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low and consequently easy to heat, and, as has been said, with good illumination over the entire floor.

The essential feature of the saw-tooth construction consists in forming the roof in broken sections, the roof proper having an inclination of about fifteen degrees, and the glazed portions an inclination of about sixty degrees.

Fig. 16 is a longitudinal section and Fig. 17 a transverse or cross-section of a machine shop with this type of roof, the construction being of steel. Fig. 18 and Fig. 19 represent a similar roof with wood used in its construction instead of steel. In Fig. 20 is given a perspective view of the machine shop when finished, showing the general arrangement of the high central portion and the lower portions at each side.

The side walls are built in the usual manner, with pilasters to strengthen them. They are pierced for windows on the same general plan as in the previously described buildings.

The plan of the building is the well-known one wherein a high central space is provided for an erecting floor, over which a heavy traveling crane is mounted, covering every part of this floor. The sides of this building, where it reaches above the side portions, may be planked up and covered with tarred paper and then tin, or, still better, with the specially stamped sheet steel. Corrugated steel or iron is sometimes used. Either of these plans will answer

the purpose.

The side portions are built considerably lower as the same height is not here necessary or desirable. These portions are provided with smaller traveling cranes, running upon I-beams or girders which project into the central space, as shown in Fig. 17, so that these cranes are capable of depositing their loads within the reach of, and under, the main crane.

If much heavy work is to be done, each of the bays, on both sides of the central portion, is supplied with one of these cranes, as shown in Fig. 16 and Fig. 17. By this means any load

may be quickly and conveniently transferred from any one point, within any one of the bays to any point within any other bay, or to any point in the central erecting space, by the combined use of the main and secondary cranes.

In many cases it will be necessary to have these secondary cranes on one side only of the central space, the other side portion being reserved for machines and work of a lighter description. So, also, it may not be necessary to equip all the bays on one side, even, with secondary cranes, while it may be necessary, and very convenient, to so equip several bays in this way. The nature of the work may be such that it will be convenient to equip several bays on each side and at one end with secondary cranes so as to arrange all the heavy work across the end of the shop instead of along the side.

As a matter of course, if traveling cranes are to be used over the bays

we must provide such a system of driving power as not to interfere with them. Shafting may be used near the side walls for driving machines under it or near to it, but the main dependence will have to be the electric system, which, with separate motors for each machine, or one motor for a group of machines located closely together, seems to be the favorite method of driving.

Fig. 16 shows the most approved form of truss for supporting this type of roof, and Fig. 17 gives the form of girders used to support the ridges of the roof where the glazed portion joins the roof proper. This construction is of light structural steel and no more members are used than is absolutely necessary, hence the entrance of light is very slightly interrupted and still there is sufficient strength for all practical purposes.

The glazing of the light portions should receive much attention, in order to avoid leakages, as this is always one of the drawbacks of any kind of inclined windows.

For purposes of ventilation the sashes may be hinged at the top and opened by any convenient means. A simple device is to run a light shaft along inside the building and near the bottoms of the sashes, and fix to it cast iron arms, in the form of cranks, for each sash. From these arms connecting rods run to the sashes. This shaft may be operated by fixing to it a grooved pulley, over which a small rope runs, and reaches down near the floor, from which it may be operated. Levers standing in opposite direction on this shaft, and having a cord attached to each end, may be used for the same purpose. These shafts ought not to be over 50 feet in length, operated by one set of ropes. Pieces of shafting 15 or 20 feet long can be easily coupled together. The plainest possible construction is sufficient for all practical purposes.

Ribbed glass should be used in these sashes as it prevents the glaring effect of direct and unimpeded sunlight, and diffuses a soft and agreeable light over the whole area to be lighted.

In Fig. 18 is shown a longitudinal section, and in Fig. 19 a cross-section, of this same style of roof, but in this case it is constructed principally of wood instead of steel. The form of the inclined truss, and the method of securing the timbers by bolts is clearly shown. Wall plates of the form shown should be used, as well as proper resting plates on the tops of the central posts, or columns, so constructed as to not only properly support the truss for holding the window frames and sashes, but also to furnish a proper abutment for the lower end of the rafter braces.

The roof timbers should be secured to the walls and to the posts by anchor bolts, to prevent the roof from being lifted by high winds.

In putting on the roof planking for this type of roof different methods

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FIG. 18. - Longitudinal Section of Saw-tooth Roof of Wood Construction.

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FIG. 19. - Transverse Section of Saw-tooth Roof of Wood Construction.

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Fig. 20. — Perspective View of Machine Shop with Saw-tooth Roof.

must be adopted for the steel construction from that used for wood trusses and roof timbers.

In the case of the steel trusses, the supporting bars are shown in solid section in the longitudinal section, Fig. 16, and to these the planks may be secured by bolts, or lag screws, if steel supports are used, or by spikes, if these supports are of wood. In either case the planks will run in the direction of the pitch of the roof.

If the wood construction is used, the rafters will be not over 10 feet centers, and the planks long enough to reach at least two spaces, or twenty feet, and are spiked directly to the rafters, consequently they will run at right angles to them.

The planks should be 3 inches thick and 6 inches wide and be grooved in both edges, and have separate splines put in to connect them.

In case of either steel or wood construction, the roof planks should be covered with good rosin-sized roofing paper, mopped with hot tar, and upon this a heavy quality of roofing tin, or some form of the modern sheet steel roofing.

All sheet metal should be painted on the under side before it is laid. The gutters or

valleys of these roofs should be the subject of careful attention. They need not be of sharp pitch, as a quarter of an inch to the foot will be

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sufficient. Conductor pipes at each valley should carry off the water. In the case of the shop shown in perspective in Fig. 20, the valleys on the high central portion should incline each way from the center and from each side, conductor pipes carrying the water to the valleys in the lower part of the building, and from thence it flows to the conductor pipes at the sides.

Either of the methods above described for constructing the roof will be found economical to build and well adapted to the purposes for which they are to be used.

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