METHODS OF FASTENING
A variety of metal fastening devices are used by Seabees in construction. Although nails are the most commonly used fastener, the use of staples to attach wood structural members is growing. For certain operations, screws and bolts are required. In addition, various metal devices exist for anchoring materials into concrete, masonry, and steel.
The increasing use of adhesives (glues and mastics) is an important development in the building industry. Adhesives are used in combination with, or in place of, nails and screws.
Nails, the most common type of metal fasteners, are available in a wide range of types and sizes.
Basic Nail Types
Some basic types are shown in figure 3-75. The common nail is designed for rough framing. The box nail is used for toenailing and light work in frame construction. The casing nail is used in finished carpentry work to fasten doors and window casings and other wood trim. The finishing nail and brad are used for light, wood-trim material and are easy to drive below-the surface of lumber with a nail set.
Figure 3-75.-Basic types of nails.
The size of a nail is measured in a unit known as a penny. Penny is abbreviated with the lowercase letter d. It indicates the length of the nail. A 6d (6-penny) nail is 2-inches long. A 10d (10-penny) nail is 3-inches long (figure 3-76). These measurements apply to common, box, casing, and finish nails only. Brads and small box nails are identified by their actual length and gauge number.
A nail, whatever the type, should be at least three times as long as the thickness of the wood it is intended to hold. Two-thirds of the length of the nail is driven into the other piece of wood for proper anchorage. The other one-third of the length provides the necessary anchorage of the piece being fastened. Protruding nails should be bent over to prevent damage to materials and injury to personnel.
There are a few general rules to be followed in the use of nails in building. Nails should be driven at an angle slightly toward each other to improve their holding power. You should be careful in placing nails to provide the greatest holding power. Nails driven with the grain do not hold as well as nails driven across the grain. A few nails of proper type and size, properly placed and properly driven, will hold better than a great many driven close together. Nails can generally be considered the cheapest and easiest fasteners to be applied.
Figure 3-76.-Nail sizes given in "penny" (d) units.
Figure 3-77 shows a few of the many specialized nails. Some nails are specially coated with zinc, cement, or resin materials. Some have threading for increased holding power of the nails. Nails are made from many materials, such as iron, steel, copper, bronze, aluminum, and stainless steel.
Figure 3-77.-Specialized nails.
Annular and spiral nails are threaded for greater holding power. They are good for fastening paneling or plywood flooring. The drywall nail is used for hanging drywall and has a special coating to prevent rust. Roofing nails are not specified by the penny system; rather, they are referred to by length. They are available in lengths from 3/4 inch to 2 inches and have large heads. The double-headed nail, or duplex-head nail, is used for temporary construction, such as form work or scaffolding. The double head on this nail makes it easy to pull out when forms or scaffolding are torn down. Nails for power nailing come in rolls or clips for easy loading into a nailer. They are coated for easier driving and greater holding power. Table 3-10 gives the general size and type of nails preferable for specific applications.
Staples are available in a wide variety of shapes and sizes, some of which are shown in figure 3-78.
Figure 3-78.-Types of staples.
Heavy-duty staples are used to fasten plywood sheeting and subflooring. Heavy-duty staples are driven by electrically or pneumatically operated tools. Light-duty and medium-duty staples are used for attaching molding and other interior trim. Staples are sometimes driven in by hand-operated tools.
The use of screws, rather than nails, as fasteners may be dictated by a number of factors. These may include the type of material to be fastened, the requirement for greater holding power than can be obtained by the use of nails, the finished appearance desired, and the fact that the number of fasteners that can be used is limited. Using screws, rather than nails, is more expensive in terms of time and money, but it is often necessary to meet requirements for superior results. The main advantages of screws are that they provide more holding power, can be easily tightened to draw the items being fastened securely together, are neater in appearance if properly driven, and can be withdrawn without damaging the material. The common wood screw is usually made of unhardened steel, stainless steel, aluminum, or brass. The steel may be bright finished or blued, or zinc, cadmium, or chrome plated. Wood screws are threaded from a gimlet point for approximately two-thirds of the length of the screw and are provided with a slotted head designed to be driven by an inserted driver. Wood screws, as shown in figure 3-79, are designated according to head style. The most common types are flathead, oval head, and roundhead, as illustrated in that order in figure 3-79, All of these screws can have slotted or Phillips heads.
