Understanding Stability Lobe Diagrams

​We have explained how every tool/toolholder/spindle/machine combination has a stability lobe diagram and they are all different. The lower axis is spindle speed and the right axis is depth of cut. The white areas are stable and the red areas are unstable where the tool will likely chatter. The region in blue is called the "b-Limit or Unlimited Speed" range. The cutting force is low enough not to cause the tool to deflect. If the diagram is set to a full slot then any axial depth of cut under the b-limit will be stable at any speed. Used with high feed mills. If the diagram is set to the full cutting length of the tool then any radial engagement or step-over under the b-limit will be stable at any speed. Exploitable by Trochoidal HSM milling. The yellow area is the "Process Damped" region. The tool is rotating slow enough that the vibration one tooth is dissipated before the next tooth comes through. You can cut as deep as you want in this region. Variable Pitch Endmills can increase this region speed significantly. The following closer pitch tooth acts as a damper for the previous tooth. 

The b-limit is determined by the stiffness of the tool assembly. The Process Damping Wavelength can be determined experimentally.