Scallop height is a simple geometric way to estimate the surface texture left by ball-nose tools in 3D milling. It is directly controlled by stepover and tool radius.
When you machine a 3D surface with a ball-nose endmill, each pass of the tool leaves a small cusp or "scallop" between adjacent passes. The height of this scallop is a good approximation of the resulting surface roughness in the toolpath direction.
For a ball-nose tool, a common approximation for scallop height h is:
h ≈ s² / (8 × R)
where:
You can experiment with different values using the CNC Scallop Height Calculator.
Smaller stepovers reduce scallop height and improve surface finish, but they also increase machining time. Larger stepovers are faster, but surface quality suffers. The best choice depends on:
As a rough guideline, finishing operations often use scallop heights in the range of a few microns to a few hundred microns, depending on whether polishing or EDM-relief steps will follow. The exact values are usually defined by internal standards or customer requirements.
Use the geometric formula and calculator to find a good starting point, then validate the result on the machine and adjust based on real surface quality.