Hard And Soft Bearing Balancing Machines

Mar 29, 2020

The relationship between types of balancing machines and the standard it follows.

There is confusion between the operational characteristics of these 2 types of machines, the Hard Bearing and Soft Bearing, in relation to the RPM listed on the ISO Standard.

Hard Bearing Machine

The ISO Standard

The Standard states the items’ service speed along with the maximum permissible specific unbalance value to various balancing quality grades.

The Grade is a level of accuracy of balance depending on its function, mass and most importantly, its rotational service speed. The rotational speed specified on this chart/graph is the items’ service speed and bares no relevance to the speed in which the machine balancing this item runs at.

The differences between Hard Bearing and Soft Bearing Machines.

Soft bearing technology

This machine’s pedestals move vigorously side to side as it spins thus exaggerating the actual operational environment. For this method of balancing to work successfully the item must be run at its service speeds. This is because the frequency generated by its pedestals is greater than the frequency of imbalance generated by the item being balanced. When balancing with a soft balancing machine there are several steps and speeds that must be reached until the service speeds are met. It works like this; the machine runs at a certain speed (slower than full service speed) then trial weights are introduced to such time that the machine can run to the items optimum speed. At this time, the item being balanced will have reached a level where the pedestal frequency is less than the residual frequency of the item being balanced.

Hard bearing technology

Hard bearing technology is a more efficient method as the pedestals on this machine do not move or wobble. Thus, forcing the machines sensors to pick up the imbalances in the item being balanced. This is different to the soft bearing machine that picks up the pedestal frequency. In other words, it picks up the pure imbalance of the item without outside influences. This allows accuracy at lower running speeds.


The running speed of a machine should not be confused with the service speeds listed on the ISO Standard. It is the machines technology that determines what speeds it needs to run at to bring the item into Tolerance according to the ISO Standard.

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