Page 317 - Intro Predictive Maintenance

308 An Introduction to Predictive Maintenance

Figure 14–18 Typical defective gear-mesh signature.

Figure 14–19 Wear or excessive clearance changes the sideband spacing.

Improper Shaft Spacing
In addition to gear-tooth wear, variations in the center-to-center distance between
shafts create erratic spacing and amplitude in a vibration signature. If the shafts are
too close together, the sideband spacing tends to be at input shaft speed, but the
amplitude is significantly reduced. This condition causes the gears to be deeply
meshed (i.e., below the normal pitch line), so the teeth maintain contact through the
entire mesh. This loss of clearance results in lower amplitudes, but it exaggerates
any tooth-profile defects that may be present.