A propeller balancer works by displaying the heaviest blade of a propeller to the balancer operator. Once identified, the heaviest blade of a propeller can be lightened to match a lighter blade or the propeller balancer can show the operator which blade needs to have weight added to bring it up to the weight of a heavier blade. The act of balancing a propeller blade is critical in propeller usage. Without the uses of a propeller balancer, an unbalanced propeller could damage a craft through harmful vibration as well as destroy bearings and oil seals. This could potentially cause an airborne craft to crash and a water-borne craft to sink.
The single- or double-blade propeller is very easy to balance using a propeller balancer. The type of propeller balancer that is perhaps the easiest to use resembles an upside down bicycle front fork with an axle running between the two forks. By placing the axle through the propeller and tightening it into position, the operator then sits the ends of the axle into the slots at the top of the forks. By positioning the blades of the propeller horizontally and letting go of the propeller, the heaviest blade will begin to move downward.
Once identified, the heaviest blade can be lightened to match the weight of the lighter side. In wooden propellers, the heaviest blade can be sanded until it matches the weight of the lighter side. In metal propellers, the hub of the heavy side can have lightening holes drilled into the hub of the heavy blade. After making adjustments to the propeller, it is once again placed into the propeller balancer. This process is repeated until the propeller remains perfectly still when placed horizontally and released.
In some cases, the lighter side of a propeller is weighted with heavy Mallory metal to bring it up to the weight of the heavier propeller blade. This is a rare procedure due in part to the lighter propeller being easier to spin, but mostly due to the very high cost of the heavy metal. When employed, this method is typically done to multi-blade boat propellers. This type of propeller requires a special propeller balancer to effectively do the job.
With propellers with more than two blades, a propeller balancer that operates much like an automobile tire balancer is used. In certain configurations, a bubble-type propeller balancer is employed. By placing the propeller on the hub of the bubble balancer, a bubble similar to a carpenter's level shows the side of the propeller that is heaviest. Manipulation of the other blades or the addition of weight to the lighter blades will bring the propeller into balance.