🎯 Shaft alignment basics

Types of misalignment

• Offset (parallel): centrelines are parallel but not in line.
• Angular: centrelines meet at an angle.
• Real misalignment is usually both, in the vertical and horizontal planes. Check and correct vertical (shims) first, then horizontal (moves).
• Move the machine that's easiest to move (usually the motor) and keep the other as the stationary machine.

Before you align

• Lock out and verify both machines.
• Check for pipe strain and base problems.
• Soft foot: with all feet tight, loosen one foot at a time with a dial or feeler gauge on it. Movement means that foot isn't sitting flat. Fix it with shims before aligning. Many shops use about 0.002 in (0.05 mm) as a limit; follow your site's spec.
• Check shaft and coupling runout, and clean the feet and shims.

Rim and face readings

• Zero the indicator at the top (12 o'clock) and read at 3, 6 and 9. The sides should add up to the bottom reading (validity rule: top + bottom = left + right).
• Rim: the actual centreline offset is half the total indicator reading (TIR), because the indicator rides on both sides of the shaft.
• Face: angularity (slope) = face reading ÷ the diameter the indicator tip swept.
• Account for bracket sag on rim readings. Measure it on a pipe or bar first.

Working out foot corrections

Corrections use similar triangles. At each foot of the movable machine, the move is the offset at the coupling plus the slope multiplied by the distance from the coupling to that foot. Watch the signs (high or low, toward or away) and draw a sketch. Allow for thermal growth if the machine runs hot. Laser systems do the same math for you.