Part 6
The solid gutter was now transferred to the hands of the carpenter, who fixed at each end, on the under-side, a small cast-iron shoe; and two struts, nine inches long, were placed so as to divide the whole length into three equal parts--the struts spread out at the top in order to present a large surface of pressure against the under-side of the gutter; and tenons projected upwards, which were fitted into mortices cut into the timber. The lower end of the struts were formed so as to give them a firm hold upon a wrought-iron rod, thirteen-sixteenths of an inch diameter, which was passed under them and through the shoes, where it was screwed up with nuts; and the struts pressing up against the timber produced the requisite bend or camber. Twenty-seven notches, to receive the sash bars, were marked with a templet and cut out on each edge of the upper-side of the gutter; and a small cast-iron plate having been fitted on the under-side at each end, the Paxton's gutter was complete and ready for fixing. The under-trussing of the rafters increased their strength considerably, so that a weight of one-and-a-half tons was required to break one which was experimented upon.
The Sash-bars.
We will next consider the sash-bars which support the ridge of the roof and receive the glass. The total length which was required of these amounts to about two hundred miles; it will, therefore, be easily understood that mechanical contrivance for cutting them out became an absolute necessity; this Mr. Paxton appears to have discovered in his works at Chatsworth, as he mentions in his lecture.
The sash-bars are one inch thick and one-and-a-half inches deep, and are grooved on each side, besides having all the four edges bevelled or chamfered; all which was done in one passage through the machine. The plank which was to form the sash-bars was passed in at one end of the machine, between pressure-rollers; it then passed between cutters placed both above and below it, which made about twelve hundred revolutions per minute, and hollowed out the different grooves; and, lastly, it passed between circular saws which divided it into separate sash-bars, after which they had only to be cut into their proper lengths.[6] The exact length of each sash-bar when finished is four feet one inch.
In this state the skylight bars were sent to the building, where they underwent several finishing operations, necessary to make the ends fit down into the notches prepared in the ridges and gutters. Thirty of the bars were first placed together in a horizontal traversing-frame on a saw-table, on each side of which circular saws were fixed at the distance of the required length of the sash-bar; the frame was then moved forward against the saws, so that both ends of the whole set of bars were cut off simultaneously, and at the same time a cut was made at one end half-way through the bar, in order to form the shoulder against the gutter. They were then removed to another bench, where the end of the bar was bevelled and the shoulder formed by means of a small instrument having a handle with two projecting jaws fitting into the ends of the glass grooves of the bars; between these there was a small blade which, being pressed down, cut out the shoulder which had been sawn through in the other direction, and another blade was placed at the proper angle to remove the bevelled piece at the end of the bar.
One more process made the sash-bars complete for fixing--this was the drilling a hole at each end to nail them down on the gutter and ridge; and this was also done by machinery, to insure all the holes being drilled at the same angle. On one side of a horizontal bench were placed a set of four-inch driving pulleys (_a a_), with as many horizontal drills projecting towards the other side of the bench; a wooden traversing-plate (_c_) opposite each drill, and working towards it, received one end of the sash-bar, while the other rested in an inclined position against a wooden rail (_b_) placed longitudinally above the pulleys, having as many sinkings thereon as there were drills. The traversing-plate being then pushed forward, the sash-bar was perforated by the drill; the plate was then drawn back, and the same operation repeated with the other end of the bar, which left it ready for fixing.
The action of the traversing-plate (_c_) is shown more distinctly in the second engraving.[7] One out of every nine of the sash-bars of the roof is stronger than the rest, to serve for fixing the ridge previous to glazing. These extra-strong bars are two inches wide and one inch and a half deep, and were formed by the same machinery already described, by an adjustment of the different cutters and saws.
The Ridges.
The total length of these required was about sixteen miles. They are cut out of timber three inches square, in section, and are of the form shown in the diagram, with a groove on each side to receive the glass. This was also done by machinery which, with about five-horse power, turned out one hundred lengths of twenty-four feet in a day of ten hours, allowing the time for the necessary stoppages. After they had been delivered at the building, these ridge-pieces were cut to the exact lengths by means of the same apparatus used for the solid gutters which has already been described. At each end of the ridge-piece two holes were also drilled to receive dowells to connect it with the adjoining length. By no other than mechanical means could the immense number of holes thus drilled have been placed so exactly that those in the opposite ends of any two ridge-pieces should correspond precisely.
