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Different types of balancing machines

Dynamic balancing machines are mainly classified as hard-bearing or soft-bearing. What does that mean?

A balancing machine is a measuring device for static or dynamic unbalance.
It is designed so that a rotor can be placed on the machine for unbalance measurement. 
The terms "soft-bearing" and "hard-bearing" indicate how the rotor is supported on the pedestals.
A spinning rotor will always try to spin around the mass axis. If the geometric axis (the journal axis) does not coincide with the mass axis, the rotor journals will want to move (vibrate) to let the rotor spin around its mass axis.


Soft-bearing balancing machines

If the rotor support can move freely (soft), the machine is called a soft-bearing balancing machine.
In soft-bearing machines this will lead the rotor support to move (vibrate). The movement is measured with vibration sensors.

Hard-bearing balancing machines

If the rotor is supported in rigid fashion (hard), the machine is called a hard-bearing balancing machine.
In hard-bearing machines the rotor support is rigid. the spinning rotor cannot vibrate; instead the unbalance forces are measured with force sensors (not vibration sensors).

ISO balancing grades, what are they?

The two primary factors to determine permissible unbalance (also called the balancing tolerance) are:

the mass of the rotating part and the maximum operational speed.


Calculating a balancing tolerance based on these parameters is realtively simple. However, these calculated tolerances are for the journal planes, and must be transposed into the correction planes. Based on experimental data, the potential for damage is proportional to the Balancing Quality Grade. Larger G numbers cause more structural stress.

Our Balancing software has a built-in balancing quality calculator for ISO, MIL, API and special standards, like 4W/n and such.

Enter rotor mass, service speed and desired quality grade, and click CALCULATE. The correct unbalance tolerance will be calculated, and automatically transposed from journal planes into correction planes.

ISO 1940 is obsolete and has been replaced with ISO 21940-11, edition 2016-11-15. The EasyBalance software Tolerance Calculator has been updated to this new ISO standard.

Balancing Quality

Balancing Grade G overview

Balancing Quality Grade G number Vibration velocity in mm/s Rotor types - General examples
G 4000 4000 Crankshaft drives for large, slow marine diesel engines (piston speed below 9 m/s), inherently unbalanced
G 1600 1600 Crankshaft drives for large, slow marine diesel engines (piston speed below 9 m/s), inherently balanced
G 630 630 Crankshaft drives, inherently unbalanced, elastically mounted
G 250 250 Crankshaft drives, inherently unbalanced, rigidly mounted
G 100 100 Crankshaft drives of large Diesel engines - Complete reciprocating engines for cars, trucks and locomotives
G 40 40 Crankshaft drives for engines of trucks and locomotives - Cars: wheels, wheel rims, wheel sets, drive shafts Crankshaft drives, inherently balanced, elastically mounted
G 16 16 Parts of crushing machinery - Agricultural machinery - Crankshaft drives, inherently balanced, rigidly mounted Crushing machines Drive shafts (cardan shafts, propeller shafts)
G 6.3 6.3 Fly-wheels Fans - Aircraft gas turbine rotors - Electrical armatures - Process plant machinery - Pump impellers Aircraft gas turbines Centrifuges (separators, decanters) Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds up to 950 r/min Electric motors of shaft heights smaller than 80 mm Fans Gears Machinery, general Machine tools Paper machines Process plant machines Pumps Turbo chargers Water turbines
G 2.5 2.5 Machine-tool drives Computer drives - Turbo compressors - Small electric armatures - Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds above 950 r/min - Gas turbines and steam turbines - Machine-tool drives - Textile machines Turbine-driven pumps
G 1 1 Grinding machine drives - Audio and Video drives - Textile bobbins - Automotive turbochargers
G 0.4 0.4 Gyroscopes - Disk-drives - Spindles and drives of high-precision applications

Dynamic balancing

Knowledge and technology on balancing

Unbalance occurs when the center-of-gravity of a rotating object is not aligned with its center-of-rotation.


