"S" or "U" form with sharp bends, which may be clamped or bolted to the work, with or without an adjustable arm to bear against the drill. This flat strap is so adjusted that the drill is over the desired position, when pressure may be exerted on the drill lip by tightening the feed screw.

31. Air and Electric Grinders.-Air grinders (Fig. 70) and electric grinders differ from air or electric drills only in the cutting tool used, which is an abrasive wheel instead of a drill. Electric grinders have an advantage over air grinders in that the speed obtainable is higher, which makes for rapid cutting. In use, the tool is held by the operator and the cutting wheel brought against the work in much the same manner that work is held by an operator and brought against a cutting wheel in the usual stationary shop mounting.

32. Cutting Wheels.-Cutting wheels should be of a grain, hardness, and material suited to the material to be cut. For structural steel, a medium grain, rather hard wheel should be used. For harder steels, a softer wheel of like grain is preferable. Carborundum, alundum, crystolon and like abrasive materials cut faster and better tham emery, or like materials. Micro examination of cuttings shows that the materials first named cut shavings from the steel, while the latter produce globules of molten metal, with proportionate speeds of cutting, endurance of wheels, and requirements for power.

MISCELLANEOUS EQUIPMENT

BY NATHAN C. JOHNSON

33. Air Compressors.-The uses of compressed air in building construction are so varied and cover such a prolonged period extending from placing foundations, as in sinking pneumatic caissons, through steel erection and even to finish painting that the selection of air compressors and the installation of the air distributing system should be planned most carefully.

As the art of producing and using

compressed air is highly developed, a wide choice of compressor equipment is available. Compressors may be driven either by electric motors, steam or gasoline engines, and through belts, gears, or chains as desired and may be obtained to work at any required pressure. Compressors of the smaller sizes are built single stage, all compression taking place. in one cylinder (Fig. 71). The larger sizes are two or three stage, having two or three cylinders, each of which raises the pressure a certain part of the final value. Compressors of from 100 to 300 cu. ft. free air capacity per minute may be mounted for easy portability but solid. foundations are preferable for larger sizes and can generally be made available in modern building construction. To equalize the load on a compressor, as well as to have a constant pressure supply, receivers or storage tanks are used as accumulators in connection with compressors. These must be ample in size and suited to the anticipated demand.

FIG. 71.-Air compressor with receiver, Ingersoll-
Rand Co., N. Y.

Two-stage compressors have been found to give best results when the delivery required of the machine is large. In these, the air is compressed a small amount in the first, or low pressure cylinder, then passes to an intercooler, where, while being held at low pressure, some of the heat due to compression is removed. From the intercooler the air passes to a second cylinder where it is compressed to a higher value and then passed to the receiver.

As air is compressed, its temperature rises causing it to expand a certain amount and exerting a back pressure on the piston. This reduces the efficiency of the machine and is overcome in part by multiple stage compressors and intercooling. Further cooling occurs in the receiver and pipe lines; and as the temperature decreases, the

pressure of the air will also drop. This is loss of energy and the work done by the compressor to balance this loss is likewise lost energy. Such losses, together with friction losses, may amount to 10% or more.

The capacity of a compressor is therefore based on the number of cubic feet of "free air" it will compress per minute to a certain pressure. By "free air" is meant air as found at a pressure of one atmosphere at 60 deg F. From this definition it may readily be seen that the capacity of the same machine will vary according as pressure and temperature conditions are varied.

Data in large volume relative to the size, types, and performance of air compressors, together with data relative to proper size and arrangement of transmission lines have been published. Compressed air engineering is a large art in itself; and comprehensive data are beyond the space limitations of this handbook. Those interested should consult standard text books on the subject as well as the many excellent trade catalogues issued by manufacturers of compressed air equipment.

34. Air Painting Equipment.-Painting by compressed air (Fig. 72) has recently come into quite general use; and is among the newer applications of compressed air to building construction. In this work, air under pressure is fed through a rubber hose, to a metal paint container fitted with a control head (Fig. 73). Air pressure as admitted at the top of the container, forces the paint through a strainer up to the control head and then through a

rubber hose to the "gun." Some of the air entering the control head also is fed direct to the gun. The complete apparatus outside of the compressor therefore consists of the metal container, the gun, and the necessary connecting rubber hose to reach the work.

