CNC Spindle Vibration Severity Tracker

Per ISO 10816, up to 1.4 mm/s RMS is new-machine condition (zone A) and up to 2.8 mm/s is acceptable for unrestricted long-term operation (zone B). Between 2.8 and 4.5 mm/s the machine should be scheduled for corrective maintenance (zone C), and above 4.5 mm/s vibration is severe enough to cause damage (zone D).

The tooling. If bare-spindle vibration sits in zone A/B but jumps with a specific holder or tool, suspect tool/holder imbalance, a dirty or fretted taper, or excessive stick-out. Balance holders to G2.5 at operating speed for high-speed spindles, and clean tapers every change.

On the spindle housing nose, as close to the front bearing set as possible — as close to the bearing as possible, on stiff metal (never on covers or guards). Take horizontal, vertical and axial readings if you can; use the highest for the ISO grade and always re-measure at the same spot, load and speed.

The usual suspects are tool/holder imbalance, drawbar or taper contact loss, front-bearing wear and belt or coupling faults on belt-driven spindles. A frequency spectrum tells them apart: imbalance shows at 1× running speed, misalignment at 2×, bearing defects at non-synchronous frequencies, and looseness as a raised noise floor with harmonics.

Velocity in mm/s RMS, 10–1,000 Hz. ISO 10816 zone tables are defined on broadband RMS velocity because it weights low- and high-frequency faults evenly for general machines. Acceleration (g) suits high-frequency bearing analysis and displacement (µm) suits low-speed machines, but neither maps onto these zone boundaries.