Glossary & Reference
Radial depth of cut — ae — is how much of the cutter's diameter is actually engaged sideways in the cut, measured perpendicular to the tool axis. It sets how "wide" a pass is, and at low engagement it quietly changes the real chip thickness you're producing — which is why radial chip thinning exists.
Radial depth of cut, also called stepover or RDOC, is the width of material the cutter removes on a single pass, measured across the tool's diameter rather than down its length. At one extreme, ae equals the full cutter diameter — a slot cut, fully engaged. At the other, ae is a small fraction of the diameter — a light, peripheral finishing pass.
This is the part that trips people up: feed per tooth (fz) is what you program, but the actual maximum chip thickness the edge experiences depends on how much of the cutter is engaged. When ae is at least half the cutter diameter (ae/D ≥ 0.5), chip thickness essentially equals fz. But once ae drops below half the diameter, the edge only grazes a shrinking arc of material, and actual chip thickness falls well below fz even though the programmed feed per tooth hasn't changed — that's radial chip thinning.
To keep the real chip load where you want it, manufacturers use the Radial Chip Thinning Factor: RCTF = 1 / √(1 − (1 − 2ae/D)²), valid when ae/D ≤ 0.5. Multiply your target feed per tooth by RCTF to get the feed you should actually program — at very light radial engagement, RCTF climbs sharply, letting you run much higher programmed feed rates without exceeding the tool's real chip load or shortening tool life.