Shaft Alignment Fundamentals: Why It Matters and How to Do It Right

Shaft misalignment accounts for over 50% of all rotating machinery breakdowns. Even 0.002" of misalignment can dramatically reduce bearing and coupling life. Here's how to get it right.

Types of Misalignment

There are three types of shaft misalignment between a motor and driven equipment:

• Angular misalignment: Shaft centerlines intersect at an angle. Causes: uneven shimming, thermal growth, foundation settling
• Parallel (offset) misalignment: Shaft centerlines are parallel but offset. Causes: incorrect motor positioning, worn mounting surfaces
• Axial misalignment: Shafts are pushed too close or pulled too far apart. Causes: thermal expansion, incorrect coupling gap

Most real-world misalignment is a combination of all three types.

Why Misalignment Kills Machines

Even small misalignment creates enormous forces on bearings, seals, and couplings: - Bearing life can be reduced by 50% with just 0.005" misalignment - Coupling life drops exponentially with increasing misalignment - Seal failures lead to lubricant loss and contamination - Energy consumption increases by 2-17% - Vibration causes fatigue failures in shafts, bolts, and foundations

Detection Methods

• Straight edge and feeler gauges: Quick check, accuracy to ~0.005". Good for rough alignment
• Dial indicator method: Rim-and-face or reverse indicator. Accuracy to 0.001". Industry standard for decades
• Laser alignment: Most accurate (0.0001"), fastest setup, compensates for thermal growth. Recommended for precision applications

Alignment Procedure (Simplified)

1. Check and correct soft foot (all four motor feet must sit flat) 2. Rough-align the motor by eye or straight edge 3. Measure angular and offset misalignment at 12, 3, 6, and 9 o'clock positions 4. Calculate shim corrections for the front and back feet 5. Make horizontal corrections by repositioning the motor 6. Re-measure to verify alignment is within tolerance 7. Document the final alignment readings

Alignment Tolerances

For 1800 RPM machines, typical targets are: - Angular: less than 0.001" per inch of coupling diameter - Offset: less than 0.002" - For higher speeds, cut these values in half

Service Bearing provides alignment tools, training, and onsite alignment services throughout Southern California. Call us for your next alignment project.