Chip Thinning Calculator
Running less than 50% radial engagement? Your actual chip is thinner than your programmed chip load — this tells you how much to bump feed to compensate.
Why a thin stepover thins the chip
At full radial engagement, each flute sweeps through the maximum possible chip thickness for its programmed feed per tooth. Drop the radial depth of cut well below the tool radius, and the flute only engages the material for a short arc near the point of maximum thickness — the average chip over that shorter engagement ends up meaningfully thinner than the programmed chip load, even though nothing about the feed rate setting changed.
The formula
Chip thinning factor = 1 ÷ (2√((RDOC/D) × (1 − RDOC/D))), valid for radial engagement up to 50% of the tool diameter. Multiply your programmed chip load by this factor to get the feed you should actually run to restore the chip thickness the tool is designed to cut — at exactly 50% engagement the factor is 1 (no adjustment needed), and it grows quickly as radial engagement drops below that.
Above 50% engagement, skip this calculator
Once radial engagement passes 50% of the tool diameter, chip thinning stops applying and the programmed chip load is already close to the actual chip thickness — this calculator is specifically for light stepovers common in HSM (high speed machining) toolpaths, adaptive clearing, and finishing passes, not for slotting or heavy conventional roughing.