34a. Metal Container.-The metal container is a tank of 3 to 15-gal. capacity, equipped with the control head which has the necessary valves for adjusting the pressure on the paint and of the air supplied to the gun; a strainer to prevent paint skin, etc., from clogging the line to the gun; and a pressure gage. Containers of the smaller sizes are of riveted steel construction; those of the larger size are of welded construction and have large neck openings to permit of easy cleaning.

346. Guns.-The gun or painting nozzle is shaped like an ordinary pistol, using the trigger to control the supply of paint and air. Its handle carries connections for the air and paint lines. The end of the gun barrel is fitted with a cap and two nose pieces through which is forced the paint and air respectively. Adjustment of the amount of paint is obtained by screwing the cap on or off; and the air supply is regulated by a needle valve under the nose pieces. By proper adjustment of these two, either a conical or fish-tail spray may be obtained. Where desired, the gun may be mounted on a long pole enabling an operator to paint in places where ladders or scaffolding would otherwise be required.

The main advantages claimed over brush painting are: (1) that with pneumatic painting more surface can be covered in less time and with fewer men; (2) that by means of the pole, places otherwise inaccessible can be reached without the aid of ladders or scaffolds; and (3) that by the use of the different caps and nose pieces, light or heavy paints may be used and the type of spray varied. The gun also may be operated at a distance from the container and is not dependent for its effectiveness upon the position of the latter.

The smaller size containers should be used where frequent moving is occasioned as the larger sizes require more than one man to move them. The weight of a 5-gal. unit is about 50 lb. and that of the larger sizes greater in proportion.

Sur

35. Surfacing Machines.-Special machines for finishing the surface of concrete, either in floors or walls, and to remove form marks, may be operated either by air or electricity. faces may also be treated by rubbing by hand with carborundrum; washing with a dilute acid; or brushing with a stiff wire brush. Each of these methods has its place but better and cheaper results can be obtained with a mechanical device.

Air surfaces are machines which are similar to air hammers but strike a much lighter blow. A variety of tools arranged to socket in the device are used for different surface effects. Where it is desired to have a pebbled surface, air surfacers will be found particularly effective, but any desired surface effect can be obtained by a skillful operator and a careful choice of cutting tool.

Electric surfacers (Fig. 74) consist of a motor and a tool using different types of teeth or grinding disks which revolve at high speed and chip or grind the surface to a finish. In one type, the motor is suspended from the operator's shoulders and connected to the tool through a flexible shaft. The weight of the motor for this apparatus is about 30 lb. and that of the tool 10 lb. This machine may be used for simply removing fins and projections, or for obtaining a flat or bush-hammered effect. About 20 sq. ft. of flat finish can be obtained in an hour; and its use is said to reduce the costs over hand methods from 50 to 65%.

36. Stucco and Plastering Machines.-Special machines for applying stucco and plaster have been brought out. It is claimed by the makers that these machines will give a better and more lasting result than will hand methods and that they will reduce costs materially.

Two types are to be had-one which impels the material mechanically against the wire or lath; and the other which places the material by compressed air.

The first type of machine (Fig. 75) consists of a small hopper mounted above a flat bladed propeller driven by an electric motor. The machine weighs about 30 lb. and is fastened to the operator by straps and a coiled

spring to give flexibility, so that the discharge may be directed to any desired place. The stucco material, previously mixed, is fed into the hopper and as it passes through is shot out by the impeller blades through a discharge opening and against the work. From 300 to 400 sq. ft. of surface per hour can be covered to a thickness of 3 in. with such a machine; and due to the high velocity

FIG. 76.-Applying "Gunite" with the cement gun. Container feeding dry sand and cement through flexible hose to nozzle is on ground below scaffolding. Cement Gun Co., Allentown, Pa.

