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Shaft alignment is the positioning of the rotational centers of two or more shafts such that they are co-linear when the machines are under normal operating conditions. Proper shaft alignment is not dictated by the total indicator reading (TIR) of the coupling hubs or the shafts, but rather by the proper centers of rotation of the shaft supporting members (the machine bearings). Some coupling manufacturers have designed their couplings to withstand the forces resulting from as much as3 degrees of angular misalignment and0.in. ( mils) of offset misalignment, depending on the manufacturer and style of the coupling. Another common tolerance from coupling manufacturers is the gap tolerance. Typically this value is given as an absolute value of coupling face TIR (as an example, a specification migh read “face TIR not to exceed0. in.”)
