Tool runout means one flute does almost all the cutting while the others barely engage. This finds the worst-case chip load each flute is really seeing.
Dominant tooth load = programmed chip load + runout. Trailing tooth load = programmed chip load – runout, floored at zero. Both come from the same programmed feed, runout just redistributes the work unevenly between flutes.
How it works
If a tool runs even a couple thousandths off center, one flute sweeps a wider radius and takes nearly all the chip load while the opposite flute can end up rubbing instead of cutting. This shortens tool life and roughens the finish even though the programmed feed per tooth looks fine on paper.
FAQ
How much runout is acceptable? Keeping TIR under roughly 10 percent of the programmed chip load keeps the load split close to even, anything beyond that and tool life and finish start to suffer.
Related Guides
CNC Calculators · Chip Load Calculator · Tool Life Estimator