General

General Notes About Wood | Wood Changes | Seasoning Of Lumber | Selecting And Buying Wood | Cutting And Assembling The Parts | Wood Finish

General Notes About Wood

In order to select the type of wood best suited to the work to be done it is essential to understand the characteristics of the material. I have, therefore, outlined some basic information regarding its structure, as well as methods of sawing and handling.

Structure of wood

Wood is derived from a tree. It is made up of bundles of fibers or long tubes that run parallel to the stem of the tree. These are crossed by other fibers that form the medullary or wood rays. These wood rays pass from the center or pith to the bark and serve to bind the units together. Concentric rings are formed as a layer of wood is added each year. These are called annual rings.A—Partial section of a tree trunk

Note the location of its parts: Medulla, or pith: This is the center of the tree. It is lighter in color and less strong than the heartwood.

Heartwood: This section of the trunk, located between the medulla and the sap-wood, gives us the best building material. Sapwood: The recent annual rings are contained here, between the heartwood and the cambium.

Cambium: This is the most recent annual ring. Bark: This external layer protects the tree.

Sawing the tree into planks

A tree is usually cut during the winter, when there is little sap in the wood. At this time the wood is less subject to fungus attack. After the bark has been stripped, the trunk is washed to prevent fungus, mold, or other growth. This process also helps to season wood.

At the end of the seasoning period the trunk may be sawed into planks in any of a number of different ways. One of the most practical methods is sawing parallel to the grain. This is called plain, or bastard, sawing. Quarter sawing, another method, is used for higher quality work.

Wood Changes

Planks undergo both warping and shrinking during the seasoning process. Shrinking is most noticeable at the outer edges of the plank, because the annual rings of the sap-wood are fresher and less dense. Warping refers to the general change the plank undergoes after being cut.
A—Warping in a plank that includes the pith

B—Warping  and  curvature  of  parallel-sawed (plain-sawed) planks: Note how the curvature runs in a direction opposite to the arc formed by the annual rings.

C—Aligning or joining of two planks must be done on their concave sides.

D—Joining two planks on their convex sides will produce a weak joint.

Seasoning Of Lumber

It is essential that lumber be well seasoned before it is used. The usual methods are as follows:

Natural seasoning: In this method sawed lumber is exposed to free air after it has been carefully stacked.

Water  seasoning:  A  somewhat   quicker method of seasoning consists of immersing the lumber in running water for about one month. The water entering the pores of the wood washes out the sap. The lumber is dried in the open air.

Artificial seasoning: In this method the lumber is placed in a drying kiln, and a current of hot air is allowed to circulate continuously between the layers. For some woods steam may be used. This is the fastest method.

Selecting And Buying Wood

After the design has been selected and studied, the next step is the ordering of material. One method is to buy the lumber in standard lengths and cut the required pieces as listed. Another method is to ask the lumber dealer to cut the material into the sizes you need. There will be a minimum of waste whichever method is used, because standard lumber sizes have been considered in the planning of the designs.

Avoid using solid wood and plywood together in the same piece of furniture, particularly if a flush board is to be visible. If such a combination of materials is unavoidable, glue should never be used for bonding the parts. Plywood and solid wood react differently to drying glue and to atmospheric conditions, but screws or loose joints will permit shrinkage or expansion. However, wood and plywood may be safely combined in edge treatment, as shown on page 52.

Another point to keep in mind is that both soft and hard wood shrink in the process of seasoning. Thus the wood is usually ¾ e in. narrower than the nominal thickness. This difference is of consequence only in fitting such parts as doors, shelves, or drawers. If the wood is of a different thickness from that specified in the design, adjustments must be made in the dimensions of the part to be applied. Therefore it is best to secure lumber of a thickness as close as possible to that specified-
 
Cutting And Assembling The Parts
 
Whether wood is shaped by hand or by use of woodworking machines, the process consists of removing small parts of wood by sawing, planing, or chiseling in accordance with the selected design.

After the design has been studied and suitable wood selected, the various pieces can be traced directly on the wood for cutting. See details, page 8. The parts should be laid out in such a way that the handsomest surfaces of the wood will be seen in the finished piece. In the cutting operation itself, accuracy is very important; if the parts are to fit together as designed, the lumber must be cut at the correct angle. The saw cut should fall outside the pencil line, so that the board can be planed or filed to correct dimensions. (A plane is used on flat surfaces, and a file on curved edges.)

When the parts have been cut and finished to the right sizes, the joints may be marked and executed as indicated in the details. Sometimes it is possible to save time by eliminating the joint and substituting nails. Before any parts are joined, all should be checked to make sure they will fit.

Instructions for assembly are provided with each design. The glue must be spread on both surfaces to be joined, and the pieces clamped together for several hours. Simple clamps or screws and nails may be used to apply pressure. Wood clamps may be made by nailing blocks of wood to the ends of a rail slightly longer than the piece being glued, and applying pressure by inserting wedges between the wood and the blocks.