Unbalance is caused when the center of gravity is out of alignment with the center of rotation. To correct the problem, a weight of mass m must be attached to the opposite side of the rotating object. Given a rotor mass M and radius R, the following relationship applies.

M (kg) x e (µm) = m (g)  x R (mm)


◇Units Used to Express Unbalance◇

In Terms of the Mass Eccentricity e : µm、mm、cm

In Terms of Mass m : µg、mg、g、kg・・・

In Terms of Mass x Radius (mR) : mg・mm、mg・cm、g・mm、g・cm、kg・cm・・・


Dynamic balancing machines measure the size (magnitude) and angle (direction) of vibration.


There is no limit to the number of products that rotate. Using cars as an example, they consist of tires, shafts, flywheels, gears, and crankshafts, to name just a few. In our homes, we have a variety of equipment, including fans, vacuum cleaners, refrigerator compressors, video heads, DVD and CD systems, and computer hard drives. It would be impossible to count all the types of rotating objects and how many exist.

When these rotating parts or materials rotate, they generate centrifugal forces. Normally, the sum of these centrifugal forces equals zero, however, if they do not, that rotating object will generate vibration and noise. Dynamic balancing machines measure the amount and angle of this vibration.

It means to reduce the amount of unbalance.


Unbalance refers to the center-of-gravity of the rotor being out of alignment with its center-of-rotation (eccentricity). If unbalanced, centrifugal forces will generate vibration and noise during rotation. The world in which we live is overflowing with rotating objects. In most homes, looking around many rooms you can find air conditioners, forced air heaters, or fans, and sometimes even dehumidifiers, humidifiers, or a video, CD or DVD player under the television. In the bathroom you can find washing machine, drier, electric razor, n the kitchen ventilation fans, refrigerators, microwave ovens and in a different room a computer and printer. All of these consumer electronic products include internal rotating parts (motors). Outside the home you see automobiles, which are a dense concentration of multiple rotating objects, as are trains, ships, and aircraft. In manufacturing plants, you can find all types of rotating machinery on a production line. At power plants there are rotating turbines and generators. If all these items were not balanced properly, our lives would undoubtedly be extremely noisy. Furthermore, generating vibration and noise consumes energy, meaning energy is being wasted, which is counterproductive to current efforts to save energy. Not only does vibration waste energy, it causes bearings to wear more quickly and shortens the operating life of products.

The process of reducing the amount of unbalance in rotating items like these is called balancing.

Unbalance created by motion

Dynamic Unbalance
In general, unbalance can occur at any lateral (axial) position along the rotating body and with any magnitude. This unbalance is a combination of static unbalance and couple unbalance and is called dynamic unbalance. The couple unbalance component only appears when the object is rotated, so measuring dynamic unbalance requires rotating the object. Dynamic unbalance must be corrected at two locations in the axial direction (two-plane correction for two-plane unbalance). Put simply, unbalance apparent when the object is perfectly still (no rotation) is called static unbalance and unbalance that becomes apparent after an object begins to rotate is called dynamic imbalance.


 Unbalance Present With Static

Static Unbalance
When a rotor is placed on smooth rails, the heavy side will turn to face downward. The unbalance experienced when an object is static (not moving) is called static unbalance. Static unbalance can be corrected using only one location (one-plane correction for one-plane unbalance).

In terms of eccentric distance, in the range of thousandths of a micron.

Assuming a cylindrical rotor 50 mm in diameter and weighing 300 grams, for example, our standard model could measure a 0.5 mg weight attached to the rotor perimeter.

In comparison, one grain of rice weighs about 20 mg.

This means it can detect an unbalance equivalent to 1/33 of a grain of rice on the surface of a 300 g workpiece roughly the weight of a filled small-beverage can.

The primary cause is an accumulation of error.

There are many factors than can cause dynamic unbalance.

  • For formed or machined parts, potential causes include:
    • Variations in the specific weight of materials
    • Shape is not symmetric with respect to the center axis
    • Variations in forming, machining or other processes
  • For part assemblies, potential causes include:
    • Variations in assembly process
    • Variations in the mass of individual parts
    • Variations in placement