Rim-and-face shaft alignment

What this calculator works out

The shims to add or remove and the horizontal moves at the motor's front and back feet, from rim and face dial readings taken at 12, 3, 6 and 9 o'clock, after checking the readings are valid and correcting for bar sag.

The formula in words

First check validity: 12 plus 6 must equal 3 plus 9, on both the rim and the face dial. The offset at the coupling is half the rim reading. The slope is the face reading divided by the face diameter the plunger travels on. The correction at each foot is the offset plus the slope times the distance from the rim plane to that foot, with the sign reversed.

Worked example

• Imperial: rim reads −24 thou at 6, face reads −12 thou at 6 on a 6 in diameter; 7 in from the rim plane to the front feet and 24 in more to the back feet. Offset = 24 ÷ 2 = 12 thou high; slope = 12 ÷ 6 = 2 thou per inch. Front feet: 12 + 2 × 7 = 26 thou high, so remove 26 thou. Back feet: 12 + 2 × 31 = 74 thou high, so remove 74 thou.
• Metric: rim reads +0.24 mm at 6, face reads −0.10 mm at 6 on a 100 mm diameter; 250 mm to the front feet and 600 mm more to the back feet. Offset = 0.12 mm low; slope = 0.10 ÷ 100 = 0.001 mm per mm. Front feet: −(−0.12 + 0.25) = remove 0.13 mm. Back feet: −(−0.12 + 0.85) = remove 0.73 mm.

Watch the simulators explained on the CrewForge YouTube channel, or work through the free sample lesson to see how a full CrewForge lesson is built.