of impact, is said to give a much better surface than where hand methods are employed

The compressed air type, known as the "Cement Gun" (Fig. 76), consists of a drum in which the dry materials are placed after premixing. Air pressure is then applied above, the feed being regulated by a rotating feed wheel within the casing actuated by an air motor and then forced through a hose to the point of application where it is commingled with a fine spray of water delivered through a parallel hose line outside of the casing. While this machine is portable to a certain extent, it is not so much so as the first type due to the necessary auxiliary equipment and it also operates on a different principle. A compressor is necessary with this machine to supply the air to the mixer. The material produced by this device is specified as "Gunite" and has the merit of being very hard and dense.

37. Lighting Equipment for Construction Work. Very often work must be carried on at night, and when such is the case, it becomes necessary to employ artificial light. This may be supplied by electricity, gas, or oil.

Electric light is generally used unless current is not readily available. Where such is the case, gas or oil lights may be substituted. Electric lights will be found to be the most serviceable as they require no attention and with

suitable clusters and reflectors, a large area can be evenly lighted from one place.

The portable carbide light (Fig. 77) is a type of acetylene gas light. Owing to its lightness and large candle power, it is used extensively. The light, however, is a concentrated one and the apparatus requires frequent charging and cleaning. Two types may be obtained, the main difference being that one utilizes calcium carbide in cake form and the other a lump carbide. The apparatus consists of a

water and carbide, 60 lb; has a burning capacity of 12 hr., and costs from 3 to 5ct. an hr. to operate. Small hand units (Fig. 78) may also be obtained for inspection purposes.

Kerosene or gasoline may be used to supply lights for night work and produces a strong fairly white light. The apparatus consists of a special burner and a tank for containing the oil under pressure. Metal tanks of from

10 to 20-gal. capacity are made, and are equipped with a gage and hand pump. The burner consists of a perforated tube nozzle fitted at one end of the tube and connected through a needle valve to the lead pipe of the tank with a shallow tray placed beneath. To use the light, it is necessary to first heat the tube to vaporize the spray. This is accomplished by collecting a small quantity of the fuel on the tray and igniting it. Initial heating only is required as the heat from the light itself is sufficient to heat the tube after once placed in operation. This type of light is cleaner than the carbide light as there is no residue left in the tank, but, as such lights are more expensive to operate, they are not used to as great extent as the carbide lights.

38. Oxy-gas Cutting and Welding Equipment. Not only in wrecking but also wherever steel or iron in any shape has to be cut on the job, an oxy-acetylene or oxy-hydrogen blowpipe or torch is found to be an economical tool. The apparatus in general consists of a blow-pipe or torch, feed piping lines leading from supply to torch, and a generating unit (Fig. 79). The

generating unit, as usually composed, is a tank containing liquified or compressed oxygen, and an acetylene generator or tank where the oxy-acetylene process is used, or tanks of compressed oxygen and hydrogen for the oxy-hydrogen process, together with attached regulating valves.

Oxygen, hydrogen, and acetylene gas, under pressure, are shipped in metal containers and make a fairly portable unit. Due to the fact that acetylene is easily obtainable and gives an extremely high heat, the oxy-acetylene process is the one most used. Especially is this true when welding is to be considered as the electric arc is the only other flame which gives a higher temperature.

The actual cutting by burning or melting the metal is done by an oxygen flame but before this can be undertaken, the material must be preheated, which heating is accomplished by incandescent carbon in the oxy-acetylene flame. The exact procedures followed in cutting vary with the different types of torch, or the gases used, and are determined in large measure by the character of flame produced by the torch tip. Different sizes and types of tips are supplied, each to be used for a specific purpose.

In places where portability is not of much importance, stationary acetylene generators similar to those used for carbide lights may be used. The cost of these generators and their operation is slightly less than when the gas is bought in cylinders, but they require considerable care and attention.

39. Pipe and Bar Threading Machines.-Threading machines both for pipes and bars should be supplied on all jobs of importance. The smaller hand dies and taps form a usual and necessary part of the fitting equipment on smaller work.