Convert rim and face dial readings into offset, angularity and front/rear foot corrections for the movable machine.
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Misaligned shafts wear out couplings, bearings and seals. With two dial indicators mounted on the stationary shaft — one on the rim of the movable machine's coupling hub, one on its face — you can measure how far the movable machine is out of line and how much to shim or move each pair of feet. This calculator applies the rim-and-face method: it converts the total indicator readings (TIR) into the offset and angularity at the coupling, then projects them to the front and rear feet using the B and C distances. Work the vertical plane (top and bottom readings) to set shims and the horizontal plane (side readings) to set lateral moves. Positive results mean the feet are high (remove shims) or to the right; negative results mean low (add shims) or to the left.
Check and correct soft foot, and measure the indicator bracket sag so you can correct the rim reading.
Mount both indicators on the stationary shaft: the rim indicator on the outside of the movable machine's coupling hub, the face indicator on its face.
Zero the indicators at one position and rotate 180° to read the total indicator reading (TIR): top/bottom for the vertical plane, side to side for the horizontal plane. Enter the readings with their signs.
Measure A (the diameter the face indicator sweeps), B (rim indicator to the movable machine's front feet) and C (front to rear feet).
Read the front and rear feet corrections: positive = high, remove shims (or right, move left); negative = low, add shims (or left, move right). Correct vertically first, then horizontally, and measure again.
By O.E. — Partner, chairman of the board and CEO of a metal products manufacturer for 21 years; the company exports to 45 countries.
Drafted with AI assistance; calculations checked against primary sources and tested with the site's own code. About FlowUtil
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Both dial indicators are mounted on the stationary shaft. The rim indicator reads the outside of the movable machine's coupling hub; between two opposite positions it sees the centreline offset twice, so offset = rim TIR ÷ 2. The face indicator reads the hub face over a circle of diameter A; the change across that circle is the slope of the movable shaft, so angularity = face TIR ÷ A.
The movable machine's feet are at distance B (front feet) and B + C (rear feet) from the rim indicator. Projecting the offset along the slope gives the correction at each pair of feet: front = offset + slope × B, rear = offset + slope × (B + C). Positive values mean the feet are high (remove shims) or to the right; negative values mean low (add shims) or to the left.
Work the vertical plane (top/bottom readings) to set shims and the horizontal plane (side readings) to set lateral moves, then measure again.
| Symbol | Meaning |
|---|---|
| Rim TIR | Total indicator reading of the rim indicator between opposite positions |
| Face TIR | Total indicator reading of the face indicator between the same positions |
| A | Diameter of the circle swept by the face indicator tip |
| B | Rim indicator plunger to the movable machine's front feet bolt centres |
| C | Front to rear feet bolt centres |
1ACOEM sample data: A = 6 in, B = 7 in, C = 24 in; vertical rim TIR = +24 mils, face TIR = +12 mils.
Offset = 24 / 2 = 12 mils; slope = 12 / 6 = 2 mils/in; front = 12 + 2 × 7; rear = 12 + 2 × (7 + 24)
Front feet = 26 mils high · Rear feet = 74 mils high (remove shims)
Matches the published result (0.66 mm and 1.88 mm in the metric version of the same example). Both pairs of feet must come down, the rear feet much more.
2ReliabilityWeb example: A = 5 in, B = C = 10 in; offset = −10 mils (rim TIR −20 mils), face TIR = +4 mils.
Slope = 4 / 5 = 0.8 mils/in; front = −10 + 0.8 × 10; rear = −10 + 0.8 × 20
Front feet = 2 mils low (add shims) · Rear feet = 6 mils high (remove shims)
Matches the published result. Offset and angularity act in opposite directions here, so the front feet need shims added while the rear feet need shims removed.
If offset and angularity are both near zero, the machines are aligned in that plane. Equal front and rear corrections mean pure offset (shift the machine); different corrections mean angularity (tilt or swing it).
Compare the results with the alignment tolerance for the machine speed and coupling type from the coupling or machine manufacturer, or from ANSI/ASA S2.75 Part 1.
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