FANUC Smooth TCP and tool posture: why a correct tool-tip path still requires orientation checks in side milling
Official FANUC 30i/31i-A5 material distinguishes TCP, Tool Posture Control and Smooth TCP. Geometry of a reference point on the tool axis shows how angular differences grow with distance, without equating the tool-tip path with the path of the entire tool.
Contents
In five-axis verification, a tool-tip trajectory close to the target curve does not establish that positions farther along the tool also move as intended. Where side milling involves an extended contact region, changing tool orientation is another quantity that must be checked.
What the three function names address
FANUC's official 5-Axis Machining brochure, MBA-025-EN_03_1308, 2013 edition, PDF pages 2 and 7 uses 30i and 31i-A5 as its context. TCP keeps the controlled tool-tip point on the programmed path; Tool Posture Control extends control to the orientation trajectory, mainly for side milling. Smooth TCP smooths abrupt CAM-generated orientation changes and rotary-axis motion; High-Speed Smooth TCP also optimizes side-milling motion under posture control. The brochure does not specify configuration requirements for every software version. This article does not assume that these functions are present on every five-axis machine.
Use a point on the tool axis to isolate the angular effect
The following is an original ideal rigid-body model. The tool tip T is fixed, and unit vector u gives the tool-axis direction from tip toward holder. A reference point at distance h along the axis is P=T+hu. It is an axis point or cross-section center, not an actual side-contact point; the latter also depends on tool radius, contact side and workpiece surface.
If the angle between two orientations is δ, the distance between the reference points is the chord of an isosceles triangle: |ΔP|=h|u₂−u₁|=2h sin(δ/2). For the original example δ=0.1°:
| Distance h from the tool tip | Position difference of the axis reference point |
|---|---|
| 20 mm | About 0.03491 mm |
| 80 mm | About 0.13963 mm |
| 160 mm | About 0.27925 mm |
In all three cases the tool-tip position difference can be zero. The farther the reference point, the larger the displacement associated with the same angular difference. These values are geometric differences between two orientations, not manufacturer accuracy specifications or predicted overcut depths. Actual surface error cannot be read directly from the table.
Why verification files must retain orientation data
Saving only the XYZ tool-tip path is equivalent to saving T alone; it cannot reconstruct u in P=T+hu. Compare tool-tip position and tool direction from two postprocessor outputs in the same coordinate representation, distinguishing intentional continuous tilting from unreasonable direction jumps between blocks. Even with the same tool-tip path, changing orientation data can change the space swept by the tool.
Rotary-axis angles also depend on machine kinematics. Subtracting A, B and C values directly between two different machine structures does not yield tool-orientation difference. First obtain each tool-direction vector, then perform the geometric comparison above.
Smoothing and surface acceptance require different checks
Smoothing functions address changes in motion. Whether a particular side-milling operation meets contour requirements still requires checking tool geometry, the contact region and the complete swept volume. This article supplies no enable command, tolerance parameter or performance guarantee. It offers a geometric method for understanding why a correct tool tip is insufficient. Other five-axis resources are in the OPTION section.