Milling feed rate & chip thinning
Turn a chip load (feed per tooth) into a table feed, and correct it for chip thinning when the cutter only takes a light radial stepover.
Safety: chip thinning raises the feed but not the cutter’s strength. On a light hobby mill, cut the result back if the machine chatters, and never exceed the cutter maker’s limits.
How it works, guides and notes
How it works
Feed rate = rev/min × teeth × feed per tooth. When the stepover is less than half the cutter diameter, each tooth enters at a shallow angle and the chip it cuts is thinner than the feed per tooth. Too thin a chip rubs, work-hardens stainless and wears the edge. The chip-thinning factor D ÷ (2√(D·ae − ae²)) raises the feed per tooth so the real chip stays at the thickness you chose.
Worked example: 10 mm 3-flute at 3000 rev/min and 0.04 mm/tooth: 3000 × 3 × 0.04 = 360 mm/min at full width. At a 2 mm stepover the factor is 1.25, so 450 mm/min keeps the same chip.
Where do chip loads come from? Start from the speeds & feeds calculator or the tool maker’s data, then adjust by ear.
Spotted a mistake? Report an error.