Welcome to our simple guide on the G78 CNC code. Whether you are new to CNC programming or an experienced machinist, understanding the G78 code is essential.
This guide will explain everything you need to know about this unit mode command—what it is, when to use it, and why it matters.
(Step-by-step.)
Key Takeaways
- The G78 threading cycle is a Fanuc control CNC command used for internal, external, taper, and multi-start threading operations.
- The G78 command has a double-block format, defining thread parameters and end values in the x-axis and z-axis.
- The P parameter controls thread behavior, including the number of spring passes, thread run out, and flank angle or infeed angle.
- The G78 command format consists of G78, P, Q, R, and F, where F defines the thread pitch and Q is the depth of cut.
- The G78 threading cycle is similar to the G76 threading cycle, with the same thread calculations and parameters, but with a different command placement.
G78 Threading Cycle Overview
Operating a CNC machine with a Fanuc control system often requires executing specific threading cycles to produce precise threads.
The G78 threading cycle is a Fanuc control CNC command used for threading operations, analogous to the G76 threading cycle. You’ll use the G78 command in some Fanuc control CNC models, with the main program remaining the same as G76, but with a different command placement.
This cycle can be used for internal, external, taper, and multi-start threading operations, with variations in the command format and parameters. The G78 threading cycle has a double-block format, defining thread parameters and end values in the x-axis and z-axis.
It behaves in a parallel manner to the G76 threading cycle, with the same thread calculations and parameters.
Threading Cycle Command Parameters
When executing a G78 threading cycle, you’ll need to specify several command parameters to control the threading operation.
These parameters, specific to Fanuc control, define the threading process and its outcome. The P parameter, for instance, consists of multiple values controlling thread behavior, including the number of spring passes, thread run out, and flank angle or infeed angle.
The Q parameter defines the depth of cut, determining the amount of material removed in each pass. The R parameter specifies the depth of the finish cut, the final cut taken to achieve the desired thread dimensions.
Additionally, the F parameter defines the thread pitch, while the X and Z parameters define the end values in the x-axis and z-axis, respectively.
G78 Code Format Breakdown
You’ve specified the command parameters for the G78 threading cycle, now it’s time to break down the code format.
The G78 threading cycle format consists of G78, P, Q, R, and F. G78 is the G code for the threading cycle, P consists of multiple values controlling thread behavior, Q is the depth of cut, R is the depth of finish cut, and F is the thread pitch.
In Fanuc control, the code format is divided into two blocks. The first block includes P and Q, where P controls thread behavior, and Q determines the depth of cut.
The second block includes X, Z, P, Q, and F, specifying the thread depth, depth of the first cut, and thread pitch.
CNC Machine Threading Operations
In CNC machining, threading operations require precision and control to produce accurate threads.
When using the G78 threading cycle on a Fanuc control CNC model, you’ll need to input specific values to achieve the desired thread characteristics. The G78 command includes parameters such as the number of finished paths, chamfer amount, angle of tool tip, each cut, finishing allowance, minor diameter, and thread pitch.
These values are vital for creating threads with precise thread depth, calculated as Pitch x 0.61363. With the G78 threading cycle, you can control the thread behavior, including the number of spring passes, thread run out, and flank angle.
Set the spindle speed and rapid action commands, such as N30 G00 X45 Z5, to move quickly to specific locations and position the tool for threading operations.
Thread Calculations and Examples
Now that you’ve input the necessary parameters for the G78 threading cycle, it’s time to calculate the thread dimensions.
To guarantee precise results, you’ll need to ponder factors like threading depth, pitch, and diameter.
- Threading depth: Calculate the depth of the thread by subtracting the minor diameter from the major diameter.
- Pitch: Determine the thread pitch in mm by dividing the threading length by the number of threads.
- Spindle speed: Calculate the spindle speed based on the threading pitch and the desired cutting speed.
- Finish cut: Calculate the finish cut depth to verify a precise thread profile.
With these calculations complete, you can confidently execute the G78 threading cycle on your Fanuc control CNC machine, using the tool tip to precision-cut the thread.
CNC Codes Similar to G78
|
Code
|
Mode
|
|---|---|
| G76 | Automatic threading cycle (canned cycle) |
| G92 | set an offset in all coordinate systems |
| G32 | Threading cycle for straight and tapered threads |
| G33 | Thread cutting, constant lead |
| G34 | Variable lead threading |
| G77 | Outer/Internal diameter drilling |
| G79 | Face cutting cycle |
| G24 | Cutting cycle B |
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