When trying to understand how tools and workpieces react to vibrations, inducing endmill chatter is a very helpful method. The maker filmed the action on a benchtop CNC router using a specialized high speed camera. The goal was to observe the behavior of the tool and the material when chatter occurs. This project aimed to provide visual data on the subtle movements that define machining stability.
For this test, the maker utilized a mild steel workpiece secured in a milling vise. The machine employed was an AvidCNC Benchtop Pro, and the cutting instrument was a 1/4-inch, 4-flute variable helix carbide end mill from Online Carbide. The footage was analyzed using ImageJ software and frame-difference motion detection. The setup revealed significant motion, showing the workpiece, vice, and spindle and endmill moving around substantially during the chatter phase. One stable cut was filmed at 19,000 FPS using a 0.03-inch width of cut at 24,000 RPM.
The maker observed that the chatter cut resulted in severe oscillations, intermittent chip formation, and tool bouncing, while the stable cut yielded uniform chips without noticeable deflection. Footage confirmed that a too-small width of cut causes skipping and resonance on less rigid routers, confirmed by additional cuts filmed at 20,000 and 11,000 FPS. This points to a theory held by the maker that rubbing, flexing, and resonance occur when the width of cut is too shallow. This was further supported by an aggressive 0.05-inch width of cut which cut cleanly even when the spindle bogged.
Despite the success in visualizing these effects, the final test was not perfect. The brittle carbide end mill fractured cleanly into multiple chunks during the final run. This incident also overloaded the spindle drive, causing the variable-frequency drive to trip even while the axes continued feeding. Moving forward, the maker intends to film HSS tools to see if they demonstrate flexibility compared to the carbide tool used in this build!
Project by Breaking Taps. Watch it on their YouTube channel: