Chap. XI.

MECHANICS.

910

The strength of a gudgeon is limited by thestrain it will bear, and the calculated stressshould include every kind of force acting on theshaft; the diameter should always be determined,so that the gudgeon may be capable of resistingthe whole if occasion required. If w representsthe stress upon the gudgeon in hundred weights,

and / its length in inches, then —^ —

ft

■IP

Fig. 1301.

1 J ,

Fig. 1302.

= or 0-42 (w l)$ = d , the diameter of the gudgeonin inches.

Journals are those parts of a shaft which revolve between the points where the power andresistance are applied, and these have sometimes to carry a fly-wheel, as well as to resistgreat torsion ; to proportion the stress they have to sustain, we must consider the horses-power to which the resistance is equal directly , and the number of revolutions the shaftmakes inversely.

Gudgeons are the ends or extremities of a horizontal shaft which runs in the collar, andin order to avoid friction, are usually made of a diameter as small as possible, so that theirstrength is sufficient. The cube root of the weight of a water-wheelin hundred weights is found to be nearly equal to the diameter ininches of a cast-iron gudgeon sufficiently strong to support it:gudgeons of cast and wrought-iron are in the proportions of 9 to 14;the diameters of journals or gudgeons, when of one or the other,serve, when determined upon, in some degree to proportion the shaft.

The axis of the gudgeon should always be in the line with the axisof the shaft, in order that the motion should be uniform and regular:when the water-wheels are formed of timber, their diameter in feetmust be multiplied by the width in feet, and to this product thesquare of half the diameter must be added. The diameter of thegudgeon in inches will be the cube root of this sum.

Gudgeons when applied to water-wheels, spindles to grindstonesor to other wheels, may be all calculated upon the above principles.

Couplings .may be considered to have either one or two bearings, and serve for the con-veyance of motion by connecting a series of shafts. The square coupling box is the mostsimple, and is formed by making it exactly of the dimensions of the ends of the shaft it is tocontain, so that when motion is given to one shaft it may convey it to the other ; it shouldalso be so contrived that it may be slipped over one shaft, andthe other be disengaged, by which means the motion may bediscontinued. The square coupling box is now only generallyemployed in small machines, and has given way to a cyldrical one, in which pins at right angles arc inserted throngthem into the shaft to hold them firmly together ; thesebe turned with great accuracy, and are found to get out oforder less often than the square coupling.

When a shaft has two bearings, the common coupling usedis that here shown : the shafts are terminated with circularheads, with such alternate indentations, that they not only fit,but give motion to one another; and should any settlementtake place, the joints will not be so much deranged as to mate-rially affect the motion.

In another variety, calculated to connect a long line ofshafts, where there is a heavy strain, Murray’s coupling-box isused successfully; and when the shafts are out of line themotion is continued in the samemanner as by an universal joint.

The two shafts to be united areshown at A and B, and their necksor collars lying on the bearings atC and D. The boxes E and Fare fixed on by wedges, and oneof them has a projecting piece at-tached to both sides of it, as shownat a. The box F has two similarpieces, shown at b, 6. When theshaft A and box Eare turned round,they cut against the screws c, c of

erally__ ' •_,

S 3J h □

" ia y r-dii

Fig. 1303.

Fig. 1305.

3 r 3