BIZOMAT MAKEOS · Maintenance
Rim and Face Shaft Alignment Corrections
How many shims should go under each foot of the movable machine to correct this misalignment?
Vertical (or horizontal) offset and angularity from rim and face dial indicator readings, and the correction at the front and back feet of the movable machine.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Rim reading at 6 o’clock (zeroed at 12) | mm | Total indicator reading on the movable coupling rim at the bottom, with the indicator on the stationary shaft and zeroed at the top (plunger in = positive). |
| Face reading at 6 o’clock (zeroed at 12) | mm | Total indicator reading on the movable coupling face at the bottom, zeroed at the top (positive = gap closed at the bottom). |
| Diameter of the face reading circle | mm | Diameter of the circle the face indicator tip traces. |
| Coupling to front foot of movable machine | mm | Axial distance from the coupling face (indicator plane) to the movable machine’s front feet. |
| Coupling to back foot of movable machine | mm | Axial distance from the coupling face to the back feet. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Rim reading at 6 o’clock (zeroed at 12)
- What it is
- The total dial indicator reading on the rim of the movable machine’s coupling half at the bottom, with the indicator mounted on the stationary shaft and zeroed at the top.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The correction at both feet changes by half of any change in this reading.
- Get it right
- Use the sign convention stated by the tool: plunger pushed in reads positive. The offset is half this reading.
What this means: Face reading at 6 o’clock (zeroed at 12)
- What it is
- The total dial indicator reading on the face of the movable coupling half at the bottom, zeroed at the top; positive means the gap is closed at the bottom.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It sets the shaft slope, so its effect on the correction grows with the distance to each foot.
- Get it right
- Watch the sign: a positive reading means the faces are closer at the bottom than the top.
What this means: Diameter of the face reading circle
- What it is
- The diameter of the circle traced by the face indicator tip as the shafts are rotated, used to turn the face reading into a slope.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger face circle reduces the slope worked out from the same face reading.
- Get it right
- Measure the actual circle the tip traces, which may be smaller than the coupling diameter.
What this means: Coupling to front foot of movable machine
- What it is
- The axial distance along the shaft from the coupling face, where the indicator reads, to the front (inboard) feet of the movable machine.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure to the centre of the foot bolts, along the shaft axis.
What this means: Coupling to back foot of movable machine
- What it is
- The axial distance along the shaft from the coupling face to the back (outboard) feet of the movable machine.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 650 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure from the same coupling face as the front distance, not from the front feet.
Method and formulas
- Offset = rim ÷ 2 (positive: movable shaft low at the coupling).
- Slope = face ÷ face diameter (positive: movable shaft slopes down away from the coupling).
- Correction at a foot = offset + slope × distance to that foot; positive = add shims (raise), negative = remove.
- Example: rim 0.3 and face 0.1 mm: add 0.35833 mm at the front feet and 0.69167 mm at the back feet.
Limitations
- Sign convention as stated (indicator on stationary shaft, readings on the movable coupling); check yours before moving the machine.
- Indicator bracket sag, soft foot and thermal growth are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Calculate shim changes after taking rim and face readings
- Calculate horizontal moves from side readings
- Check alignment before and after correction
Who it is for
- Maintenance engineers
- Reliability engineers
- Maintenance technicians
What you get
- Offset at the coupling
- Angularity (slope)
- Shim change at the front and back feet
Interpreting the result
- Correct soft foot first, then vertical, then horizontal; re-read after each move.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2645–2650. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
The rim and face method
In Shaft Alignment by the Numbers
What it covers: How rim and face dial readings give offset and angularity at the coupling, how similar triangles turn them into corrections at the feet, and how to check the signs before moving.
Useful alongside · BIZOMAT original book
Keep running belt spans out of resonance
In Vibrating Machine Elements by the Numbers
What it covers: Work out tight-side and slack-side span frequencies under load and belt speed, map them across the drive range and decide what to do where harmonics cross.
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