If a sleeve have a single split, the manner in which it will grip a shaft smaller than the sleeve’s bore depends upon the manner in which the compression is effected.
Fig. 2615.
Fig. 2616.
In [Fig. 2615], for example, is a ring supposed to be compressed by a pressure applied at a and at b, causing the ring to assume the form shown by the dotted lines. The centre of the ring bore would therefore be moved from c to d. Now, suppose that the end of one section of shafting were to fit the sleeve bore, then compressing the sleeve upon it would not practically move the centre of the bore; but if the shaft at the other end of the sleeve were smaller than the sleeve bore, the compression of the sleeve to grip the shaft would move the centre of the bore, and, therefore, of the shaft towards d, hence the axial lines of the shafts would not be held true one with the other. To accomplish this latter object, the compression must be equal all round the sleeve, or it may be applied at the points e and f, [Fig. 2616], although it is better to have the compression area embrace all the circumferential area possible of the sleeve, and to have the movement that effects the compression simultaneous and equal at all points on the circumference of the ring or sleeve, because if these movements are independent, more movement or compression may be given at one point than at another, and this alters the centre of the bore; thus, if more pressure were exerted at e than at f, in figure, the centre of the bore would be thrown towards f, or vice versâ. If the pressure be concentric, the single split ring or sleeve grips the shaft all round its circumference; hence it is only necessary in this case to maintain the circumference of the sleeve in line to insure that the shaft ends be held axially true one with the other; and if the pressure on the ring be applied equally from end to end its closure will also be parallel and equal, and the shaft will be held with equal force along that part of its length enveloped by the coupling. It is obvious, however, that the piece or sleeve gripping the end of one shaft must be independent of that gripping the other, so as to avoid the evils shown in [Fig. 2612], while at the same time the casing or guide enveloping the two independent rings or sleeves must guide and hold them axially true, one with the other.
