Slope of lap 1 in 12.
Fig. 23.
Exercise 20: Solid Butt Coupling.—From the above table of dimensions make a longitudinal and a transverse section of a solid butt coupling for a shaft 2½ inches in diameter. Scale 6 inches to a foot.
Exercise 21: Fairbairn's Half-Lap Coupling.—Make the same views as in the last exercise of a half-lap coupling for a 3-inch shaft to the dimensions in the above table. Scale 6 inches to a foot.
Flange Couplings.—The form of coupling used for the shafts of marine engines is shown in fig. 23. The ends of the different lengths of shaft have flanges forged on them, which are turned along with the shaft. These flanges butt against one another, and are connected by bolts. These bolts may be parallel or tapered; generally they are tapered. A parallel bolt must have a head, but a tapered bolt will act without one. In fig. 23 the bolts are tapered, and also provided with heads. In fig. 14, page 17, is shown a tapered bolt without a head. The variation of diameter in tapered bolts is 3⁄8 of an inch per foot of length.
Sometimes a projection is formed on the centre of one flange which fits into a corresponding recess in the centre of the other, for the purpose of ensuring the shafts being in line.
Occasionally a cross-key is fitted in between the flanges, being sunk half into each, for the purpose of diminishing the shearing action on the bolts.
Exercise 22: Marine Coupling.—Draw the elevation and section of the coupling shown in fig. 23; also an elevation looking in the direction of the arrow. Scale 3 inches to a foot.
The following table gives the dimensions of a few marine couplings taken from actual practice.