The different essential component parts of the roof having thus been described, we propose to take the different members of the construction in succession downwards.
The Glass.
But first it may be mentioned here that the glass used throughout the building is sheet, on an average about one-sixteenth of an inch thick, and weighing one pound per foot superficial. This gives an aggregate weight of about four hundred tons for the whole of the work, the greater part of which was supplied by Messrs. Chance and Co., of Birmingham. Each square is forty-nine inches long and ten wide, the greatest length of sheet glass that has ever been made in this country. The manufacture of this kind of glass is of comparatively recent introduction into England, though practised for some time on the Continent; and the rapid progress made by the manufacturers alluded to must be in a great measure attributed to the wise removal of the fiscal burden on the article, made by the late Sir Robert Peel. That lamented statesman, with his usual foresight, doubtless contemplated that great social benefits would follow from that enactment; and it is, perhaps, not too much to say that, but for Sir Robert's enlightened measure, this "huge pile of transparency" would never have been reared.
The Box Gutters.
It has been mentioned that the triple gutters deliver the water into main gutters running in the transverse direction of the building; these are formed of wood, with a bottom piece, into which are grooved two upright sides, they are firmly bolted down upon the upper flange of the roof-girders, and where these are quite horizontal the fall in the gutter is given by a false bottom laid to a slope. Of these gutters there is a length of about five-and-a-half miles in the building, which, added to the aggregate length of the Paxton's gutters, makes a total of about twenty-five-and-a-half miles of gutter.
Roof Girders.
These are of cast-iron, where not more than twenty-four feet long, and the rest of wrought-iron. The cast-iron ones are precisely the same in appearance as those used for the galleries, but lighter in metal; a separate description of them is not, therefore, necessary. The weight of each of these girders is twelve cwt., and each was proved to nine tons previously to being used; but it is calculated that the greatest weight they may have to bear will not exceed five tons: the total number required was about 470.
The wrought-iron girders, or trusses, are partly forty-eight and partly seventy-two feet long, to span the avenues of those respective widths; the principle of the construction is the same in each. The top rail (if it may be so called) of the truss is formed with two pieces of [L section] iron placed back to back [double L sections], and the bottom rail with two flat bars [parallel flat bars], the total depth being three feet; at the ends these bars are riveted on to cast-iron standards, and the intermediate distance is divided into eight-feet lengths by other cast-iron standards, to which the bars are also riveted, and thus a framework of rectangles is formed. In the trusses forty-eight feet span there are, therefore, six such divisions in the length, and nine in those of seventy-two feet span. These are then divided in the direction of ONE of the diagonals by a flat bar passing between and riveted to those forming the top and bottom rails. This completes the constructional part of the truss; but to render the appearance more uniform with that of the cast-iron girders, a flat bar of wood (shown by the dotted lines) is made to form the other diagonal of the rectangles.
The trusses for a span of seventy-two feet are cambered or bent upwards about ten inches, which both adds to their strength and improves the appearance. The form and arrangement of these roof-trusses may be clearly traced in several of the views of the interior which are presented to the reader. The weight, when completed, of each of the trusses of seventy-two feet span is about thirty-five cwt., and of those of forty-eight feet span about thirteen cwt.
It has been already mentioned that four of the roof-trusses vary from the rest on account of the greater load they have to sustain. The depth of these exceptional trusses is six feet, and their length seventy-two feet, or the width of the main avenue, which they bridge over. The principle of their construction is similar to that employed in the lighter trusses; but the arrangement of the parts is somewhat modified. The top rail consists of two pieces of [L section] iron, placed, as before, back to back; but they are further connected on the top by a flat piece [double L sections with flat]. The lower rail is formed by two flat bars placed upright [parallel flat bars], and these are riveted at the ends to standards of cast-iron, which, however, are considerably heavier in construction than those before described; and they have also in the centre, at (_a_) two slots, or sinkings, into which the ends of two of the diagonal bars are riveted. The whole length is then divided into three equal parts, each 24 feet long, by strong CAST-iron standards at (_b_) the ends of which are riveted between the rails, and these spaces are again subdivided into three eight-feet lengths by WROUGHT-iron standards at (_c c_). The top of each standard is next connected with the foot of the next but one to it by diagonal flat bars, which, together with the short pieces fastened into the slots at (_a_), complete the figure of the whole, forming a kind of trellis-work, two diamonds in depth. In the diagram only half the length of the girder is shown.
