In G-code, G94 signifies that the programmed feed rate (F-value) should be interpreted as feed per minute. This means the cutting tool will advance a specified distance over a minute's time, irrespective of the spindle's rotational speed.
Understanding G94 Feed Mode
G94 is a fundamental G-code command in CNC programming, primarily used to establish how the machine interprets the feed rate (F-value) for cutting operations. When G94 is active, the numerical value following the 'F' in a program block represents a linear speed, such as inches per minute (IPM) or millimeters per minute (MMPM).
This feed mode is particularly common and often the default for:
- Milling machines: For general milling, drilling, reaming, and tapping operations where a consistent linear feed is desired.
- Turning centers: For specific operations where controlling the linear movement rate is more critical than linking it directly to spindle revolutions.
G94 vs. G95: Key Differences
While G94 sets the feed rate in units per minute, another common feed mode, G95, specifies the feed rate in units per revolution. Understanding the distinction is crucial for effective CNC programming.
Here’s a comparison:
| Code | Application | Description |
|---|---|---|
| G94 | Per minute feed (M, T) | The tool travels a specified distance per minute (e.g., IPM, MMPM), regardless of spindle speed. Ideal for milling, drilling. |
| G95 | Per revolution feed (M, T) | The tool travels a specified distance per spindle revolution (e.g., inches per revolution, mm per revolution). Often used in turning or for operations like threading. |
| G96 | Constant surface speed control (T) | Maintains a constant cutting speed at the tool tip by adjusting spindle RPM. Primarily for turning. |
| G97 | Stop constant surface speed control (T) | Deactivates G96 and reverts to a constant RPM. Primarily for turning. |
(M = Machining Centers, T = Turning)
Practical Applications of G94
G94 is typically the preferred feed mode for most milling operations because it allows for direct control over how fast the tool moves through the material.
- Drilling: When drilling a hole, a specific feed rate in IPM/MMPM ensures consistent chip evacuation and prevents tool breakage, irrespective of the material or tool diameter which might influence optimal spindle speed.
- Milling: For general contouring or pocketing, G94 provides a straightforward way to manage material removal rates. Programmers can easily adjust the feed to optimize surface finish or cycle time.
- Tapping: Although sometimes combined with G95 for synchronized tapping, G94 can also be used, requiring precise coordination between spindle speed and feed rate.
To activate G94 in a G-code program, you simply include it in a block. For example:
G00 G90 G20 G17 ; Initial setup
G94 ; Set feed rate to inches per minute
S1500 M03 ; Spindle on, 1500 RPM
G01 X1.0 Y1.0 F10.0 ; Move to X1.0 Y1.0 at 10 inches per minuteFor more details on G-codes and their applications, you can refer to resources like G Codes for Machining Centers - Carbide Depot.
