Backlash is the amount of space or clearance between mating gears in a gear train, and is typically created by manufacturing tolerances. Backlash can also refer to the degree of lost motion in a mechanism caused by clearance between parts. Lost motion can cause problems with precision and repeatability, because movement that should be used for one purpose (e.g., feeding stock into a cutting tool) is instead used to take up slack (lost motion).
In general, backlash must be taken up before any loads are applied to avoid transmission of shock loads through the system which could lead to catastrophic failure. When designing or selecting gearing, engineers must carefully consider the amount of backlash that can be tolerated while still maintaining safe operation of the system.
There are a few ways you might be able to fix backlash, depending on the severity of the issue:
-If there is only a small amount of play or lost motion, you may be able to tighten things up by simply adjusting screws or bolts that hold everything in place. This could potentially eliminate all play if done correctly.
-If there is more significant play present, you may need to disassemble part or all of the gear train in order to make shims/spacers to take up some of the slack. Depending on how much play exists, it may not be possible to completely eliminate it this way - but it can often be greatly reduced.
-Another potential solution - particularly if disassembly/reassembly would be difficult - is adding another set of idler gears into the mix (essentially creating an additional stage inbetween two existing stages). This has the effect of halving the distance that each tooth needs to travel per revolution, and can effectively reduce or eliminate backlash altogether.