AiVibeStability Lobe Diagram
A stability lobe diagram plots the limiting depth of cut against spindle speed, showing which combinations are expected to cut stably and which are expected to chatter, based on regenerative chatter theory.
The diagram is calculated from the frequency response function of the tool, holder and spindle, measured at the tool tip by impact testing with an instrumented hammer and accelerometer, together with cutting force coefficients for the workpiece material and tool. Plotting the stability limit across spindle speeds produces a series of lobes. Below the lobe boundary the cut is predicted to be stable; above it, chatter is expected.
Machinists and process engineers use the diagram to pick spindle speeds that fall in the pockets between lobes, where much deeper cuts are stable than at neighbouring speeds. The benefit is largest at higher speeds, where tooth-passing frequency approaches the dominant natural frequency of the tool assembly and the lobes are widest, which is why the method is popular in high-speed aluminium machining.
The prediction is only as good as the measured dynamics, and those change with tool length, holder, clamping, wear, spindle speed and temperature. Workpiece flexibility, as in thin walls, adds dynamics not captured by a tool-tip measurement. Diagrams should therefore be confirmed with test cuts, and remeasured when the tool assembly changes.
Key points
- Plots limiting depth of cut against spindle speed
- Calculated from tool-tip frequency response and cutting coefficients
- Stable pockets between lobes allow deeper cuts at selected speeds
- Needs remeasurement when tool length, holder or clamping changes
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory: edge devices plus AI agents that let people talk to CNC, PLC and robot controllers in plain language. Agents only propose changes, and a trained operator confirms each one.