CNC Canned Turning Cycles: G71, G72, G73, G70 Complete Roughing & Finishing Guide
Canned turning cycles simplify roughing and finishing operations on CNC lathes.
These cycles automatically control tool passes, depth of cut, feed, and finish allowance — allowing you to machine profiles efficiently and safely.
📌 1. Overview of Common Turning Cycles
| G-Code | Function | Description |
|---|---|---|
| G70 | Finishing | Finishes profile after roughing |
| G71 | Roughing | Axial stock removal (Z direction) |
| G72 | Facing | Radial stock removal (X direction) |
| G73 | Pattern repeating | Repeats small patterns with limited retracts |
📌 2. G71 — Rough Turning Cycle (Z-axis)
This cycle removes bulk material along the Z-axis, following a defined contour between two sequence numbers.
Basic Format:
G71 U(Depth of Cut) R(Retract)
G71 P(Start Block) Q(End Block) U(Finish Allowance X) W(Finish Allowance Z) F(Feed)Example:
%
O8001 (G71 ROUGHING EXAMPLE)
G50 S2000
G96 S200 M03
T0101
G00 X60. Z2.
G71 U2. R1.
G71 P100 Q200 U0.3 W0.2 F0.25
N100 G00 X50.
G01 Z-30. F0.25
X30.
Z-60.
X20.
N200 G00 X60.
G70 P100 Q200
M30
%Explanation:
| Parameter | Description |
|---|---|
| U2. | Depth per pass = 2 mm |
| R1. | Retract = 1 mm between passes |
| P100 / Q200 | Start & end block of contour |
| U0.3 / W0.2 | Finishing allowance (X/Z) |
| F0.25 | Feedrate |
After G71 roughing, G70 uses the same P–Q block to finish the contour.
📌 3. G72 — Facing Cycle (X-axis)
Used for facing operations, removing material along the X-axis (radially).
Format:
G72 W(Depth of Cut) R(Retract)
G72 P(Start) Q(End) U(Finish Allowance X) W(Finish Allowance Z) F(Feed)Example:
G72 W2. R1.
G72 P300 Q400 U0.3 W0.2 F0.2
N300 G00 Z0.
G01 X30. F0.2
Z-10.
N400 G00 Z2.📌 4. G73 — Pattern Repeating Cycle
Used for irregular patterns, grooving, or multi-step diameters with minimal retracts between passes.
Example:
G73 U2. W0.1 R0.5
G73 P500 Q600 U0.2 W0.1 F0.15
N500 G00 X40.
G01 Z-20. X35.
Z-40. X30.
N600 G00 X60.G73 is ideal for small-step roughing and interrupted cuts.
📌 5. G70 — Finishing Cycle
After roughing (G71 or G72), G70 is called to execute the finishing pass using the same profile definition.
Example:
G70 P100 Q200- Executes the exact contour from N100 to N200 at finishing feedrate and allowances.
📌 6. Haas Example — Simplified G71/G70 Workflow
%
O8002 (HAAS TURNING EXAMPLE)
G97 S1200 M03
T101
G00 X60. Z2.
G71 P100 Q200 U2. W0.5 F0.25
N100 G00 X50.
G01 Z-30. X25.
Z-60. X20.
N200 G00 X60.
G70 P100 Q200
M30
%Haas G71 has combined single-line syntax for ease of programming.
📌 7. Siemens Sinumerik Equivalent
CYCLE71(ROUGHING, DEPTH=2, ALLOW_X=0.3, ALLOW_Z=0.2, FEED=0.25)
CYCLE70(FINISHING)Sinumerik uses structured cycles instead of G-code ranges.
📌 8. Heidenhain Equivalent
CYCL DEF 271 TURNING ROUGHING
Q200=+2 ; DEPTH PER CUT
Q201=-60 ; FINAL DEPTH
Q206=0.25 ; FEED
CYCL CALL
CYCL DEF 272 FINISHING
CYCL CALL📌 9. Toolpath Flow Example
- Roughing Pass → G71 removes excess material.
- Finishing Pass → G70 cleans up the contour.
- Facing (Optional) → G72 used for front face cleanup.
- Groove/Recess → G73 for complex patterns.
📌 10. Best Practices
- Always define P–Q contour blocks clearly.
- Include G40 (cancel compensation) before finishing.
- Verify cut depth (U/W) to avoid overcutting.
- Use M08 coolant for chip control.
- Run dry simulation before live execution.
📌 11. Common Mistakes
| Mistake | Result |
|---|---|
| Missing P–Q numbers | Program alarm (cycle undefined) |
| Incorrect retract (R) | Tool gouging or retraction crash |
| Forgetting G70 | Rough part without finish |
| Using wrong plane | Invalid cycle alarm |
📌 12. Advanced Multi-Profile Example
%
O8005 (ADVANCED PROFILE)
G50 S2500
G96 S200 M03
T0202
G00 X60. Z2.
G71 U1.5 R0.8
G71 P500 Q600 U0.3 W0.2 F0.25
N500 G00 X50.
G01 Z-30. X30.
Z-60. X25.
Z-80. X20.
N600 G00 X60.
G70 P500 Q600
M30
%Perfect workflow: roughing → finishing using same contour definition.
📌 13. Future Trends (2025–2030)
- Adaptive roughing cycles — dynamically adjusts pass depth via spindle load.
- AI toolpath optimization — predicts chip evacuation and cutting time.
- Digital twin simulation — real-time G71 path preview inside controller.
✅ Conclusion
CNC turning cycles — G71, G72, G73, and G70 — are essential for efficient, automated roughing and finishing.
By mastering these codes, machinists can dramatically reduce cycle time, improve tool life, and achieve consistent surface quality.
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