Figure 3-79.-Types of screws.
Table 3-10.-Size, Type, and Use of Nails
To prepare wood for receiving the screws, bore a body hole the diameter of the screw to be used in the piece of wood that is to be fastened (figure 3-80). You should then bore a starter hole in the base wood with a diameter less than that of the screw threads and a depth of one-half or two-thirds the length of the threads to be anchored. The purpose of this careful preparation is to assure accuracy in the placement of the screws, to reduce the possibility of splitting the wood, and to reduce the time and effort required to drive the screw. Properly set slotted and Phillips flathead and oval head screws are countersunk sufficiently to permit a covering material to be used to cover the head. Slotted roundhead and Phillips roundhead screws are not countersunk, but they are driven so that the head is firmly flush with the surface of the wood. The slot of the roundhead screw is left parallel with the grain of the wood.
The proper name for a lag screw (shown in figure 3-79) is lag bolt or wood screw. These screws are often required in constructing large projects, such as a building. They are longer and much heavier than the common wood screw and have coarser threads that extend from a cone, or gimlet point, slightly more than half the length of the screw. Square-head and hexagonal-head lag screws are always externally driven, usually by means of a wrench. They are used when ordinary wood screws would be too short or too light and spikes would not be strong enough. Sizes of lag screws are shown in table 3-11. Combined with expansion anchors, they are used to frame timbers to existing masonry.
Figure 3-80.-Proper way to sink a screw.
Expansion shields, or expansion anchors as they are sometimes called, are used for inserting a predrilled hole, usually in masonry, to provide a gripping base or anchor for a screw, bolt, or nail intended to fasten an item to the surface in which the hole was bored. The shield can be obtained separately, or it may include the screw, bolt, or nail. After the expansion shield is inserted in the predrilled hole, the fastener is driven into the hole in the shield, expanding the shield and wedging it firmly against the surface of the hole.
For the assembly of metal parts, sheet metal screws are used. These screws are made regularly in steel and brass with four types of heads: flat, round, oval, and fillister, as shown in that order in figure 3-79.
Table 3-11.-Lag Screw Sizes
Wood screws come in sizes that vary from 1/4 inch to 6 inches. Screws up to 1-inch in length increase by eighths, screws from 1 to 3 inches increase by quarters, and screws from 3 to 6 inches increase by half inches. Screws vary in length and size of shaft. Each length is made in a number of shaft sizes specified by an arbitrary number that represents no particular measurement but indicates relative differences in the diameter of the screws. Proper nomenclature of a screw, as shown in figure 3-81, includes the type, material, finish, length, and screw size number, which indicates the wire gauge of the body, drill or bit size for the body hole, and drill or bit size for the starter hole. Tables 3-12 and 3-13 provide size, length, gauge, and applicable drill and auger bit sizes for screws. Table 3-11 gives lengths and diameters of lag screws.
Bolts are used in construction when great strength is required or when the work under construction must be frequently disassembled. Their use usually implies the use of nuts for fastening and, sometimes, the use of washers to protect the surface of the material they are used to fasten. Bolts are selected for application to specific requirements in terms of length, diameter, threads, style of head, and type. Proper selection of head style and type of bolt results in good appearance as well as good construction. The use of washers between the nut and a wood surface or between both the nut and the head and their opposing surfaces helps you avoid marring the surfaces and permits additional torque in tightening.
