which consists of a 2" strip in front and two side pieces that taper from a width of 5" at the face of the house to 2" at the front of the porch. On this frame are nailed the roof boards of the porch. These ought to have an overhang of three or four inches all around, and they will have to be cut away near the house to clear the eaves of the main roof. THE BALUSTRADE At the top and bottom they are fitted between strips B, B, and C, C, to which they are nailed fast. Space the balusters evenly, and the best way of doing this is to fit a measuring-block between each pair before nailing the baluster in place. A fancier balustrade may be made by alternating the pieces A with boards D, D, about 3" wide, as shown in Fig. 17. The top and bottom strips, B, B, C, C, must be two feet long to fit between the posts. The balustrade is fastened to the posts by first nailing blocks E, E, to the posts and then nailing the strips B and C to these blocks. A rail, F, is then nailed on. Nail down a piece of wood about 21⁄2" wide for the sill of the door. The door is then hung on its hinges. (To be continued) THE Construction of the balustrade around the porch is shown in Figs. 16 and 17. The distance between posts should be just two feet. For the balusters we shall need a lot of 1" pieces of wood A. They should be 24" long. BRIDGE-BUILDING FOR BOYS By CHARLES K. TAYLOR MAKING A BOWSTRING SPAN It seems a long time ago now, but once upon a rather exciting time and at a very important point,-right in front of the Hindenburg Line, -Lieutenant Sterns, of the 102d Engineers, ordered a bowstring span made. So an enginer sergeant took a squad or two and built one. He told me about it. Usually, when our boys had to build things in a hurry at the front, they did n't have nicely cut and planed timber waiting for them. They had to take anything they could get, from telegraph poles to remains of sheds, and out of this make whatever was required of them. And they did it! But this engineer sergeant was lucky. He found a lot of cut lumber,-just the stuff for this kind of span,-and in a short time he and his men had it put together and thrown across the canal. It was a thirty-foot span. And for the "bowstrings" he used stuff something like our 2-by-4 lumber, only this was more like 2-by6. It was a very good bridge and very strong, as spans of this kind are when well made. The sergeant showed me the sketches he prepared for it. In fact, he gave them to me, and I showed them to some young men like yourself fellows averaging about fifteen or sixteen years old. And so they thought they would try their hands at it. They got hold of some 2-by-4 stuff. This, as you doubtless know, is lumber 4 inches wide, 2 inches thick, and coming in pieces from 12 to 24 feet in length. The boys found some about 18 feet long, and so decided on a 16-foot span. Now you will see in the photographs that there are two curves in a bowstring span, an upper and a lower one. They are both the same size. If you are to have a 16-foot span, then, to find the curve, you will need a cord twice that length, or 32 feet. In other words, for a bowstring span, to find the proper curve of the main timbers, you will need to make on the ground a circle whose radius is twice the span. So if you have a 10-foot span, there must be 20 feet from the center of the circle to its circumference. If this sounds like too much mathematics, ask your brothers or sisters who are studying geometry to explain. 32 FIG. 1. THE BLACK DOTS INDICATE THE STAKES All right. For a 16-foot span, our boys took a 32-foot cord. One end they tied to a stake in the ground, and with the other end, holding the cord tight, they made a circle, driving in a strong stake every couple of feet. ing, holding this cord straight. (Fig. 1 gives the idea.) Then they moved the stake that had been used as the center of the first circle, and drove it into the ground at a new place on a straight line with its former position, the line passing through the center of the 16-foot curves. Then, when the ends were brought together, a piece of board was nailed to them to hold them in position. This was done at both ends. These two timbers now presented the upper and lower curve of one side of a bowstring span. Then, to hold them in position, they nailed between the two curved timbers uprights made of boards about 6 inches wide and an inch thick. There were three of these uprights, one in the middle, and one each side of the middle, about half-way between that and the end. To these uprights FIRST BOWSTRING SPAN IN POSITION cord and the new place as far from this center as the former place was. From this new place another curve was drawn, connected with the first curve at both ends, and along this curve stakes were