational programming.
    • EIA/ISO (G-code): Mazak machines can run standard G-code, and G75 would be similar to Fanuc.
  • Heidenhain:
    • Cycles: Heidenhain uses specific cycles for grooving, not a direct G75 equivalent.
    • Plain Text Programming: Heidenhain’s conversational programming is known for its clarity.
  • Other Controls (Okuma, Fagor, etc.): Consult the specific programming manual.

Key Takeaway: While G75 is a common G-code for grooving on Fanuc and similar controls, many other controls use dedicated cycles (like Siemens’ CYCLE93) or conversational programming methods. Always refer to your machine’s manual.

5. G75 for Face Peck Drilling (Control-Specific)**

As mentioned earlier, some controls use G75 for face peck drilling, similar in function to G74. This is not universal, and you must check your machine’s manual.

  • Fanuc (and similar): On some Fanuc controls, G75 can be used for face peck drilling. The syntax is often similar to the grooving syntax, but the interpretation of the parameters changes. However, G74 is usually the preferred and more clearly defined cycle for face drilling on Fanuc lathes.
  • Syntax (Drilling - Fanuc):
    G75 R...;
G75 X... Z... P... Q... R... F...;
  • Example:
G75 R2
G75 X0 Z-20 P1000 Q3000 R0 F100
  • Other Controls: If your control uses G75 for drilling, the manual will clearly state this and provide the correct syntax and parameter definitions.

6. Best Practices for G75 (Grooving and Drilling, if applicable)**

  • Correct Cycle Selection: Use G75 for grooving (its primary function on most lathes) or for face peck drilling only if your control specifically supports and documents this usage. For face drilling, G74 is generally preferred.
  • Appropriate Peck Depth (P): Choose a peck depth that is appropriate for the material, tool, and groove/hole depth. Too large a peck depth can lead to tool breakage.
  • Appropriate Z-Shift (Q - Grooving): Choose a Z-shift that creates the desired groove width and shape.
  • Retract Amount (R): Ensure the retract amount is sufficient to break chips and allow coolant to reach the cutting zone.
  • Optimize Feed and Speed: Use appropriate feed rates and spindle speeds for the material and operation.
  • Use Coolant: Use appropriate coolant.
  • Verify the Toolpath: Always simulate your program.
  • Correct Tool Type: Select grooving tools for G75.
  • Check Machine Manual: Always refer to machine’s manual.

7. Troubleshooting Common G75 Problems

  • “Sequence Number Not Found” Alarm (Grooving):
    • Cause: Incorrect P or Q values (if used). This is more relevant to G71, G72, and G73, which require P and Q.
    • Solution: Double-check the P and Q values (if applicable).
  • “Illegal Argument” or “Invalid G-Code” Alarm:
    • Cause: Syntax errors or unsupported parameters.
    • Solution: Consult your machine’s manual and review the G75 syntax.
  • Incorrect Groove/Hole Dimensions:
    • Cause: Incorrect parameter values (X, Z, P, Q), incorrect tool offsets.
    • Solution: Double-check all parameters and offsets.
  • Tool Breakage:
    • Cause: Excessive peck depth, feed rate too high, dull tool, inadequate coolant.
    • Solution: Reduce peck depth/feed rate, use a sharper tool, ensure adequate coolant.
  • Poor Surface Finish:
    • Cause: Excessive peck depth, incorrect feed and speed.
    • Solution: Reduce depth and adjust parameters.

8. Troubleshooting Common G75 Problems

  • “Illegal Argument” or “Invalid G-Code” Alarm:
    • Cause: Syntax errors or unsupported parameters.
    • Solution: Consult your machine’s manual and review the G75 syntax.
  • Incorrect Groove/Hole Dimensions:
    • Cause: Incorrect parameter values (X, Z, P, Q), incorrect tool offsets.
    • Solution: Double-check all parameters and offsets.
  • Tool Breakage:
    • Cause: Excessive peck depth, feed rate too high, dull tool, inadequate coolant.
    • Solution: Reduce peck depth/feed rate, use a sharper tool, ensure adequate coolant.
  • Poor Surface Finish:
    • Cause: Excessive peck depth, incorrect feed and speed.
    • Solution: Reduce depth and adjust parameters.
  • Chips Not Breaking:
    • Cause: Retract distance is not enough.
    • Solution: Check R value.

