Free Engineering Tool
Shaft Radial Runout Calculator
Estimate the shaft radial runout (TIR — Total Indicator Reading) that corresponds to the ISO 21940-11 residual unbalance limit for your balance quality grade and speed, and screen measured runout for unbalance risk. Note: ISO 21940-11 sets unbalance limits — the geometric runout tolerance itself comes from the shaft drawing or manufacturer specification.
Results
Permissible Eccentricity
From the balance quality grade G and operating speed:
- G — balance quality grade (mm/s)
- n — operating speed (RPM)
- ω — angular velocity (rad/s) = 2πn/60
Total Indicator Reading
TIR measured by a dial indicator is twice the eccentricity (peak-to-peak):
Scope of this check: eper in ISO 21940-11 is a permissible residual unbalance (mass-centre eccentricity), not a geometric runout tolerance. TIR = 2 × eper is therefore a screening value: if measured journal runout exceeds it, the mass-centre displacement from runout alone could already exceed the balance limit for the selected G grade. It does not replace the geometric runout tolerance on the shaft drawing, and a shaft with low TIR can still be out of balance (mass distribution), while measured TIR can include form error, bend, bearing seating or setup error that does not translate one-to-one into unbalance.
Equivalent Unbalance
Practical Example
Given: Speed = 3000 RPM, Grade = G6.3, Mass = 45 kg, Diameter = 40 mm
ω = 2π × 3000 / 60 = 314.16 rad/s
eper = 6.3 × 1000 / 314.16 = 20.05 μm
TIR = 2 × 20.05 = 40.1 μm
Uper = 20.05 × 45 = 902.3 g·mm
Unbalance-Equivalent Runout Reference Table (screening values)
| Grade | Speed (RPM) | eper (μm) | Equivalent TIR (μm) |
|---|---|---|---|
| G6.3 | 750 | 80.2 | 160.4 |
| G6.3 | 1500 | 40.1 | 80.2 |
| G6.3 | 3000 | 20.1 | 40.1 |
| G2.5 | 3000 | 7.96 | 15.9 |
| G2.5 | 6000 | 3.98 | 7.96 |
| G1.0 | 6000 | 1.59 | 3.18 |
| G1.0 | 12000 | 0.80 | 1.59 |
Radial runout (TIR — Total Indicator Reading) is the total variation in distance measured from a shaft surface to a fixed reference point as the shaft rotates one full revolution. It indicates how much the shaft deviates from perfect concentricity. TIR equals twice the eccentricity.
Mount the shaft on V-blocks or between centers, place a dial indicator perpendicular to the shaft surface, zero the indicator, then slowly rotate the shaft one full revolution. The total needle movement (max minus min) is the TIR.
Common causes include:
- Bent shaft from thermal distortion or impact
- Manufacturing eccentricity (turning error)
- Bearing journal wear or damage
- Improper coupling alignment
- Assembly errors (misaligned press-fit components)
If the mass centre of a rotor is displaced by eccentricity e, the equivalent unbalance is U = e × m, where m is rotor mass. Journal runout can displace the mass centre and thus contribute to unbalance. However, not all unbalance comes from runout (mass distribution matters too), and measured TIR can include form error, bend, bearing seating or setup error that does not translate one-to-one into unbalance.
The geometric runout tolerance comes from the shaft drawing or the manufacturer's specification — ISO 21940-11 sets unbalance limits, not runout tolerances. As balance-risk screening values (TIR equivalent to the residual unbalance limit):
- G6.3 / 3000 RPM: TIR ≈ 40 μm
- G1.0 / 6000 RPM: TIR ≈ 3.2 μm
- G6.3 / 1500 RPM: TIR ≈ 80 μm
Always calculate for your specific conditions and check the drawing tolerance.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Achieve ISO 21940-11 balance quality on-site. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
