Gear Problems: Gear Misalignment

Figure 1 - Typical FFT Showing Gear Misalignment

Gear Misalignment - Makes the natural rotation of the gears more difficult since they must fight their way through an area where the gear teeth are misaligned. The causes a momentary binding (slowing) of the rotation. The FFT turns this phenomenon into amplitude peaks at 2x rotational speeds of the gears and 2x GMF. Each of these symptoms - primarily the 2x GMF - may indicate a gear alignment problem (which may, of course, be induced with poor coupling alignment or other external factors such as soft foot).

Gear Misalignment Symptoms: Highest amplitudes at 2x GMF. Amplitude peaks at other GMF harmonics - 1x, 3x, etc. High amplitude sidebands particularly around 2x GMF at 1x or even 2x rpm. Shaft running speed harmonics - 2x and even 3x rpm. Recommended Actions: Inspect gears for wear patterns misalignment causes uneven wear. Check for external problems - shaft alignment, soft foot, etc.