What is this cyclical sound I’m hearing?

Cyclical sounds result from some sort of regular, repeating event involving our cutting tool or machine. The frequency of the sound often matches the speed of the spindle (once per revolution) or the natural frequency of something in our machining set up. Some of the most common cyclical sounds occur due to chatter, interrupted cuts, or dull cutting tools.

Chatter is a screeching or singing sound that occurs when a machine or workpiece hits its resonant frequency.

Interrupted cuts occur when the tool is not in constant contact with the workpiece. The repeated impact of the tool on the workpiece creates a repetitive sound. To hear different examples of interrupted cuts (non constant contact between the tool and the workpiece), listen here.

Dull blades may have missing, bent, or dull cutting edges/teeth. This makes a sound each time the dull portion passes through the workpiece. For an example of a dull saw blade, listen here. For more on mill sounds, click here.