The dimensions of the different bars of iron in this piece of construction are proportional to the amount of strain they have to bear. The two heavier out of the four trusses just described weighed when completed eight tons each, and the other two, which are of rather lighter construction, six tons each.
The riveting together of the wrought-iron trusses was performed on horizontal supports, on which the curve that they were to be made to was marked out. The bars having been previously cut to the requisite lengths, and punched and drilled with holes for the rivets, were laid out on the stages in the proper forms with the cast-iron standards, which were temporarily kept in place by bolts passed through some of the rivet-holes. The whole framework was then riveted up with red-hot rivets supplied from small portable furnaces, several sets of men being employed upon each truss, by which means as many as sixteen were completed in one day. The whole of the trusses, three hundred and seventy-two in number, required for the building were put together on the ground, and several ingenious mechanical contrivances were made use of to facilitate and hasten the work. To form some idea of the amount of labour that had to be performed, it may be mentioned that each of the trusses forty-eight feet in length, or the smallest, is held together by more than fifty rivets, requiring more than twice that number of holes to be made in bars of iron varying in thickness from a quarter of an inch upwards. About 25,000 rivets were thus required for the whole of the work.
Iron Drilling Machine.
The holes for the rivets were made partly by drilling and partly by punching. In the machine used for the former the bar to be bored was laid upon a flat surface forming part of the solid cast-iron stand of the machinery; the drilling-point worked vertically, and could be moved in that direction to suit the different thicknesses of iron brought under its operation. It was suspended at one end of a lever, with a counterpoise at the other. This lever was also connected by a rod and crank, with another near the ground, one end of which was formed into a tread to be worked by the foot. The workman, when he had arranged the iron in the right position under the drill, pressed his foot upon the tread; thus raising the counterpoise end of the upper lever, and pressing the point of the drill, which was of a spear-head form, down upon the iron. Underneath the iron to be drilled was placed a piece of wood to protect the point of the drill when it had passed through the iron. It was also necessary to moisten the iron during the operation, in order to keep the drill-point cool. Three men were required to attend to this work, which was not so rapid as the other method of making the holes by punching.
The Punching Machine.
The enormous power exerted by this piece of machinery renders it necessary that the stand containing the punch, &c., should be exceedingly solid, and it is formed accordingly by a heavy mass of cast-iron, in which there are two indentations, as seen by the engraving. In the lower of these the punching operation is performed, and in the upper there are shears for cutting off the ends of the bars when required. The motion is communicated to each of these by means of a cogged wheel at the back; but both the punch and the shears work in a vertical direction, slowly moving up and down with irresistible force. There is no sudden blow or jerk, which makes the effect the more striking, as the unpractised eye has no means of discovering the amount of the force which is being put in operation. It is, however, so great that, although the punching of a hole scarcely occupies two or three seconds, the iron becomes quite hot from the effect of the pressure. In using this machine, the workman arranges the iron bar on a solid rest, placing it so that when the punch descends it makes the hole in the position required. As soon as the punch has passed through the bar, the action of the machinery is reversed, and the instrument ascends again; during which time the bar is re-arranged, and the operation is thus continually repeated. This piece of machinery also requires three men to work it, if the bars to be punched are of considerable length, so as to require the ends to be held up; otherwise, one alone is sufficient; and in the course of a ten-hours day about three thousand holes can be punched out--the number, of course, varying according to the thickness of the bars.
Neither of the mechanical contrivances just described are novel inventions, though they are thus, perhaps, brought for the first time under the notice of many of our readers, to whom they may be so far rendered interesting from their being connected with the execution of THE building of the day.
The Adzing and Planing Machine.
At the Chelsea Saw-mills, where the reader has already seen the Paxton's gutters shaped out, another interesting piece of machinery was in use for these works, for the purpose of finishing planks to a certain size and thickness, called the adzing and planing machine. An adze is a tool used by carpenters to remove any unevenness in the surface of a board in a particular spot. In this piece of machinery two cutters are fixed to a revolving arm, under which the plank is made to pass; and as it does so the cutters remove a certain thickness from the whole of the surface. The arrangement of these cutters is very plainly shown in the annexed engraving. On the under-side of the same bench to which this apparatus is fixed, three planes are set, each at an angle of about 5 degrees, by which the under-side of the plank is brought to an even face, while the upper surface is operated on by the adzing-cutters, and in this manner the plank is reduced to an even thickness throughout. As it passes on it is brought between two circular saws, which are adjusted to the width which it is desired to give to the plank. It is dragged forward towards the planes and cutters by means of an endless chain, composed of open links; which chain passes over a wheel provided with projecting pegs, so arranged as to fit into the links. The plank is kept down upon the planes, and otherwise held in position, by pressure-rollers.
