A ball nose end mill cuts with a hemisphere, and that single geometric choice rewrites every number on the setup sheet. The fix is geometry, not feed rate. • Effective diameter governs everything. For an axial depth ap on a ball of radius R, D_eff = 2 x sqrt(2Rap - ap^2). At 0.2 mm depth a 10 mm ball engages only 2.8 mm of diameter, so real surface speed is under a third of the nominal figure. • Tilting the spindle 10 to 15 degrees on a five axis machine shifts the contact patch clean off the dead centre, restores cutting speed and loads a stronger section of the flute. • Stepover sets finish. Residual scallops between adjacent passes stand at h = ae^2 / 8R, so halving the stepover quarters the cusp height. A 0.2 mm stepover with a 10 mm ball leaves a one micron ridge, which is why finishing paths crawl across a surface in fractions of a millimetre. The tooling is a century of metallurgy. Karl Schroeter patented cemented tungsten carbide at Osram in 1923, commercialised by Krupp...