In layman terms, backlash is the angular movement (about its axis) between mating parts in an assembly. Backlash occurs in couplings, v-belt drives, gears and other interfacing components. Backlash is desirable in some cases while controlled synchronous drives try to avoid this phenomenon. Even under desired cases, the maximum backlash value is very less to achieve better efficiency. Flexible couplings usually have inbuilt backlash. Even the products that claims zero backlash conceals the condition at which such zero backlash is achieved. It’s always advisable to speak to technical representative to obtain information required. Under operation, the coupling inserts wear out causing more backlashes.
Neoprene and rubber inserts exhibit excessive twisting or visual tooth wear which is a good caution for shaft aligner. Spider-type couplings exhibit excessive compression of the “spider.” On grid-type couplings, inspect for excessive wear of the “spring” type inserts, as well as wear of the grids. On shim-pack couplings, look for wear of the rubber bushings, as well as breakage of the shim packs. Less likely, but just as important, causes of backlash can be improper hub to shaft fits, or excessive keyway wear. Occasionally, backlash can be caused by loose foot bolts or other bolted components.
Backlash can cause erratic shaft alignment values in both dial indicator and laser alignment readings. A backlash of greater than 2° of angular movement should be considered excessive, and should be reduced to less than 2° before alignment begins.
Some methods of controlling and minimizing backlash include:.
•Replacing the worn or defective components in the system which contributes to excessive backlash, such as worn couplings or inserts.
•Minimizing the effects of backlash by rotating shafts to maintain torque at a consistent level and direction. This can be done by rotating the shafts to be measured in a consistent direction, such as clockwise, or counter-clockwise.
•Utilizing temporary mechanical means, such as duct tape or mechanic’s wire, to temporarily override the coupling’s ability to experience backlash.
Remember, most mating rotational systems have a slight degree of backlash, which is both harmless, and desirable for efficient operation. But excessive backlash can decrease the accuracy of your alignment. Keep it to a minimum..