Large assemblies

Before assembling a large piece of furniture, particularly a built-in unit, it is wise to measure passageways to make sure it can be moved from the shop to the site that has been picked for it. It may be necessary to assemble the piece in two or three units in the shop, and complete the assembly in the room where the piece is to be installed.

Wood Finish

The kind of finish a piece of furniture should receive will depend upon the quality and appearance of the wood, the use it will receive, decorating tastes, and so on. Nothing shows off the beauty of the wood—and the builder's achievement!—quite so well as a "natural" finish. Or it may seem preferable to add a touch of bright color to the decorating scheme of a room by painting the piece. Nowadays furniture makers sometimes achieve bold, striking effects by the carefully planned use of contrasting panels on the same piece: for example, the drawer fronts of a chest might be enameled or lacquered pure white, while the frame could be a strong, deep tone of almost any other color that would "go well" \n the room. A word of caution to the amateur decorator: if you lack confidence in your judgment, or are wavering between color and natural finish, remember that the latter is never in bad taste. Furthermore, a natural finish can later be painted over, if you find you are not happy with it. It is a far more difficult proposition to remove the paint, if you later decide you prefer the "natural" look.

The subject of wood finishing is too extensive to receive adequate treatment here, but a few general pointers are worth giving:

Carefully sand smooth all surfaces, both before and between coats of finish. Grade 2/0 sandpaper is recommended for raw wood; finer grades of waterproof sandpaper— such as 4/0 or 6/0—are suitable between finish coats, and may be dipped in water to prevent clogging and minimize dust. Other methods of smoothing the surfaces, such as rubbing with fine steel wool, pumice, or other fine abrasives, may also be used. Dust should be allowed to settle before liquid finishes are applied, and the air in the workroom should be clear and still. Be sure that a coat of finish is thoroughly dry before sanding and proceeding with the next coat, and never rub or sand the final coat of paint or enamel. Various rubbing compounds or 8/0 sandpaper may be sparingly used after the final coat of shellac or varnish.

Preparation of surface

Most raw woods need careful preparation before they can be painted or finished. Neglect of this essential preliminary will not only increase the number of coats necessary to obtain proper coverage—with consequent waste of materials and labor—but will produce less satisfactory results. Fillers, primers, and undercoats are not cheaper types of finishing material to be used where they won't "show"—they are indispensable components of a proper finish.

In applying finishes, use good brushes and keep them in good condition. It is best to keep special brushes for special uses: one brush for shellac, another for varnish, a third for lacquer. A nylon brush should not be used with shellac, as the alcohol solvent will attack the bristles.

Open-grained hardwoods—such as oak, birch, walnut, mahogany, cherry, elm, hickory, chestnut, or butternut—must be filled. If the wood is to be stained, this operation should precede filling or be combined with it—filler-stain preparations are available in a number of shades. If wood filler is applied separately, it should be brushed or wiped on and the excess rubbed off with a clean rag. It is important to follow the manufacturer's instructions faithfully with all finishing materials.

Close-grained woods—such as maple, pine, fir, gum, cedar, poplar, beech, basswood, or cottonwood—do not need to be filled, but a coat of thin shellac is recommended to seal fir before varnishing, because of the soft grain. If there are any knots or resin pockets in the wood, they should be sealed with shellac or knot-sealer.

Plastic wood or crack filler (in shades to match the wood, if a natural finish is selected) should be used to fill nail holes or crevices after they have been primed, either by the first finish coat or by swabbing with linseed oil or varnish.

Natural finishes

Among natural finishes, the least discoloration of the raw wood is obtained with wax, but this method also offers least protection against hard usage. A single coat of white shellac or clear varnish should precede the wax. Combined varnish-wax preparations are also available.

Clear lacquer can yield striking results, and there are now preparations available which make it possible to apply this traditionally difficult material with a brush instead of a spray-gun.

A "white" shellac finish will discolor wood less than varnish, but is not waterproof. A "5-lb cut" shellac contains 5 lb of shellac gum to the gallon of alcohol; "4-lb cut" contains only 4 lb. Either of these concentrations will give good results, but the "3-lb cut" frequently found in stores is not recommended, except for preliminary coats, which should be thin.

Varnish finish combines durability with the attractiveness of a natural finish. Spar varnish is suitable for pieces like kitchen cabinets, that are exposed to moisture. Other types of varnish are suitable for high-gloss effects, and some types have pigment added to combine the coloring effect of paint with the natural grain of the wood.

Paint Or Enamel Finish

If the wood is to be painted, it must first be primed, although some special formulations and most rubber-base paints are self-priming. If it is to be enameled, best results will be obtained by using an enamel undercoat preparation. It is generally advisable to mix a little of the finish coat into the white primer or enamel undercoat, in order to tint it, and provide a better base for the final pigment. This measure is especially advisable if the final color is very deep.

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