Carriage bolts fall into three categories: square neck finned neck and ribbed neck (figure 3-82). These bolts have round heads that are not designed to be driven. They are threaded only part of the way up the shaft. Usually, the threads are two to four times the diameter of the bolt in length. In each type of carriage bolt, the upper part of the shank, immediately below the head, is designed to grip the material in which the bolt is inserted and keep the bolt from turning when a nut is tightened down on it or removed. The finned type is designed with two or more fins extending from the head to the shank. The ribbed type is designed with longitudinal ribs, splines, or serrations on all or part of a shoulder located immediately beneath the head. Holes bored to receive carriage bolts are bored to be a tight fit for the body of the bolt and counterbored to permit the head of the bolt to fit flush with, or below the surface of, the material being fastened. The bolt is then driven through the hole with a hammer. Carriage bolts are chiefly for wood-to-wood application, but they can also be used for wood-to-metal applications. If used for wood-to-metal application, the head should be fitted to the wood item. Metal surfaces are sometimes predrilled and countersunk to permit the use of carriage bolts metal to metal. Carriage bolts can be obtained from 1/4 inch to 1 inch in diameter and from 3/4 inch to 20 inches long (table 3-14). A common flat washer should be used with carriage bolts between the nut and the surface.
Table 3-12.-Screw Sizes and Dimensions
Table 3-13.-Drill and Auger Bit Sizes for Wood Screws
Table 3-14.-Carriage Bolt Sizes
Machine bolts (figure 3-82) are made with cut national fine and national coarse threads extending in length from twice the diameter of the bolt plus 1/4 inch (for bolts less than 6 inches in length) to twice the diameter of the bolt plus 1/2 inch (for bolts over 6 inches in length). They are precision made and generally applied metal to metal where close tolerance is desirable. The head may be square, hexagonal, rounded, or flat countersunk. The nut usually corresponds in shape to the head of the bolt with which it is used. Machine bolts are externally driven only. Selection of the proper machine bolt is made on the basis of head style, length, diameter, number of threads per inch, and coarseness of thread. The hole through which the bolt is to pass is bored to the same diameter as the bolt. Machine bolts are made in diameters from 1/4 inch to 3 inches and may be obtained in any length desired (table 3- 15).
Table 3-15.-Machine Bolt Sizes
Stove bolts (figure 3-82) are less precisely made than machine bolts. They are made with either flat or round slotted heads and may have threads extending over the full length of the body, over part of the body, or over most of the body. They are generally used with square nuts and applied metal to metal, wood to wood, or wood to metal. If flatheaded, they are countersunk. If roundheaded, they are drawn flush to the surface.
An expansion bolt (figure 3-82)is a bolt used in conjunction with an expansion shield to provide anchorage in substances in which a threaded fastener alone is useless. The shield, or expansion anchor, is inserted in a predrilled hole and expands when the bolt is driven into it. It becomes wedged firmly in the hole, providing a secure base for the grip of the fastener.
A toggle bolt (figure 3-82)is a machine screw with a spring-action, wing-head nut that folds back as the entire assembly is pushed through a prepared hole in a hollow wall. The wing head then springs open inside the wall cavity. As the screw is tightened, the wing head is drawn against the inside surface of the finished wall material. Spring-action, wing-head toggle bolts are available in a variety of machine screw combinations. Common sizes range from 1/8 inch to 3/8 inch in diameter and 2 inches to 6 inches in length. They are particularly useful with sheetrock wall surfaces.
The molly bolt or molly expansion anchor (figure 3-82) is used to fasten small cabinets, towel bars, drapery hangers, mirrors, electrical fixtures, and other lightweight items to hollow walls. It is inserted in a prepared hole. Prongs on the outside of the shield grip the wall surfaces to prevent the shield from turning as the anchor screw is being driven. As the screw is tightened, the shield spreads and flattens against the interior of the wall. Various sizes of screw anchors can be used in hollow walls 1/8 inch to 1 3/4 inches thick.
Driftpins are long, heavy, threadless bolts used to hold heavy pieces of timber together (figure 3-83). They have heads that vary in diameter from 1/2 to 1 inch and in length from 18 to 26 inches. The term "driftpin" is almost universally used in practice. However, for supply purposes, the correct designation is driftbolt.
