Logo Picture Left SideLogo Picture Right SideLogo Text at Center

Third Part.

OF OPERATIONS TENDING TO FACILITATE LABOR.

SECTION FIRST.

MACHINES FOR THE RAISING AND REMOVAL OF BLOCKS.

If the workmen are to be believed, the old machines which they are in the habit of using, are, and will continue to be, those best adapted to their wants. But as generations pass away, new ideas take root, and, ere long, the demand will be as great for new machines as it now is for the old ones. There are some, however, that are so good that it would be difficult to replace them with better; among them are the screw-jacks, the cranes for raising, and the carts, hand and wheel-barrows for transportation.

76. Among the first rank in the raising of blocks we find the windlass, and its improvement, the crane, which are much used in the Marble quarries, but rarely for manufactured articles, unless needed to raise them, as in case of monuments or accessories to buildings. They are seldom used in the Marble yards where they would occupy much room; we shall therefore give but a brief notice of them; indeed a detailed description would be unnecessary, as the windlass and crane are familiar to every one.

77. It is well known that the windlass is composed of a cylindrical shaft, of a diameter proportionate to the use for which it is intended, which moves upon its axle by the aid of gudgeons inserted into fixed rests, sometimes in the form of an elongated X, and sometimes mounted upon an inverted T, and wedged upon a sleeper of squared wood or upon strong joists. Some windlasses are moved by cranks, some by wheels, and others by levers.

This may be called the primitive windlass. A cord or chain rolls upon it, and is firmly fixed in the shaft of the windlass, a hook being fastened to the other end, which is attached to the object to be raised.

This has been improved upon, and made more portable and solid, by the substitution of iron or brass for wood, and of gear instead of levers.

For the movement of the windlass, different mechanical apparatus is used, which is usually terminated by a wooden crank having an iron socket which crosses the wooden handle, to which it is fastened by a screw nut. This mechanism is more or less complicated, according to the weight which is to be raised, and the height to which it is necessary to raise it. The simplest apparatus consists of a wheel of a much greater diameter than the cylinder, mounted upon the same axle to which the force acting upon the circumference is directly applied. In this case, the conditions of equilibrium are those of a lever of which the arm of force would be the radius of the large wheel, and the arm of resistance the radius of the cylindrical shaft. The advantage of the power over the resistance can be augmented, by employing a set of windlasses joined together by cords passing around the wheel of one and the cylinder of the other. But instead of employing cords, another method is often used, which makes no change in the conditions of equilibrium between the power and the resistance; namely, notched wheels which work into pinions representing the cylinders.

The axles of these machines may either be parallel to each other, or alternately parallel and perpendicular, following the position of the teeth of the wheels; this method will considerably augment the force of the man, and will prevent many accidents; these, indeed, are almost always occasioned by the unskillfulness of one of the workmen employed; the more the number is limited, the nearer is the approach to unity, and the less are the chances of misunderstanding, and consequently, of accidents which are the frequent results of it.

THE CRANE.

78. This machine is constructed by the union of several simple ones; the lever, the cord, the pulley, and the windlass. The principal piece is a lever of fifteen to twenty feet, according to the use for which it is intended. It is suspended near the middle on an axle or a vertical shaft, which revolves in a circular movement about the point of support. At one end is a pulley or a cable, to which is attached the article to be moved. The same cable is then carried back to the other extremity of the lever, and is communicated to the windlass by which the machine is worked. The weight is not only raised at the pleasure of the workman, but he can also change its position from one place to another, by the movement of the vertical shaft, around which the machinery revolves.

The crane is one of the most ancient vehicles known; it is often improved upon by modifications of the windlass, which is moved sometimes by bars, sometimes by gear, sometimes by horses, and sometimes by steam, according to the demands of the manufactories or quarries by which it is used to ensure the facility of removal of the manufactured articles.-There are many weights which can only be raised by the aid of cranes; its principal use is in extracting, lifting, loading and exporting the blocks of Marble.

THE CRAB.

79. This is more in use among carpenters and masons than among Marble workers, but it is often employed in the quarries, and we shall therefore speak briefly of it.

There are two species; the simple crab is composed of a triangle formed by joining pieces of wood, on the top of which a pulley is placed. The two sides, or arms, are crossed by the axle of a windlass at a certain distance from the base of the triangle, or ground. When a weight is to be raised, the crab is placed in an inclined position, and fastened with ropes attached to the points of resistance. The rope by which the weight is to be raised, is then passed into the groove of the pulley, and rolls itself around the windlass in proportion as the load is raised.

The double crab, which is employed in lifting of heavy masses, is simply the union of two such sets as those of which we have just spoken. The crabs are propped against each other like the two uprights of a double ladder, when they are of equal force and height. In some cases it is more advantageous to have one shorter than the other; they are then joined at the top of the shortest in such a manner that the longest one projecting above, has the effect and supplies the want of the crane. In either case, the power of this machine is in direct proportion with the number of arms which are used and the length of the lever, or the size of the notched wheels and the radius of the windlass.

