When reporting on mechanical assemblies such as ball screws, gearboxes, reducers and gear motors, often our customers will see notes on the amount of backlash that is present and wonder what that term means. Backlash is a movement or amount of “play” you see in a mechanical system which is caused by a gap between parts that make contact. While in some ways a certain amount of backlash is desirable, too much can lead to a mechanical failure.
What causes backlash?
Backlash can have many causes. One of the major contributing factors is poor lubrication. In a well-built machine, backlash is minimized by design, but a certain amount must be present to allow for lubrication between the moving parts. If lubrication is not present or either poor quality or contaminated the rubbing of parts creates undesired clearances which contributes to adds backlash. Another cause of backlash is poor manufacturing of the gears to begin with, especially when gear teeth are cut too deep. Backlash is also one of those things that increases due to the age of the system.
What failures can happen due to backlash?
Too much backlash in a system can cause many different type of failures. One simple failure is destroying or losing manufactured parts which is a waste of material and time. This is cause by the fact that the machine will no longer be as precise as it once was because the there is a loss of position as it moves in both directions. This loss will cause the machine to travel and undershoot its target position and create undesirable results in what it was designed to do. Other types of failures can be more dramatic such as gear slip and catastrophic mechanical failure.
How is backlash tested for?
Backlash is most often tested by using a precision dial indicator. A “zero” point is found, and the device is measured in both directions of travel. Backlash is measured and compared to OEM specifications to determine if the amount of backlash is within acceptable tolerance.
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