G70 is the dedicated finishing cycle for Fanuc and Fanuc-compatible CNC lathes. It takes a previously roughed profile—usually generated by G71 (rough turning), G72 (facing), or G75 (groove pecking)—and executes a clean, precise finishing pass using the same profile definition. G70 guarantees dimensional accuracy, improved surface finish, and perfect geometric consistency regardless of how aggressive the roughing passes were. It is one of the most important cycles in professional turning because it decouples roughing and finishing operations for maximum control.
1. What G70 Actually Does
G70 reads the same profile block defined by G71/G72:
- P → start block
- Q → end block
Then it executes:
- A smooth contour pass
- Using the active tool
- At finishing feedrates and cutting parameters
- Using finishing allowances defined during roughing
This ensures the final geometry is accurate and stable.
2. Basic Syntax (Modern Fanuc)
G70 P(start) Q(end)
Example:
G70 P100 Q200
This finishes the profile defined between N100 and N200.
3. Typical Workflow (Industry Standard)
- G71 rough turn profile
- G70 finish the same profile
Example:
G71 U2.0 R0.5
G71 P100 Q200 U0.3 W0.1 F0.25
G70 P100 Q200
This is the most common sequence in the world of CNC turning.
4. Real External Turning Example
Profile:
N100 G00 X60. Z2.
N110 G01 Z-45.
N120 G01 X30.
N200
Roughing:
G71 U2.0 R0.5
G71 P100 Q200 U0.3 W0.1 F0.30
Finishing:
G70 P100 Q200
This produces a clean, accurate OD profile.
5. Internal Boring Finishing Example
N300 G00 X40. Z2.
N310 G01 Z-35.
N320 G01 X60.
N400
G71 U1.5 R0.3
G71 P300 Q400 U0.25 W0.10 F0.22
G70 P300 Q400
Perfect for precision internal bores.
6. Finishing After G72 Facing Cycle
G72 W1.8 R0.4
G72 P500 Q600 U0.3 W0.1 F0.25
G70 P500 Q600
Produces a perfect faced surface.
7. Finishing After G75 Groove Cycle
G75 R0.2
G75 X42. Z-10. P2500 Q200 F0.18
G70 P700 Q800
Ensures exact groove width, depth, and sidewall finish.
8. Important Requirements for G70 to Work Correctly
- The profile between P and Q must be continuous
- There must be no axis reversal issues
- The finishing insert must be aligned to the profile
- Cutting parameters must be appropriate for finishing
9. Common Mistakes & Fixes
Problem: Machine alarms “profile undefined.”
– Missing N number labels
– Wrong P/Q values
Problem: Finish cuts air or skips areas
– Roughing left zero allowance
Fix: Increase U/W in G71/G72
Problem: Poor surface finish
– Reduce feedrate
– Increase spindle speed
– Use a wiper insert
Problem: Wrong tool for finishing
– Finishing should use a sharp, high-positive insert
– Tool nose radius must match part’s geometry
10. Pro Finishing Tips for 2025 Standards
- Always finish using G96 CSS mode
- Use wiper inserts for mirror-quality surfaces
- Leave 0.15–0.30 mm stock in roughing for steel
- Leave 0.05–0.10 mm for aluminum
- Use coolant at high pressure during deep finishing
- Add chamfers and radii explicitly inside profile blocks
Example:
N110 G01 Z-40.
N120 G03 X32. Z-45. R5.
11. Summary
G70 is an essential finishing cycle that ensures perfect geometry after roughing. It delivers top-level dimensional accuracy, excellent surface finish, and highly repeatable results. Whether used after G71, G72, or G75, G70 is the final step that defines true machining quality in modern 2025 CNC turning environments.
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