likewise driven as before. This gives us now two curves marked out by stakes, and meeting each other at each end of a 16foot line. Now for the fun. The problem was to bend the 2-by-4 timbers around those stakes so that BRINGING THE ENDS OF THE 2-BY-4 PIECES TOGETHER they then nailed another 6-inch-wide board, running from one end of the construction to PRELIMINARY 3-FOOT MODEL OF THE BOWSTRING SPAN the other, thus occupying the middle of what would be one side of the bridge. Upon this piece the floor supports were to be nailed. ter idea of how it looked than I possibly could in words. And, by the way, I should have told you that before they began this job, they made-or rather one young expert did-a little model, three feet long, of the bridge they expected to construct. And this is wise, for it enables one to see the principle of the thing before it is attempted. Well, this bridge they made from that little model was so strong and presentable that our fifteen-sixteen-year group decided to make one equal in size to that big Hindenburg-line one, and even "to go that one a little better" by making it of untrimmed stuff, cut in the woods, Finally, they nailed on two diagonals, as shown in the photograph; and lifted that side up from the stakes and put it aside for a little while. Then they constructed a second side in the same way. Standing this one up on its side, they brought the one previously completed and stood it parallel to the second one, four feet from it and so turned that the two floor-support boards were on the inside. Now they nailed pieces across from the top of one floor support to the other and about a foot apart. This done, they had a series of boards reaching from one side to the other, all on the same level, and on these they nailed two 12-inch-wide boards side by side for the foot-rath. And that virtually completed the 16-foot bridge. Its young builders picked it up bodily, getting a lot of other boys to help, and put it in position. The photograph of it gives a bet SECOND BOWSTRING SPAN IN POSITION, SHOWING PIERS ON WHICH IT RESTS When the first side was completed and stood up, the boys felt proud of themselves. It was "some job." as they declared. The second side bracing between the two sides and below the floor supports to keep the heavy sides from bending inward or outward. These can be early in the photograph of the finished Dridge. All this being done, they called all their friends and by main strength carried this three-ton bridge down to the water's-edge. Now this was to be the end span of a diving pier, the depth of water being about eight feet. It was to rest upon two piers, each made with four corner legs, slanting in, and strongly braced with boards nailed "crisscross." On the tops of the posts, from one to another, were pieces of 2-by-4 stuff for the bridge to rest on. It was quite a task to place these heavy supports in the water, in the proper place, because, when it came to placing the one farthest out, the water was well over the heads of the boys. This was accomplished handily, however, and rocks were piled on top to keep them down until the weight of the span would come into play. Then the crowd, in swimming-tights, lifted the span into the water, where the far end floated, though the shore and reached the bottom. Now to get it on top of the outer support. For this a kind of hoisting apparatus called "sheers" was made. Two long and strong poles were procured, and their tops wired together. To these were fastened a strong chain and also a long, strong wire. These poles were stood up in the water, strad ports. A being ready, the twenty lads gave one strong pull, and up came the far end of the span. When it was high enough, it took only a strong shove in the rear to push it up on the outward support. This being done, the impromptu derrick was removed, and the boys-all of them-standing in the water, lifted the shore end of their span on to the shoreward support. This done, they put down a floor. First 2by-4 timbers were stretched along the floor supports of the span, about 21⁄2 feet apart. Short boards were nailed across from one 2-by-4 to the other, and on these was laid the footway pairs of 12-inch boards placed side by side. And when it was done.-a very beautiful span indeed, and remarkably strong,-the juvenile builders thought they had "gone the Hindenburg Line one better," as they put it, only there were no whiz-bangs or machineguns to make it almost too exciting. Here's the important point for you. The bowstring span is a very beautiful one; it is also very strong and is considered hard to make: but our fifteen- and sixteen-year ladsall six of them-showed what boys of that age can do. Perhaps you might like to take a hand at it yourself. |