In heavy works of architecture, or of extraction of stone and Marble, the crab is often replaced by four similar posts, forming a perfect square, and running up to the top of the building. This frame is terminated by two joists, or two stop planks, between which a pulley turns, upon which a cord or chain continually mounts and descends, by means of a windlass placed upon the ground. This frame work has several props upon which men can be placed to guide the movement of the weight. By this means huge masses can be raised and placed as may be wished, almost without effort.

THE WINCH.

80. The Winch is simply a vertical windlass, having a shaft or a conical cylinder, around which a rope or cable rolls, to which the weight is attached which is to be moved to the desired point. It is not used in the workshops, but is an excellent means of approaching the blocks worked, thus avoiding blows and wounds which are often given by the ordinary levers which are used in placing the polished pieces or rollers, or those to be polished in place, after being worked in the yard.

The vertical cylinder is surmounted by a head pierced with holes, in which bars are placed which cross it, and serve to put it in motion by the force of the arm.

The winch varies in form and power, according to the use for which it is designed. There are small ones which, imbedded in the wall of the workshop, in the face of the boards, greatly facilitate the fixing in place of large sized articles.

They may also be used to bind together pieces which are to be joined with mastic, and to keep them in place in such a manner that they may be easily worked, and the welding consolidated. They may also serve as parallel vices, by means of two joists, placed horizontally or vertically, as may be wished. For this is only necessary to lay down one of the stationary joists. They should both have holes in the two extremities, in which a strong cord is passed.

One of the end pieces, in which is a ring, is drawn behind the movable joist by the aid of a pin which is passed in the eye of the cord; the other end is fastened to the hook of the windlass. When the cylinder is put in motion, the movable joist approaches the stationary one, and draws together it the article, the pieces of which are to be pressed. This is a much better method than that of loading the welded pieces with weights to secure their cohesion, and posses the great advantage of neither breaking or scaling them.

We will suppose that a Marble worker wishes to make a vase of a large size; it is to be composed of four, eight, or ten pieces, more or less, which are to be joined by the aid of cement, or mastic, incapable of sustaining the weight of each of these pieces; it is evident that the use of the winch, by drawing to itself the two cords which surround the pieces of Marble, will permit him to work them in place, internally as well as externally, and to hoop them with iron with great precision, if this seems necessary.

THE TACKLE.

81. This machine, which is of prodigious force, but extreme simplicity, is sometimes used in the shops of Marble workers to raise or bring forward pieces of great weight. For this, it must be fixed to a solid post by a ring proportioned to the force of the hook of the tackle, which is usually composed of three or four pulleys in brass or copper, revolving upon the same axle. A movable tackle is usually joined to a stationary one, in such a manner that the same cord may pass in the grooves of all the pulleys. The power should equal the resistance. We find in market tackles, such as weighing machines or steelyards, which are capable of raising six, ten, or twenty thousand pounds.

They are often made to bear up still more. We sometimes hear inexperienced workmen boast of raising blocks of twenty thousand pounds weight with a tackle of twelve; but these are often the victims of accidents which they might have shunned, by not imposing upon their machinery a service for which it was not constructed.

The tackle, when joined with the windlass or winch, will be of the greatest utility in large establishments, as it unites force to precision of movement. Stationed near a machine for finishing large blocks, it greatly facilitates the moving of them to try whether they are properly placed; it is also the means of sparing the strength of the workmen, and guarding them from many accidents.

THE JACK SCREW.

82. The screw is an instrument which is well known in respect to its use, but which is often abused by not proportioning its force to the weight that is to be raised.

Why are they constructed of different sizes? Precisely in order that the workmen may suit them to the uses in which they are to be employed. If they made better calculations as to the weight of the loads, less of these instruments would be broken.

There are several kinds of screws. The simple screw jack is formed of a cap or strong box of oak, hooped with iron, in which a notched wheel moves up and down. On the top of this box is a hole, from which the head of the screw proceeds, which is turned with a pinion notched with teeth, to raise the weight which it is required to displace.

This works admirably when the screw can be placed upon solid earth which will resist the pressure of the weight of the mass; when the ground yields to this pressure, it is necessary to guard against accidents, to place the screw upon a paving-stone, or a flat or square piece of wood, capable of sustaining the resistance of the screw and the weight that is raised.

It is an admitted principle, that the power of this machine is to the resistance, as the radius of the pinion is to that of the crank. The screw is furnished with two important agents: one is a kind of iron shoulder in the form of a strong claw, by which the load is taken almost from the earth and elevated to a certain height; the other is a catch which a bolt fixes after the screw, in order to stop the notched shaft in which it is placed when the weight is elevated to the point at which it rests, which is according to the height of the screw. This catch allows the workman to rest, and gives his assistant time to wedge up either the screw of the mass. When the mass is wedged, it can be easily taken up again, either with the aid of the claw or the head of the screw.

The second species of screw has several toothed wheels furnished with pinions, with the view of augmenting the power of the screw; this is called a compound screw.

The third is the common screw, for firmly fastening trunks, bales, or packets for transportation.

There is still another kind called nut screw, which is employed for the same, or analogous uses.

It is very important, that whoever may use it should not employ it in works exceeding its power, for when its teeth are once broken, bent, or warped, it is repaired with difficulty, and never possesses its original strength.



[Top of Page]