Chip thinning: why light cuts need more feed

When radial width of cut drops below half the tool diameter, the real chip gets thinner than your feed per tooth.

Same feed per tooth, two radial engagements. The orange band is the chip thickness the edge actually sees.

At 50% radial engagement or more, the chip thickness matches the programmed feed per tooth. Below 50% the chip gets thinner, and a tool fed at "book" chip load starts rubbing. Harvey Performance gives the adjustment [1]:

RCTF = 1 ÷ √(1 − (1 − 2·WOC/D)²)
Adjusted IPT = IPT × RCTF

Worked example

1/2" tool, 0.05" WOC (10%): 1 − 2×0.1 = 0.8; 0.8² = 0.64; √0.36 = 0.6; RCTF = 1.67. A .002" chip load becomes .0033" programmed.

ChiploadPro shows the factor but does not apply it unless you tick the box, because a higher feed raises the load on a less rigid machine.

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Tooling for this job

Carbide end mills

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Sources

[1] Harvey Performance, Combat Chip Thinning