Figure 3-83.-Driftpin (driftbolt).
To use the driftpin, you make a hole slightly smaller than the diameter of the pin in the timber. The pin is driven into the hole and is held in place by the compression action of the wood fibers.
The corrugated fastener is one of the many means by which joints and splices are fastened in small timber and boards. It is used particularly in the miter joint. Corrugated fasteners are made of 18- to 22-gauge sheet metal with alternate ridges and grooves; the ridges vary from 3/16 to 5/ 16 inch, center to center. One end is cut square; the other end is sharpened with beveled edges. There are two types of corrugated fasteners: one with the ridges running parallel (figure 3-84, view A); the other with ridges running at a slight angle to one another (figure 3-84, view B), The latter type has a tendency to compress the material since the ridges and grooves are closer at the top than at the bottom. These fasteners are made in several different lengths and widths. The width varies from 5/8 to 1 1/8 inches; the length varies from 1/4 to 3/4 inch. The fasteners also are made with different numbers of ridges, ranging from three to six ridges per fastener. Corrugated fasteners are used in a number of waysto fasten parallel boards together, as in fastening tabletops; to make any type of joint; and as a substitute for nails where nails may split the timber. In small timber, corrugated fasteners have greater holding power than nails. The proper method of using the fasteners is shown in figure 3-84.
Figure 3-84.-Corrugated fasteners and their uses.
Builders use many different types of adhesives in various phases of their construction projects. Glues (which have a plastic base) and mastics (which have an asphalt, rubber, or resin base) are the two major categories of adhesives.
The method of applying adhesives, their drying time, and their bonding characteristics vary. Some adhesives are more resistant to moisture and to hot and cold temperatures than others.
The primary function of glue is to hold together joints in mill and cabinet work. Most modern glues have a plastic base. Glues are sold as a powder to which water must be added or in liquid form. Many types of glue are available under brand names. A brief description of some of the more popular types of glue is listed below.
Polyvinyl resin, or white glue, is a liquid that comes in ready-to-use plastic squeeze bottles. It does a good job of bonding wood together, and it sets up (dries) quickly after being applied. Because white glue is not waterproof, it should not be used on work that will be subjected to constant moisture or high humidity.
Urea resin is a plastic based glue that is sold in a powder form. The required amount is mixed with water when the glue is needed. Urea resin makes an excellent bond for wood and has fair water resistance.
Phenolic resin glue is highly resistant to temperature extremes and water. It is often used for bonding the veneer layers of exterior grade plywood.
Resorcinol glue has excellent water resistance and temperature resistance, and it makes a very strong bond. Resorcinol resin is often used for bonding the wood layers of laminated timbers.
Contact cement is used to bond plastic laminates to wood surfaces. This glue has a neoprene rubber base. Because contact cement bonds very rapidly, it is useful for joining parts that cannot be clamped together.
Mastics are widely used throughout the construction industry. The asphalt, rubber, or resin base of mastics gives them a thicker consistency. Mastics are sold in cans, tubes, or canisters that fit into hand-operated or air-operated caulking guns.
These adhesives can be used to bond materials directly to masonry or concrete walls. If furring strips are required on a wavy concrete wall, the strips can be applied with mastic rather than by the more difficult procedure of driving in concrete nails. You can also fasten insulation materials to masonry and concrete walls with a mastic adhesive. Mastics can also be used to bond drywall (gypsum board) directly to wall studs. They can also be used to bond gypsum board to furring strips or directly to concrete or masonry walls. Because you dont use nails, there are no nail indentations to fill.
By using mastic adhesives, you can apply paneling with very few or no nails at all. Wall panels can be bonded to studs, furring strips, or directly against concrete or masonry walls. Mastic adhesives can be used with nails or staples to fasten plywood panels to floor joists. The mastic adhesive helps eliminate squeaks, bounce, and nail popping. It also increases the stiffness and strength of the floor unit.