Micro Boring Units: 5 Mistakes Killing ROI (and Fast Fixes)

MBU is a stiffness and stability game. If your bores swing in and out of spec through a shift, look here first.

The five killers

1. Skipping alignment/runout: warm up; verify ≤3 μm at gauge length each shift.
2. Copy-paste parameters: do a 3×3 DOE per material/overhang; lock rough vs finish windows.
3. Starved coolant & chips: through-tool flow aimed at edge; chip-flush cycles for deep bores.
4. Reactive wear changes: life-based offsets and scheduled change points.
5. Wrong geometry & overhang: smaller nose radius, right lead angle, disciplined L/D; damped bars when needed.

Symptoms to catch early

• Roundness lobes (3/4), bellmouth, taper, Ra rings; size walking with temperature.

Quick wins

• Increase bar diameter or shorten overhang; balance to G2.5; avoid running near the bar’s resonance.

Sigma’s role: stability mapping, ZeroSet setup SOPs, RunReady operator playbooks, and probe/gauge integration—so Cp/Cpk rises, Ra stabilises, and life extends without slowing the takt.