Introduction to CNC Canned Cycles
When starting out with CNC programming, the numerous canned cycles can seem quite overwhelming. These cycles are fundamental for automating common machining operations, but distinguishing their specific functions requires some clarity. A prevalent question among beginners is: What is the actual difference between G73 and G83?
In essence, G73 is a peck drilling cycle designed for shallow holes with short retracts, while G83 is intended for deep hole drilling with full retraction to facilitate chip evacuation.
Often, G73 is described as “break chip drilling,” and G83 as “deep hole drilling.” The primary goal of G73 is to prevent long, stringy chips from wrapping around the tool, whereas G83 aims to efficiently clear chips from deep bores by retracting completely after each peck.
Table of Contents
- G73 Peck Drilling
- G83 Deep Hole Drilling
- When to Use G73
- When to Use G83
- Optimizing Q Values for Efficiency
- Techniques to Accelerate Cycle Times
- Situations to Avoid Pecking
G73 Peck Drilling Explained
G73 is predominantly utilized to break up long and continuous chips during drilling operations. When chips become excessively lengthy, they pose safety hazards, risk damaging the workpiece, or can cause machine malfunctions. Chips that wrap around the spindle or clog chip conveyors can lead to dangerous situations or machine downtime.
To illustrate, consider the standard drilling cycle G81:
G81 X1.0 Y1.0 Z-0.25 R0.1 F2.5; X2.0; X3.0; G80;
This cycle moves the tool to specified XY coordinates, drills to the Z depth, and then retracts to the R-plane. Repeating this cycle at different positions allows multiple holes to be drilled efficiently. However, the chips produced are continuous and can cause issues.
G73 enhances this process by introducing a series of small retractions, known as pecks, typically around 0.010″ to 0.020″. This intermittently breaks the chips into shorter segments, reducing the risk of entanglement or damage. The key parameter, Q, controls the depth of each peck:
G73 X1.0 Y1.0 Z-0.25 R0.1 F2.5 Q0.1; X2.0; X3.0; G80;
> Here, instead of drilling continuously to Z-0.25, the tool advances in incremental steps, breaking the long chips into manageable pieces. This method not only promotes safer operations but also maintains high cycle speeds, making G73 a preferred choice for shallow drilling where chip control is critical.
G83 Deep Hole Drilling: An Overview
G83 differs significantly from G73. Its primary purpose is to facilitate the drilling of deep holes by ensuring effective chip removal and cooling. Deep holes present unique challenges: coolant often struggles to reach the tip of the drill, chips have difficulty evacuating, and the drill can overheat or break due to trapped chips and inadequate cooling.
The hallmark of G83 is its full retraction after each peck, returning the tool to the R-plane or original Z position. This ensures that chips are completely cleared from the hole, and coolant can reach the cutting edge, thus preventing excessive heat buildup and reducing tool wear.
When Should You Use G73?
If your drilling involves shallow holes where chips do not tend to become excessively long, a standard G81 cycle is sufficient. Typically, for holes with a depth less than or equal to the diameter (1×D), G81 or G73 is suitable. When chips start to get longer or if there’s a risk of entanglement, implementing G73 with pecking can help maintain smooth operations and safety.
When is G83 Preferable?
For holes where the depth exceeds four times the diameter (4×D) or more, G83 becomes essential. Its full retraction cycle ensures chips are evacuated effectively, and coolant reaches the drill tip. For example, with a 0.25″ diameter drill, G83 should be used for holes deeper than approximately 1″. Depending on the material and particular machining conditions, even shallower holes might benefit from G83’s advantages.
Setting Optimal Q Values
The Q parameter determines the depth of each peck in G73 cycles. Fine-tuning Q is crucial for balancing cycle time and chip control. Larger Q values (up to 1×D) reduce the number of pecks, speeding up drilling but risking longer chips. Conversely, smaller Q values generate shorter, safer chips at the expense of longer cycle times.
For most applications, a Q of 0.100″ to 0.150″ for drills in the 0.250″ to 0.500″ range is effective. For smaller tools, a Q of 0.050″ might be more appropriate. Adjust Q based on material, chip breaking characteristics, and machining priorities.
Strategies to Accelerate Cycle Times
Some CNC controllers support variable peck depths, allowing the initial peck to be deeper and subsequent pecks to be shorter. This approach minimizes unnecessary retracts and reduces overall cycle time. For example, using a three-step peck: first peck at 3×D depth, second at 2×D, and subsequent pecks at 1×D can significantly improve efficiency.
On machines like Haas, programming I, J, and K parameters enables this variable pecking. For instance, in a G83 cycle:
G83 X1.0 Y1.0 Z-2.0 R0.1 F2.5 I0.75 J0.25 K0.25;
> I specifies the initial peck depth, J defines the decrement for subsequent pecks, and K sets the minimum peck depth. This technique is especially advantageous in high-volume production, where saving seconds per hole translates into substantial time savings.
When to Avoid Pecking
While pecking is beneficial in many scenarios, there are situations where it is best avoided. For instance, when drilling shallow holes, pecking adds unnecessary cycle time. Additionally, avoid pecking with certain tools or conditions:
- Using carbide drills with high-pressure through coolant systems, where continuous drilling is more effective.
- Tools with built-in chipbreakers designed to eject chips without pecking.
- Specialized drills like U-drills, which rely on their geometry and coolant to break chips efficiently.
- Solid carbide drills, which can chip or fracture under repeated pecking motions.
Understanding these distinctions helps optimize machining efficiency and tool longevity, leading to safer and more effective operations.