Chatter is the loud, patterned vibration that leaves a rippled finish and chips tools. It’s a feedback loop: a small vibration leaves a wavy surface, the next tooth hits that wave and vibrates more. Breaking the loop means changing rigidity, speed, or engagement.
Fixes, roughly in order of impact
- Increase rigidity — the single biggest fix. Reduce tool stickout, choke up in the holder, support the workpiece, tighten everything.
- Change spindle speed — every setup has “sweet spot” RPMs; nudging speed up or down often kills chatter instantly.
- Adjust depth/width of cut — sometimes a deeper cut is more stable than a shallow one; experiment both ways.
- Use a sharp tool — dull edges rub and excite vibration.
- Climb mill — it often runs more smoothly than conventional.
Frequently asked questions
What causes chatter? A vibration feedback loop, usually from too much stickout or a bad speed/engagement combination.
Fastest fix? Reduce tool stickout and try a different spindle speed.
Does climb milling help? Often yes — it tends to run more smoothly.
If nothing else works, a small change in axial depth or a tool with unequal flute spacing (a “variable-helix” end mill) can disrupt the vibration that causes chatter. These tools are designed specifically to break the resonance feedback loop.