Turning & Lathes.
Rotational dynamics, tool pressure analysis, and live-tooling synchronization parameters for 2-axis and multi-tasking turning centers.
Constant Surface Speed (CSS)
Unlike milling, where the tool rotates at a fixed diameter, a lathe cuts across a constantly changing diameter as it faces a part. If RPM remains constant, the actual surface footage (SFM) plummets as the tool nears the centerline (X=0). This results in built-up edge and poor surface finish.
Modern CNC lathes utilize G96 (Constant Surface Speed), where the controller dynamically increases the spindle RPM as the X-axis diameter decreases, maintaining a perfect, constant SFM.
The Mathematics of CSS Limit (G50)
Because RPM approaches infinity as diameter approaches zero, a hard limit (G50) must be clamped to prevent the chuck from exceeding its safe mechanical limit and losing grip force due to centrifugal expansion.
Tool Nose Radius Compensation (G41/G42)
Lathe inserts are not perfectly sharp; they have a distinct radius (e.g., 0.015", 0.031"). When programming a chamfer or radius without TNRC, the actual cut will overcut or undercut the geometric profile because the controller assumes the tool is a theoretical sharp point.
| Insert Shape | Included Angle | Typical Application | Relative Strength |
|---|---|---|---|
| C (Rhombic) | 80° | General roughing, heavy turning | Very High |
| W (Trigon) | 80° | Economical roughing (3 edges) | High |
| D (Rhombic) | 55° | Profiling, undercutting | Medium |
| V (Rhombic) | 35° | Deep profiling, finishing | Very Low |
Live Tooling & Y-Axis
The introduction of a Y-axis allows off-center milling operations. Without a Y-axis, "milling" on a lathe (using Polar Coordinate Interpolation - G112) requires synchronized rotation of the C-axis (chuck) and X-axis. While effective, polar milling cannot produce perfectly flat walls on deep features due to the radial nature of the C-axis, making a true physical Y-axis mandatory for tight-tolerance prismatic features.