Tool holder balancing (permissible residual unbalance, eccentricity, centrifugal force)
From the balance grade G, mass and spindle speed, this gives the permissible eccentricity e, the permissible residual unbalance U and the centrifugal force it produces. Enter a measured unbalance to see whether it is within the grade.
Holder balance calculator
e = 9549 × G ÷ n (µm) U = 9549 × G × m ÷ n (g·mm) = e × m F = U × 10⁻⁶ × ω² (N) ω = 2π × n ÷ 60
e = 9549 × G ÷ n (µm). The open circle is G2.5 at 20,000 rpm (about 1.2 µm). At the same grade, doubling the speed halves the permissible eccentricity. At around 1 µm the eccentricity is about the same as the position scatter on re-clamping (band), so balancing the holder alone further is undone by the next tool change.
Notes
- This treats the holder as a rigid rotor per ISO 21940-11 (formerly ISO 1940-1). ISO 16084 for rotating tools and tool systems sets the limit from the spindle bearing capacity and the interface fit error, so it is not calculated here. Follow the holder and spindle maker’s tables first.
- At the same grade, doubling the speed halves the permissible eccentricity. A grade only means something together with a speed.
- Catalog figures such as “G2.5 at 25,000 rpm” are for the holder alone as shipped. Adding the tool, collet and nut changes the balance.
- Once the eccentricity is around 1 µm, it is about the same as the position scatter when the holder is re-clamped, so balancing the holder alone further is undone by the next tool change.
See also
All values are guides. Start from the tool maker’s recommended cutting data and adjust for your machine, workholding and coolant. Calculations run in your browser; nothing you enter is sent anywhere.