Fig. 2617.
In [Fig. 2617] is shown an excellent form of plate coupling, in which most of the requirements are obtained. a and b are the ends of the two lengths of shafting to be connected, c and d are the two halves of the coupling driven or forced on the ends of the shafting, and further secured by keys. The end of one half fits into a recess provided on the other half, so as to act as a guide to keep the shafts axially true one with the other, and also to keep the two halves true one with the other, while drilling the holes to receive the bolts e which bolt the coupling together. The objections to this form are, that it is costly to make, inasmuch as truth cannot be assured unless each half coupling is fitted and keyed to the shaft, and turned on the radial or joint faces afterwards. Furthermore, if the coupling were taken off in order to get a solid pulley on the shaft, the coupling is apt to be out of true when put together again, and, therefore, to spring the shaft out of true. Also, that the bearing, support, or hanger must be open-sided to admit the shaft, and that each coupling, being fitted and turned to its place, would be apt to run out of true if removed and applied to another shaft, whether the same be of equal diameter or not; but if each half coupling be provided with a feather instead of the usual key, the coupling may be readily removed and will remain true when put on again.
Fig. 2618.
[Fig. 2618] represents a plate coupling, in which one end of the shaft passes into the bore of the half coupling on the other length of shaft, which serves to keep the shafts in line one with the other.
Fig. 2619.
[Fig. 2619] represents a single cone coupling composed of an external sleeve having a conical bore and a split internal sleeve bored to receive the shaft, and turned on its outer diameter to the same cone as the bore of the outer or encasing sleeve. The bolts pass through the inner sleeve, the bolt head meeting the radial face of the inner sleeve while the nut meets the radial face of the outer sleeve, so that screwing up the nut forces the inner sleeve into the outer and closes the bore of the former upon the shaft. This coupling is open to the objection that it cannot grip the ends of the shafts equally unless both shafts be of exactly equal diameter, and the bearing on the smaller shaft will be mainly at the outer end only, as explained in [Fig. 2611]. As a result, the transverse strains on the shaft will cause the couplings to come loose in time.