**1. Tool Location**
The tool location is a reference point on the cutting tool. The path that this point follows during machining is known as the tool path or programmed path. It serves as the basis for all movement commands in CNC programming.
**2. Tool Setting and Setup**
Tool setting involves positioning the tool’s reference point relative to the machine coordinate system using precise measuring methods before running the NC program. This step is crucial, as it directly affects the accuracy of the machined part. Common tools used for tool setting include dial indicators, feeler gauges, and gauge blocks. In some cases, a coordinate probe may also be used. Proper setup ensures that the tool’s position is accurately defined, which is especially important in batch production where repeatable accuracy is essential. Operators should develop a strong understanding of their CNC equipment and master various tool-setting techniques to ensure consistent results.
**3. Selection Principles for Tool Points**
A good tool point should be easy to locate, measure, and calculate during programming. It should have a clear relationship with the part’s positioning reference. For example, it could be a point on the part itself (such as the center of a hole) or an external reference like a fixture. The selected point must allow for high precision, even if the part’s overall tolerance is not tight. Additionally, the tool point should be on a stable and accessible surface to minimize errors during machining. Ideally, it should align with the design or process reference to avoid complications from coordinate conversions and simplify the NC program.
**4. Tool Point Selection Methods**
For CNC lathes or milling machines, the X and Y axes are typically set by the machine, so only the Z-axis needs to be defined as the tool point. On three-axis milling machines, both the origin (X0, Y0, Z0) and the workpiece coordinate system (like G54–G57) must be established. The tool point can be on the part or the fixture, but it must relate to the part’s reference. For four- or five-axis machines, additional rotation axes (A, B, C) are involved, requiring more complex setups. However, modern CNC systems often provide multiple tool-setting options, making the process more flexible.
**5. Zero Drift**
Zero drift refers to a gradual loss of accuracy in CNC machining due to environmental factors such as temperature, coolant, tool wear, and changes in spindle speed or feed rate. Even under identical conditions, repeated machining may result in slight variations in part dimensions. This phenomenon is common in CNC operations and can affect the machine’s performance if left unchecked. Regular calibration and monitoring help mitigate its impact.
**6. Tool Compensation**
As tools wear over time, their dimensions change, affecting machining accuracy. To compensate, CNC systems use tool length compensation and tool radius compensation. These adjustments ensure that the actual tool path remains aligned with the programmed path, maintaining dimensional accuracy throughout the machining process.
**7. Tool Radius Compensation**
During contour machining, the tool’s radius must be considered to ensure the final shape matches the design. The tool’s center path differs from the actual part geometry, so a radius offset is applied. This is known as tool radius compensation. UG/CAM software programs the ideal tool path based on an assumed perfect tool, so real-world tool wear must be accounted for through compensation to maintain quality.
**8. Tool Length Compensation**
When tools are worn or replaced, their tip position may no longer match the original programmed location. Tool length compensation adjusts the offset value to ensure that the depth of cut or surface position remains accurate. This is critical in milling and drilling operations to meet design specifications.
**9. Machine Coordinate System**
The machine coordinate system is based on the Cartesian coordinate system, with X, Y, and Z axes defining linear motion. Rotational axes (A, B, C) correspond to rotations around X, Y, and Z, respectively. The Z-axis typically aligns with the tool’s axis, while X and Y are perpendicular to it. The right-hand rule defines the positive direction of each axis. This system serves as the foundation for all machining operations.
**10. Workpiece Coordinate System and Origin**
The workpiece coordinate system, also called the programming coordinate system, is established by the programmer with a specific point on the part as the origin. This origin, referred to as the part zero or program zero, is used to define tool paths. The offset between the workpiece origin and the machine origin is stored in the CNC system and automatically applied during machining. Multiple workpiece coordinate systems (e.g., G54–G59) can be set, allowing flexibility in programming and setup.
**11. Clamping Origin**
In machines with swiveling tables, such as rotary centers, the clamping origin is used to define the reference point for workholding. This origin is stored in the CNC system and used for offset calculations, ensuring consistent positioning across different setups.
Overall, proper tool setup, accurate coordinate systems, and effective compensation strategies are essential for achieving high-quality CNC machining. Understanding these concepts helps operators optimize efficiency and maintain precision throughout the manufacturing process.
Nantong Ecotherm Insulations Co., Ltd , https://www.vactherm-insulation.com