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Lindskog Balancing
1170 Massachusetts Ave
Boxborough, MA 01719
(978) 263-2040
(978) 263-4035


What is and what causes unbalance?

Unbalance is a lack of evenly distributed mass about the axis of rotation of a rotating element. Causes of unbalance include balance tolerances in manufacturing and assembly, density variations in materials, nonsymmetrical designs, and distortion in operation.

What are the benefits of balancing?

Balancing minimizes vibration, increases bearing and machine life, reduces noise, reduces power losses, improves quality, and increases customer comfort and satisfaction.

How is balancing performed?

In most cases, weight is either added or removed from the rotating element. The process may include drilling, grinding, milling, bolting, welding, or gluing material.

Should a rotor be brought to Lindskog Balancing or can it be balanced in place?

Rotors that are too large to be shipped or are simply impractical to send to us can usually be balanced in place. In some cases, it is more economical to send the rotor to us for balancing, especially if the rotor requires intricate corrections. Access to the rotating component at your facility is usually the determining factor for sending the part to us as corrections may be difficult or impossible without access.

How fast is a part spun to be balanced?

A rotor that is considered rigid is spun only as fast as the balance machine needs for sensitivity. A non-rigid rotor needs to be spun at operational speed due to changes that occur to the shape of the rotor at speed.

What is Whip balancing¬Ě?

Whip balancing rotors involves balancing the rotor as well as preventing the deflection of the rotor at speed. Whip frequently occurs in long shafts that operate at, or near their critical speed. It is also known as resonant frequency.

What is critical speed or resonant frequency?

All rotors have a resonant frequency. The resonant frequency is the speed in cycles per minute at which a rotor will vibrate if struck in such a way as to create a vibration. Think of a ruler hung off the edge of a desk and then struck. If most of the ruler is off the desk, the frequency will be low and the amplitude will be high as there is a lack of rigidity. If very little of the ruler extends beyond the desk, the frequency will be high and amplitude will be low since the rigidity increases. The critical speed of a shaft is based on the resonant frequency and will most likely deflect at this speed even if well-balanced.

How is balance tolerance calculated?

Total Residual Unbalance (gr.-in.) = Rotor Weight (grams) x ISO Quality Grade x 0.3759/ Maximum RPM.

What are ISO balance quality grades?

Balance quality grades are categories which rotors are classified. The grades begin at G-0.4 and progressively increase at a factor of 2.5. Each increase in quality grade results in greater balance tolerance. Rotors such as high-precision grinding machine spindles may be classified as G-0.4, whereas, general machinery components such as rubber covered idler rolls may be classified as G-6.3. Only the lowest four quality grades are typically used in balancing. They include G-0.4, G-1.0, G-2.5, and G-6.3.

Why not use only the lowest quality grade for balancing?

There are reasons ISO G-0.4 is not practical for all applications. The requirements to achieve ISO G-0.4 are that the rotor be mounted in its own bearings and housings, operate under the actual service conditions, and self-driven. Unless the rotating component requires this level of precision in operation, it is simply not necessary to achieve a balance tolerance that meets ISO G-0.4.

What is needed for engine balancing?

We need the pistons and rods, disassembled, along with the crankshaft, piston pins, a set of piston rings, a set of connecting rod bearings, damper and pulley, if applicable, flywheel or flexplate, if applicable, clutch disk, and pressure plate. Harley Davidson crankshafts need to be supplied assembled and trued without the connecting rods attached.