Why does my CNC router chatter, and how do I actually fix it?

Chatter is a self-reinforcing vibration between the cutter, workpiece, spindle, and machine structure; it leaves ripples, noise, poor finish, and shortened…

Chatter is a self-reinforcing vibration between the cutter, workpiece, spindle, and machine structure; it leaves ripples, noise, poor finish, and shortened tool life. Start with rigidity: clamp the stock firmly, shorten cutter stick-out, check collet and bearings, and use the largest practical tool diameter. Then change one cutting variable at a time—spindle speed, feed, radial engagement, or depth—because a different RPM can move the cut into a stable zone rather than simply making everything slower.

Why chatter is a vibration problem, not a sharpness problem

Chatter is the tool, workpiece, and machine falling into a self-excited vibration — each pass of the cutter leaves a wavy surface, and the next pass hits those waves and bounces harder. That is why a brand-new bit can chatter as badly as a dull one, and why the fix is usually about stiffness and rhythm, not buying sharper tools.

What to do, step by step

1. Shorten the tool stick-out. Every extra bit of exposed tool multiplies flex; seat the bit as deep as the collet safely allows.
2. Change spindle speed in real steps — 10-15% up or down — to move out of the resonant zone, rather than creeping 100 RPM at a time.
3. Reduce depth per pass and increase feed slightly. A tool that is cutting, not rubbing, vibrates less.