9. Complete Example Program: G75 for OD Grooving (Fanuc Style)

This example demonstrates using G75 to create a series of grooves on the outer diameter of a workpiece:


O0003 (G75 OD Grooving Example)

; --- Tool Setup ---
T0303 ; Select grooving tool (Tool 3, Offset 3)

; --- Work Offset ---
G54 ; Select Work Coordinate System 1

; --- Spindle and Coolant ---
G97 S800 M03 ; Constant RPM, spindle on clockwise
M08 ; Coolant on

; --- Define Groove Parameters ---
; Groove 1: Z-20, Width = 5mm, Depth (X) = 5mm (from starting diameter)
; Groove 2: Z-40, Width = 5mm, Depth (X) = 5mm
; Groove 3: Z-60, Width = 5mm, Depth (X) = 5mm
; Starting Diameter: 60mm

; --- Rapid to Safe Start Position ---
G00 X70.0 Z5.0 ; Outside and clear of the workpiece

; --- Groove 1 ---
N10 G75 R0.5 ; Retract amount 0.5mm
N20 G75 X50.0 Z-20.0 P1000 Q5000 F0.1 ; Groove 1 (X50 = 60 - 2*5)

; --- Groove 2 ---
N30 G75 R0.5
N40 G75 X50.0 Z-40.0 P1000 Q5000 F0.1 ; Groove 2

; --- Groove 3 ---
N50 G75 R0.5
N60 G75 X50.0 Z-60.0 P1000 Q5000 F0.1 ; Groove 3

; --- Retract and End ---
N70 G00 X70.0 Z5.0 ; Rapid to safe position
N80 M30 ; Program end

Explanation of the Complete Example:

  • Tool Setup: The program uses a grooving tool (T03).
  • Work Offset: G54 is used.
  • Spindle/Coolant: The spindle is started in constant RPM mode (G97), and coolant is turned on.
  • Safe Start: The tool rapids to a safe position (X70.0 Z5.0) that is outside the starting diameter of the workpiece and clear of the face.
  • Groove 1 (N10-N20):
    • N10 G75 R0.5: Sets the retract amount to 0.5 mm. This is the amount the tool will retract in X after each peck.
    • N20 G75 X50.0 Z-20.0 P1000 Q5000 F0.1: Executes the G75 cycle for the first groove.
      • X50.0: The final diameter of the groove. The starting diameter is assumed to be the current X position (which is X70.0 from the rapid move). The groove depth is (70-50)/2 = 10mm.
      • Z-20.0: The Z-axis position of the groove.
      • P1000: The peck depth in X is 1000 microns (1.0 mm).
      • Q5000: The incremental shift in Z is 5000 microns (5.0 mm). This defines the width of the groove.
      • F0.1: The feed rate.
  • Groove 2 (N30-N40) and Groove 3 (N50-N60): The G75 cycle is repeated for the second and third grooves. Only the Z coordinate changes, defining the location of each groove along the Z-axis.
  • Retract and End (N70-N80): The tool rapids to a safe position, and the program ends.

Key Points about this Example:

  • Multiple Grooves: This example demonstrates how to create multiple grooves using G75. You simply repeat the G75 command with different X and Z values for each groove.
  • Peck Depth (P): The P value (peck depth in X) is relatively small (1mm). This is appropriate for grooving, as it helps to break chips and prevent tool overload.
  • Z-Shift (Q): The Q value determines the width of the groove.
  • Retract (R): The R value provides a small retract after each peck, improving chip clearance.
  • Starting Position: The tool must be positioned outside the final diameter of the groove before the G75 cycle begins.

This complete example, along with the preceding explanations, should give you a thorough understanding of how to use the G75 command for peck grooving in CNC turning. Remember to always consult your machine’s manual for the specific implementation details for your control system.

10. Conclusion: Versatile Grooving and (Sometimes) Drilling

The G75 G-code is a versatile tool in CNC turning, primarily used for peck grooving operations. It provides an efficient way to create grooves of varying depths and widths, with the added benefit of chip breaking through the retract motion. On some controls, G75 can also be used for face peck drilling, although G74 is often the more dedicated command for that purpose. Understanding the specific implementation of G75 on your CNC control system, and adhering to best practices, is crucial for successful and safe machining.