GlossaryKind of term: Manufacturing termChatter
What is chatter?
Chatter is a self-sustaining vibration between tool and workpiece during cutting, recognised by a high-pitched noise and a wave pattern on the surface.
Usually the mechanism is regenerative: the waviness left by the previous pass or tooth varies the chip thickness of the next one, and that varying cutting force feeds the vibration. It differs from forced vibration, such as from an imbalance, a worn bearing or the tooth-passing impacts in milling: that follows a fixed spindle or tooth frequency and does not build up on its own. Chatter shows as a high-pitched or droning noise and a regular wave pattern, chatter marks, on the surface.
What does chatter depend on?
Whether a cut chatters depends on the dynamic stiffness of the whole system: spindle, toolholder, tool, workpiece and workholding. A long overhang, a slender cutter, a thin wall or a part sticking far out of the vice lower that stiffness. Depth and width of cut, spindle speed, number of teeth and tool geometry count as well. For a given setup and width of cut there is, at each spindle speed, a depth of cut below which the cut stays stable. That limit follows so-called stability lobes, so a slightly different speed can allow a deeper cut, especially at high spindle speeds. The lobes can be calculated from a measurement of the system's dynamics, for example a tap test.
How does chatter work in practice?
The fix can lie in several places: a shorter or stiffer toolholder, another spindle speed, a smaller depth or width of cut, a cutter with variable pitch, extra support for the workpiece or different workholding. Some of these cost machining time or preparation; another spindle speed sometimes does not. Deep pockets with small corner radii, long slender parts and thin walls often need lower cutting data than an open face, and that belongs in the machining time. Chatter leaves chatter marks, can chip cutting edges and, if it persists, can load the spindle.
What is chatter often confused with?
Chatter is not imbalance: imbalance vibrates at the spindle's rotational frequency, even without cutting, while chatter only occurs during the cut, usually close to a natural frequency of the system. Nor are chatter marks roughness from a blunt tool: a blunt tool gives an evenly rough or torn face, chatter a regular wave pattern.
Frequently asked questions
How do you stop chatter while milling?
By making the system stiffer or changing the cut: shorter overhang, stiffer workholding, smaller depth or width of cut, another spindle speed or a cutter with variable pitch. Which measure works depends on where the weakest link sits.
Why does a thin wall chatter sooner?
Because a thin wall has little stiffness and moves with the cut. Supporting it, bringing the wall to thickness in steps while material still backs it, or lighter cuts help; that can cost extra machining time.
Can you tell from the drawing whether a part will chatter?
Not for certain, but there are signals: deep pockets with small corner radii, long slender parts, thin walls and features that need a long tool overhang. Whether it actually chatters also depends on machine, workholding and tooling.