G73 Canned Cycle Motion: An In-Depth Look
The G73 command is primarily designed to facilitate fast, efficient peck drilling by breaking up long, continuous chips during the drilling process. This cycle is especially useful when working with jobber drills or counterboring tools, where long, stringy chips can cause significant operational issues. As the drill advances into the workpiece, the machine rapidly retracts slightly—typically by about .010 to .020 inches—to fracture the chips before resuming cutting. This quick retraction minimizes cycle time while preventing chip accumulation that could jam the tool or interfere with coolant flow.
Visual demonstrations of this motion highlight how G73 effectively mitigates chip entanglement, unlike standard G81 drilling cycles which can produce long, problematic chips. Implementing G73 ensures cleaner machining processes, reduces downtime, and improves overall workpiece quality by maintaining optimal chip control and coolant access.
G73 Command Structure and Parameters
The G73 cycle utilizes several key parameters that define its operation:
- X: Specifies the X-axis coordinate of the hole center.
- Y: Specifies the Y-axis coordinate of the hole center.
- Z: Defines the final hole depth relative to the program’s origin, used in absolute positioning.
- R: Sets the retract plane—where the tool will rapidly lift to before advancing to the final depth. In G98 mode, the tool retracts to the initial Z position; in G99 mode, it retracts to this R plane.
- Q: Determines the peck depth—the incremental depth the tool cuts before retracting to break the chips.
- P: An optional dwell time at the cycle’s end, measured in milliseconds, with 1000 equaling 1 second.
- F: The feed rate during cutting, usually specified in inches per minute when in G95 mode.
Sample Program Demonstrating G73 Usage
Suppose you’re machining a 6061 aluminum block with a 1/4″ high-speed steel jobber drill, targeting shallow holes 1″ deep. After completing facing, profiling, and spotting, you focus solely on drilling. G73 becomes ideal here to prevent long chip formation and potential jams.
Here is an example program for drilling multiple holes:
O1000
( BLOCK_DRILLING )
G00 G17 G40 G90 G20
N10 ( OPERATION: DRILLING )
T01 M06 ( Select 1/4" HSS Jobber Drill )
G00 G54 X1.2 Y-1. S4000 M03 ( Position above first hole, spindle on at 4000 RPM )
G43 Z.125 H01 ( Apply tool length offset, move 0.125" above workpiece )
M08 ( Coolant ON )
G73 Z-1.0 R0.1 F16 Q0.0625 ( Drill to depth with pecking, retract at 0.1" )
X2.4 ( Move to second hole X position )
X3.6 ( Move to third hole X position )
X4.8 ( Move to fourth hole X position )
G80 ( Cancel canned cycle )
G00 G91 G28 Z0.0 ( Retract Z axis to machine home )
G00 G91 G28 Y0.0 ( Retract Y axis to home for inspection )
G90 ( Return to absolute positioning mode )
M30 ( End of program )How to Determine Appropriate Peck Depth (Q)
Selecting the right Q value is relatively straightforward compared to cycles like G83, as pecking occurs rapidly with minimal impact on total cycle time. The key factors influencing Q include material type and chip length. Softer or gummy materials that tend to produce nests require smaller Q values to avoid tangled chips. A good starting point is to set Q at approximately one-quarter of the drill diameter. For instance, a 1/4″ drill suggests a Q of about 0.0625, resulting in manageable, short chips that are less likely to cause issues. When running your program, observe the chip formation. If chips are less than 4 inches long and don’t wrap around the tool, you’ve optimized your parameters effectively.
Critical Considerations and Troubleshooting
The actual retract distance during the cycle is governed by machine parameters, typically set between .010″ and .020″. Modern machines generally perform well with a .010″ retract—assuming the ballscrews are in good condition and the machine is responsive. Worn-out or older machines might require a slightly larger retract to ensure effective chip breaking. If chips are not breaking as desired, consider increasing this parameter accordingly. Refer to your machine’s manual for the specific setting.
Note that certain materials like cast iron or brass naturally produce short, brittle chips, often eliminating the need for a chip-breaking cycle. Ultimately, fine-tuning the cycle parameters through experimentation will yield the best results tailored to your specific application and tooling. Remember, practical observation and incremental adjustments are key to optimal performance.