Fig. 1. is an elevation of the Balance-Crane, constructed for building the upper part of the Bell Rock Light-house, when the guy-ropes of the Moveable Beam-crane, became “too taunt,” as sailors express it, or were too near the perpendicular, thereby rendering the machine unstable. To remedy this, the crane alluded to was kept in equilibrium by a back-weight of cast-iron, so adapted as to counteract the varying load upon the working arm or beam. The elevation here represented is the same in principle with that used at the Bell Rock, but differs somewhat in form, agreeably to more recent improvements made in order to adapt it to the erection of the Carr Rock Beacon. a a is the cast-iron foot or socket, into which the upright central column b b is stepped, being a tube of cast-iron put together in convenient lengths, with flush joints, after the manner of spiggot and faucet, fitted by turning and boring. The centre column of this machine might have been carried to any suitable or convenient height, by adding length to length, as the building advanced, without once moving the foot; but at the Bell Rock, not more than three lengths of from 6 to 9 feet were generally in use. c c represent a malleable iron cross-head, which was stepped into the void of the central shaft or column, when the body of the crane was to be elevated. This operation was accomplished simply by hooking the main-purchase and traveller-chains into the eyes c c, when the machinery of the crane was employed with great facility as a locomotive power for lifting itself; d is a stone supposed to be suspended in the purchase-chain; and e is the back-weight or counterpoise, which, at pleasure, was moved horizontally along the balance-beam marked f, consisting of two plates or bars of malleable iron; g is the working-beam, of similar construction; h-h, h-h, h, h, are four of the eight main and secondary suspending ties of malleable iron, applied from above, in order to leave the lower part of the crane unobstructed. This afforded great conveniencey particularly at the Carr Rock, and also at the erection of the Melville Monument of Edinburgh, where the space for the workmen was extremely circumscribed, the shaft of the column not being more than 10 feet 6 inches in diameter towards the top. The main ties h-h, h-h, at the lower extremity, were made fast by the same bolt which passes through the pulleys f and g, while the upper ends were bolted into a collar, which is seen clasping the central column at i i. This collar is fitted with four friction-rollers, one of which is seen at k. l l shew two of the four principal rods or bars of malleable iron for connecting the Crane, and answering the purpose of a king-post to the ties h-h, h-h, of the frame-work; m m mark two of the four braces forming a connection between the main ties and arms or beams of the crane. The cheeks n n n, which contain the train or series of wheels of the crane, are of cast-iron. In the formation of these cheeks they present as little obstruction to the workmen as possible, while, at the same time, they embrace the various journals or axles of the machinery. The upper part is connected by a square framed collar of malleable iron, seen at Fig. 5. fitted with friction rollers, and, like the collar above alluded to, works round the central column. This lower collar is connected with the cheeks of the crane by studs passing through them, and fixed by means of screw-nuts. The lower part of the frame is in like manner connected with the upright shaft, by a collar, which is moveable upon friction-balls of cast-iron, contained in a circular race or chamber o o, a plan of which, shewing the balls, is given at Fig. 3. The whole machine thus fitted, is supported upon the central shaft by means of the cutter or spear-bolt p. The winch handle marked q, is that with which the main-purchase chain r, passing over the pulley s, is worked, from which the stone d is suspended. Connected with the main-purchase, a wheel, marked w, of 30 inches diameter, is worked by a pinion of 5 inches, mounted upon the axle of the handle q, producing a power or force in the ratio of 18 to 1; this power may at pleasure be increased by throwing another pinion on the same axle into gear with the wheel marked n´, of 16 inches diameter.
The handle u u is connected with the main-traveller s, balance-chain v v v, and their traveller x, to which the back-weight e is appended. The main-traveller wheel y measuring 36 inches in diameter, with its pinion of 5 inches marked u, exerting a power in the ratio of 21 to 1, serves to work the main-traveller. On the same axle with the pinion u, is another pinion, working two wheels, as seen in Fig. 4, which gives motion to the balance-traveller. These two combinations of wheels are so arranged, that, by working the small levers m and z, they can with facility be thrown in and out of gear, so as to work the traveller either together or separately. The whole weight of the Balance-crane, here represented as resting upon the oaken beams A A B, on one of the floors, weighed about three tons; but the balance and working beams having latterly been made of malleable iron, and the other parts of the machine considerably lightened, it did not exceed more than two tons in weight when used at the Carr Rock.
Fig. 2. The cast-iron foot of the Crane is necessarily very ponderous, and weighs about half a ton. The toes a a a a extend about 5 feet; b b b b are the bat-holes for fixing it down, in case of its at any time getting off the balance, but, in practice, these bats were seldom applied. When the crane was supported over the void or central holes left in the floors during the progress of the work, the toes were clasped to the oaken beams A A B, formerly noticed, represented as resting on one of the upper floors of the building, B, in Fig. 1., being a cross section of the lower beam, with its levelling-block; c, the socket for the central column, or upright shaft, is 10 inches in diameter at the upper side, and diminishes to 9 inches, that the column may become fixed into it by the pressure of the machine.
Fig. 3. o o, in reference to Fig. 1., represents the collar-chamber, filled with cast iron friction-balls, upon which the body of the machine rested, and traversed horizontally with the greatest facility.
Fig. 4. is a perpendicular section taken across the cheeks and wheels with a view to shew the train of the machine more fully. a a is the foot; b b two lengths of the central column, or hollow cylinder, with their spiggot and faucet joint in the middle, shewing also that the metal is about an inch and a quarter in thickness; c c the cross-head, referred to in Fig. 1.; i i the upper collar, shewing its connection l l with the king-posts or main rods; n n the cast-iron cheeks, with the lower collar, and the chamber for the friction-balls; o the cutter or spear-bolt, which supports the whole machine; u u the traveller handles, the main-purchase handles not being embraced in this section; y y the wheels and pinion of the main traveller; accented y´ y´ the wheel and pinion of the balance-traveller x x. In the central part of this figure, the barrel or drum x of the traveller-chains is seen, and also the middle collar x, with its friction rollers.
Fig. 5. is a plan of the body of the Crane, in reference to Fig. 1. b is a cross section of the central column, seen in connection with the upper collar d d; with a stone suspended from the end of the main-beam; e e the back weight suspended from the balance-beam: f and g the extremities of these two beams; h´ h´ h´ h´ four horizontal braces, extending from the cast-iron cheeks to the middle of the beam. Letters n n n n the cast-iron cheeks of the body; q q the main purchase-handles; r the main-purchase chain; s its traveller; t t the traveller-chain; u u the traveller handles; v the balance traveller-chain; x its traveller; w w the main-purchase wheels; y y the traveller wheels; z the lever, for stopping the main traveller-wheel.
Fig. 6. is a plan of the frame work of this machine: b is the upright column, with the upper malleable iron-collar, shewing its connection with the king-posts l l of Fig. 1.; f and g are the extremities of the main-purchase and balance-beams; m´ m´ the horizontal rods connecting with the main-ties; h h, &c. the main ties; h´ h´, &c. the horizontal braces; n n n n the cheeks or frame of the wheels and machinery, with the two great bolts marked n´ n´, by which the frame was principally connected; these bolts being passed also through the interior ends of the balance and working beams.
Plate XVIII.
GENERAL VIEW OF THE WORKS.
Pl. XVIII.