2. To have an equal grip along the entire length of shaft enveloped by the coupling.
3. To have a fastening or locking device of such a nature that it will not be liable to work loose from the torsional strains due to the flexure of the shaft, which is caused by the belts springing or straining the axial line of shafting out of the straight line.
4. To be capable of easy application and removal, so as to permit the erection or disconnection of the lengths of shafting with as little disarrangement of the hangers and bearings as possible, and to be light, run true, and be balanced.
To these requirements, however, may be added that, since it is well-nigh impracticable to obtain lengths of lathe-turned shafting of exactly equal diameter, couplings for such shafting require to fill the following further requirements:
5. The piece or pieces gripping the shaft ends must be capable of concentric and parallel closure along the entire area, enveloping the end of each shaft, and must do this at each end independently of the other, and the piece or pieces exerting the closing or compressing pressure must grip the closing piece or pieces, enveloping the shafting over the entire area.
Fig. 2611.
