Stick Slip Friction
Stick-slip is a friction-driven motion instability where a sliding interface cycles between sticking and sudden slipping because static friction exceeds kinetic friction. In CNC machine tools, this causes low-speed feed instability and contouring error as axes near zero velocity build force, break free, and jump forward instead of moving smoothly.
On a CNC shop floor, stick-slip manifests in guideways, table slides, cross-slides, and precision positioning axes during low-speed moves. The saw-tooth motion pattern degrades positioning accuracy and surface finish. For example, a Z-axis may creep unevenly during probing, a lathe carriage hesitate during fine feed, or a milling table chatter during slow contouring, leading to dimensional error and visible waviness. In woodworking and edgebanding, the same instability misregisters panel position and worsens edge alignment. Technically, stick-slip occurs when the friction curve has a negative slope near zero velocity and system compliance releases stored energy suddenly once static friction is exceeded. This directly harms contouring accuracy, positioning accuracy, and surface roughness, requiring proper lubrication, feed rate selection, and servo tuning to mitigate.
Is stick-slip the same as chatter?
No. Stick-slip is a friction-driven low-speed motion instability, while chatter is a dynamic vibration problem from cutting/structure interaction; they can coexist but are different.
What operating region is most vulnerable to stick-slip?
Low-speed motion near zero velocity, especially during start/stop, fine feed, or light-load sliding, is most vulnerable.
What lubricants help reduce stick-slip?
Slideway oils formulated to maintain a stable film and reduce the static-to-kinetic friction gap, with tackifier packages for vertical or inclined ways, are effective.