Shaft Alignment Calculator: Face-Rim and Reverse Indicator

Without a laser system, alignment is done with dial indicators. The face-rim method reads the coupling face and rim; the reverse indicator method reads the rim of both shafts. Enter the readings and see the foot corrections.

Face-Rim Reverse Indicator

Units

Rim readings

Top 12 Right 3 Bottom 6 Left 9

Face readings

Top 12 Right 3 Bottom 6 Left 9

Face reading diameter

Distance to front feet Distance to rear feet

Vertical sag

Enter readings so that they describe the moving machine centreline relative to the stationary one: zero at 12 o'clock; positive bottom and right readings mean the moving shaft is low and to the right. Distances are measured from the coupling (face-rim) or plane A (reverse).

Front feet — vertical: —
Rear feet — vertical: —
Front feet — horizontal: —
Rear feet — horizontal: —
Vertical offset: —
Horizontal offset: —
Vertical angularity: —
Horizontal angularity: —
Reading closure (T+B)−(R+L): —

Moving machine centreline (exaggerated) and foot corrections

These tools are intended for preliminary assessment and training. Decisions on critical equipment should be based on on-site measurement and expert evaluation.

How to use

Choose the method and units.
Zero the indicators at 12 o'clock and take readings at 3, 6 and 9.
Enter the distances from the measuring plane to the front and rear feet; correct vertically (shims) first, then horizontally, and measure again.

Theory & formulas

Offset (from rim readings): δ_V = (Bottom − Top)/2, δ_H = (Right − Left)/2; sag is subtracted from the vertical value.

Face-rim angularity: α = (face bottom − face top)/D. Reverse indicator: α = (δ_B − δ_A)/S.

Foot correction: Δ(x) = −(δ + α·x), with x the distance from the measuring plane to the foot. A positive vertical value means add shims, negative means remove shims.

Valid readings satisfy Top + Bottom ≈ Right + Left; a large difference points to bracket sag, play or a reading error.

Frequently asked questions

Face-rim or reverse indicator?

Reverse indicator reads the rim of both shafts, so it is not affected by axial float and is more accurate on long spacer couplings. Face-rim is practical on short couplings and when one shaft cannot be turned.

What tolerance should I aim for?

It depends on speed; at 1500 rpm typically 0.05–0.10 mm offset and 0.05–0.08 mm/100 mm angularity. See the shaft alignment tolerance tool in the lab.