G93, G94, and G95 are the three fundamental CNC feedrate modes that determine how the machine interprets F commands. Understanding these modes is essential for accurate machining, especially in high-speed 3D surfacing, turning operations, multi-axis toolpaths, and synchronized spindle motion. Improper feed mode selection can result in tool breakage, poor surface finish, incorrect chip load, and unpredictable axis behavior. Mastering these feed modes is a key skill for any professional CNC programmer in 2025.
1. G94 – Feed Per Minute (Most Common)
G94 sets the feedrate in units per minute (mm/min or inch/min).
F1000 means the tool moves at 1000 units per minute.
Used for:
- 3-axis milling
- Drilling
- Tapping with feed-per-minute cycles
- General contouring
Example:
G94
F2500
G01 X80. Y20. Z-8.
This is the default for nearly all milling applications.
2. G95 – Feed Per Revolution (Turning + Synchronized Milling)
G95 links the feedrate to the spindle speed.
F0.25 means the tool moves 0.25 units per spindle revolution.
Used for:
- CNC turning
- Threading
- Groove cutting
- Heavy roughing where chip load must remain constant
- Live-tool milling requiring synchronized feed
Example:
G95
S800
F0.20
G01 X42. Z-16.
Feed automatically adjusts if spindle speed changes.
3. G93 – Inverse Time Feedrate (Required in 5-Axis Machining)
G93 is the most misunderstood feed mode.
It changes feedrate to “time to complete the move.”
F value becomes the inverse of seconds.
Example:
F0.015 → move completes in 1 / 0.015 = 66.66 seconds
F0.5 → move completes in 2 seconds
Used for:
- Simultaneous 5-axis machining
- Complex surface finishing
- Post-processors for multi-axis CAM
- High-precision rotary toolpaths
Example:
G93
G01 X50. Y30. Z-12. A35. C110. F0.0125
This tells the machine to execute the move in exactly 80 seconds.
4. Real 5-Axis Example (Why G93 Is Critical)
Without G93:
A 5-axis toolpath may accelerate unpredictably → chatter marks.
With G93:
Feedrate is time-based → smooth and consistent motion.
Typical CAM post output:
G93
G01 X55. Y40. Z-5. A22. C45. F0.0102
G01 X58. Y43. Z-5.2 A23. C46. F0.0098
Each line explicitly defines the duration of the move.
5. Common Mistakes to Avoid
Mistake 1 — Forgetting to turn off G93
Result: Z-rapid moves become extremely slow or extremely fast.
Always end with:
G94
Mistake 2 — Wrong feed mode in turning
Using G94 in threading leads to broken tools.
Mistake 3 — Setting the wrong F value in G93
Inverse time feeds are small decimals, not large numbers.
Mistake 4 — CAM posts mixing G93 and G94 incorrectly
Always check start/end blocks.
6. Practical Summary
- G94: Feed per minute → milling standard
- G95: Feed per revolution → turning + synchronized moves
- G93: Inverse time feed → simultaneous 5-axis
Mastering these modes guarantees correct chip load, better surface finish, safer machining, and more consistent high-speed performance. For 2025 and beyond, with multi-axis machining on the rise, understanding G93/G94/G95 is mandatory for professional CNC programmers.
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