The Columns and Connecting Pieces.
The columns in the building perform three important offices. They support the roof and the galleries, and serve as pipes to convey the rain-water from the roofs. Their form, which is beautiful, both mechanically and artistically, was suggested by Mr. Barry; it is a ring, eight inches in diameter externally, the thickness varying in the different columns, according to the weights they have to support respectively. Four flat faces, about three inches wide, are added on the outside of this ring, so that when the column is in its place, they face nearly north, south, east, and west. The column may therefore be considered as a hollow tube, of the section just described, and of the same form at each end, having at its extremities horizontally projecting rings called SNUGS, through which the bolts are passed, to fasten the columns to the connecting-pieces and base-pieces. That the hollow form adopted for the columns is that best suited to obtain the greatest strength with the least amount of material has been abundantly shown by experiments, as even two straws placed in an upright position will bear a very considerable weight; it is that also seen in the structure of the bones of animals. Of these columns there are 3,300 in the whole building.
Those portions of the height of the columns which correspond with the depth and position of the girders form separate lengths, which are called connecting-pieces, as they unite the lengths of columns of the different storeys. These connecting-pieces have the same sectional form as the columns themselves, and, like them, are the same at each end, where there are projections cast on, which serve to support the girders, and which are provided with holes through which the bolts pass to connect them with the columns. These holes alternate with the projections to receive the girders, which projections are so formed that they clip others cast on to the ends of the girders, which will be hereafter described. In the centre of each projection there is formed a small notch which receives the key or wedge for fixing the girders.
The meeting faces of the columns and connecting-pieces were all turned in a lathe, in order that, when set up, they might fit so precisely as not to require any packing to adjust them in an upright position; and only in the cases of those columns which serve as water-pipes is any such packing introduced. In those a piece of canvass, with white lead, is put into the joint. An enormous amount of additional labour was involved by this proceeding, as no less than twelve hundred of such faces had to be operated on; but this did not deter the enterprising contractors, who were fully alive to the importance of the object to be attained. When fixed, the projecting "snugs," with the bolts passing through them, were covered by ornamental caps and bases of cast-iron, fixed after the rest of the work was completed.
The Base Pieces.
The lower storey of columns in every case stands upon base-pieces of which the upright portion is a continuation of the column, with "snugs" at the top, to correspond with those of the column, and standing on a horizontal bed-plate, from which "shoulders" rise to strengthen the upright portion. These bed-plates vary in size from three feet by two feet to one foot six inches by one foot, in proportion to the weight which the several superincumbent columns have to sustain. The longest dimension of the bed-plate is in the transverse direction of the building, in which the greatest overturning strain might be expected to act upon the columns. From the vertical portion of the base-pieces, sockets six inches in diameter project, in the direction of the length of the building, into which are fitted the cast-iron drain-pipes, which convey away the water brought down by the columns from the roof. The height of the base-pieces varies to suit the different levels at which the floor is supported above the ground. These levels had therefore to be determined in every individual instance previous to the castings being made. It was done, however, with such precision that, when they came to be used, they were all found to be of the exact length required for their situation. Of these base-pieces, 1,074 were required for the building.
Cast-iron Girders.
It has been mentioned that the columns supported girders at three different heights, dividing the greatest altitude of the building into three storeys; and that the lower tier of girders, where the building consisted of more than one storey, served to support a gallery.
These gallery girders are all twenty-four feet long and three feet deep, the upper and lower "flanges" or rails having a [T section] formed section with standards at the ends of similar section. The rectangular space between them is then divided into three equal parts, by uprights having a [+ section] form of section, and the three smaller spaces thus obtained have diagonal "struts" in each direction. The girder thus described forms a double truss, in which the diagonal braces are subjected both to the strain of compression and tension. At the top and bottom of the end-standards small projections are cast on, by which the connecting-pieces hold the girders; and at each end of the flat portion of the top and bottom rails small sinkings are cast, by means of which the girder is keyed up to its position. The flat portion of the upper and lower "flanges" of the girder is swelled out in width from the ends towards the centre, in order to increase the quantity of metal in that part where the strain is greatest.