What is radial runout on a shaft?

Radial runout (TIR) is the total variation in distance measured from a shaft surface to a fixed reference as the shaft rotates one full revolution. TIR equals twice the eccentricity.

How do I measure runout with a dial indicator?

Mount the shaft on V-blocks, place a dial indicator perpendicular to the surface, zero it, then rotate one full revolution. The total needle movement is the TIR.

What causes excessive radial runout?

Common causes: bent shaft, manufacturing eccentricity, bearing journal wear, improper coupling alignment, and assembly errors.

What is the relationship between runout and unbalance?

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, but measured TIR also includes form error, bend and setup error, so runout and residual unbalance are related yet not equal.

What is acceptable runout for different applications?

The geometric runout tolerance comes from the shaft drawing or the manufacturer's specification, not from ISO 21940-11. As a balance-risk screening value, the unbalance-equivalent TIR is about 40 μm at G6.3 / 3000 RPM, about 3.2 μm at G1.0 / 6000 RPM, and about 80 μm at G6.3 / 1500 RPM. Always calculate for your specific conditions and check the drawing tolerance.

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軸徑向偏擺計算器

估算與您的平衡品質等級和速度對應之 ISO 21940-11 殘餘不平衡限值相符的軸徑向偏擺（TIR — 總指示器讀數），並篩選測得的偏擺以評估不平衡風險。注意：ISO 21940-11 設定的是不平衡限值 — 幾何偏擺公差本身來自軸圖面或製造商規格。

ISO 21940-11 TIR / 偏心不平衡風險篩選

平衡等級 G

運轉速度 (RPM)

軸徑 (mm)

轉子質量 (kg)

測量偏擺 — 選填，用於不平衡風險篩選 (μm TIR)

快速預設

結果

不平衡等效 TIR（篩選值，非幾何公差）

—

允許偏心 (e_per)

—

等效不平衡 (U_per)

—

角速度 ω

—

平衡等級

—

允許偏心

根據平衡品質等級 G 與運轉速度：

G — 平衡品質等級 (mm/s)
n — 運轉速度 (RPM)
ω — 角速度 (rad/s) = 2πn/60

總指示器讀數

由指針式千分表測得的 TIR 是偏心的兩倍（峰對峰值）：

此檢查的範圍： e_每在 ISO 21940-11 中為允許的殘餘 不平衡 （質心偏心），而非幾何偏擺公差。TIR = 2 × e_每因此為一篩選值：若測得的軸頸偏擺超過此值，僅由偏擺引起的質心位移可能已超過所選 G 等級的平衡限值。它不能取代軸圖面上的幾何偏擺公差，且 TIR 較低的軸仍可能不平衡（質量分佈），而測得的 TIR 可能包含形狀誤差、彎曲、軸承安裝或設定誤差，這些並不會一一對應轉化為不平衡。

等效不平衡

實務範例

範例 — 3000 RPM 下的泵浦軸 G6.3

已知： 速度 = 3000 RPM，等級 = G6.3，質量 = 45 kg，直徑 = 40 mm

ω = 2π × 3000 / 60 = 314.16 rad/s

e_每 = 6.3 × 1000 / 314.16 = 20.05 μm

TIR = 2 × 20.05 = 40.1 μm

U_每 = 20.05 × 45 = 902.3 g·mm

不平衡等效偏擺參考表（篩選值）

等級	轉速 (RPM)	e_每 (μm)	等效 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