7 Differences Between Soft-Bearing Vs Hard-Bearing Balancing Machines

A balancing machine is a device that is used to balance various rotors to get their vibration and imbalance within the permissible limits.

Balancing machines are used to correct the rotational imbalance of any rotating equipment. This machine is vital in providing a high degree of precision and accuracy in the measurement and correction of the rotational imbalance. The machine typically has two columns with roller bearings or v-support for the rotating assembly to be tested upon.

It also has an accelerometer or pressure transducer on each column which is responsible for measuring the unbalance values or amplitude of vibration. The calculated values are then displayed on a computer monitor or any similar device.

With the rapid industrialization, there has been a rising demand for equipment that ensures that the machine parts are in proper shape. To achieve this, balancing machines use a variety of techniques. As there are various types of products that require balancing, hence, there are also different kinds of balancing machines.

Before delving into the subject matter, let’s see the importance of balancing machines and why it is needed.



Rotating machines are commonly used in the manufacturing of cars, aircraft, electric motors, and many more. If such machines have an unbalance it can result in undesirable vibrations which affect the performance of the machine, increases noise, and also reduces the life of the equipment. To avoid these problems balancing machines are used. It eliminates the unbalance in a rotating machine.

Balancing plays a crucial role in machines, especially in rotating machines like fans, large flywheels, electric motors, pump impellers, turbines, etc. A machine must be balanced to avoid faults. Balancing in machines helps avoid vibration in rotating bodies which can cause a system failure. There are two major types of balancing machines, Soft bearing, and Hard bearing. Neither type is better, each have their strengths and weaknesses.

The balancing machines are responsible for detecting the imbalances that can occur in the rotor, which is then adjusted. The balance is extremely important for any kind of machinery. It ensures that there is no vibration and friction. If a rotor is not balanced properly, this will result in decreased life of the machine and could lead to accidents as well.




Soft Bearing Machines

The soft bearing machine is also called ‘flexible’ because, as the name implies, it is designed to be put almost anywhere without relying on the foundation for support in its measurement process. In soft-bearing balancing machines, the rotor is supported by a flexible column assembly.

The rotor of the soft bearing machine is balanced on its bearings which supports movement in at least one direction. This is generally perpendicular to the rotor axis. In this balancing technique, the rotor acts as if it is suspended in mid-air while measuring the rotor’s movement.

Soft bearing machines can therefore balance most horizontal or flat oriented rotors. These machines are also cost-effective compared to other types of balancing machines.


Hard Bearing Machines

Hard-bearing machines as the name implies are ‘rigid’ because of their style of suspension which is different from the soft bearing machine. They usually require a specialist for the calibration and setting, however, once calibrated will rarely need attention or inspection to be accurate.

The sensors used in the hard bearing columns are fast high gain sensors that can measure unbalance forces very quickly and accurately. Because of the nature of the hard bearing machine they don’t necessarily have to measure movement but can measure pressure or force instead. This allows the machine to retain permanent calibration as the flexible nature of a soft bearing machine will require damping tuning for each type of unique rotating assembly that is mounted. Hard bearing machines, however, can measure a wide variety of parts with a single calibration setup.



The hard-bearing and soft-bearing balancing machines have many similarities; they also possess qualities that bring disparity. Below are the main 8 that make each of the balancing machines unique and distinct:


1. Test Weights

The most critical distinction is that soft bearing machines require the use of test weights during each measurement process. The operator will mount test weights to the rotating assembly at predetermined locations and capture data using the “influence coefficient” method of balancing. This means that the unbalance measurements captured with the test weights will be compared to the measurements without the test weights allowing the computer to calculate the locations for correction. This is a more time consuming method of balancing although it doesn’t rely as much on the accuracy of the machine and electronics.


2. The base

Hard bearing balancing machines have a stationary base, a fixed column that supports the rotor while it rotates at speed , and electronic instrumentation that controls movements of the rotor. Hard bearing balancing machines typically do not use dial indicators, bubblers, or test weights for measurement. They use accelerometers or pressure transducers attached directly to the machine structure and provide a rigid platform where balance correction through drilling or milling can be performed without having to remove the rotating assembly from the machine. Older hard-bearing balancing machines required massive isolated foundations to be build to support the base of the machine, but modern electronics and digital signal processing techniques have advanced such that the control unit can isolate the unbalance data much better and eliminate the need for specialized foundations or anchor requirements.


3. The structure

The structure of a hard-bearing balancing machine is more complex than that of a soft-bearing machine, but it has good rigidity and dynamic performance, high accuracy of correction, long service life and high precision. Some hard-bearing machines utilize crowned rollers to limit the need for careful alignment and precision of the column assemblies. Properly machined column assemblies can still utilize flat bearing rollers.


4. Efficiency

The soft bearing balancing machine is suitable for the general balance test of many types of rotors. The disadvantage is that the process is significantly slower as the operator is required to add test weights, spin up and measure the rotor several times, then remove the test weights, prior to balancing any part.

The hard-bearing balancing machine is suitable for the balance test of various small and medium-sized rotors with low vibration level requirements. The advantage is that it can correct the unbalanced mass on multiple planes at one time, thus improving production efficiency.


5. Cost

Soft-bearing balancing machines are typically more affordable because they do not have to be extremely precise. Hard bearing machines require careful machine work and alignment so that calibration can be retained permanently and accurately which increases the cost of manufacturing.


6. Training

Hard bearing machines are noticeably simpler to use and will require less training for their operators. Soft-bearing machines require more knowledge of unbalance theory and the use of test weights to achieve the best results. Training employees on hard bearing machinery is quicker and less time consuming as the machines are more intuitive to use.


7. Monitoring Large Initial Unbalance

Hard bearing machines don’t require an additional balancing technique to handle applications for large initial unbalance—because of the nature of the rigid design of the machine.
Soft bearing machines design requires additional balancing steps like stopping rotation, locking the rollers, adjusting dampening, selecting larger test weights, and then correcting unbalance.



Balancing machines are used in many industries based on their requirements and speed. The main use is to find out the unbalance in rotors and to rectify the same by adding or removing material from specific locations.

Both types of machines can perform the same jobs for the most part and provide nearly the same level of accuracy, just by different processes.

Hard machines have similar bearings but show some distinction in suspension. These 7 key differences divide each and show their peculiarity. Choosing between hard-bearing vs Soft-bearing balancing machines depends on why you need them.

Understanding the differences is a significant step to making the right choice. ProBal Dynamic Balancing LLC is the market leader in the manufacture of a computerized hard-bearing balancing machines. If you’re still not sure how to choose between soft-bearing vs hard-bearing balancing equipment, contact us today for expert advice!

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