Draw Manga. Tom Carpenter

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      Choosing the right plywood for your woodworking project is an important task. In addition to the various core, thickness and face veneer options, you’ll also need to make a decision on the plywood grade. Basically, there are two grading systems in use today. The one most people are familiar with is administered by the APA (Engineered Wood Association, formerly the American Plywood Association). The APA grade stamps (See Illustration, next page) are found on sanded plywood, sheathing and structural (called performance-rated) panels. Along with grading each face of the plywood by letter (A to D) or purpose, the APA performance-rated stamp lists other information such as exposure rating, maximum allowable span, type of wood used to make the plies and the identification number of the mill where the panel was manufactured. Many hardwood-veneer sanded plywood panels are graded by the Hardwood Plywood and Veneer Association (HPVA). The HPVA grading numbers are similar to those employed by APA: they refer to a face grade (from A to E) and a back grade (from 1 to 4). Thus, a sheet of plywood that has a premium face (A) and a so-so back (3) would be referred to as A-3 by HPVA (and AC by APA).

       NOTICE

      Particleboard and MDF usually contain urea formaldehyde resins that continue to emit low levels of formaldehyde gas for at least six months as they cure. People with high sensitivity to chemical vapors should limit the number of composite panels added to a room at one time. Always wear a particle mask or respirator as required and provide adequate dust collection and ventilation when cutting or shaping these products.

Particleboard: Particleboard possesses several unique qualities that might make it a good choice for your next built-in project— particularly if the project includes a counter or tabletop. Particleboard is very dimensionally stable (it isn’t likely to expand, contract or warp); it has a relatively smooth surface that provides a suitable substrate for laminate; it comes in a very wide range of thicknesses and panel dimensions; and it is inexpensive. But particleboard does have some drawbacks: it lacks stiffness and shear strength; it has poor screw-holding ability; it degrades when exposed to moisture; it’s too coarse in the core to be shaped effectively; and it’s heavy.

      Medium-density fiberboard (MDF): MDF is similar to particleboard in constitution, but is denser and heavier. The smoothness and density of MDF make it a good substrate choice for veneered projects; the rougher surface of particleboard and most plywoods do not bond as cleanly with thin wood veneer. You can even laminate layers of MDF to create structural components that can be veneered or painted. MDF is also increasing in popularity as a trim molding material.

      Melamine board: Melamine is fashioned with a particleboard core with one or two plastic laminate faces. Thicknesses range from ¼ to ¾ in. Stock colors at most lumber yards and building centers generally are limited to white, gray, almond and sometimes black. The panels are oversized by 1 in. (a 4 x 8 sheet is actually 49 x 97 in.) because the brittle melamine has a tendency to chip at the edges during transport. Plan to trim fresh edges.

      Every sheet of plywood is stamped with grading information. On lower-grade panels, such as exterior sheathing, the stamp can be found in multiple locations on both faces. Panels with one better-grade face are stamped only on the back, and panels with two better-grade faces are stamped on the edges.

       Face grade descriptions

N	Smooth surface “natural finish” veneer. Select, all heartwood or all sapwood. Free of open defects. Allows not more than six repairs, wood only, per 4 x 8 panel, made parallel to grain and well-matched for grain and color.
A	Smooth, paintable. Not more than 18 neatly made repairs, boat, sled or router type, and parallel to grain, permitted. May be used for natural finish in less demanding applications. Synthetic repairs permitted.
B	Solid surface. Shims, circular repair plugs and tight knots to 1 in. across grain permitted. Some minor splits permitted. Synthetic repairs permitted.
C plugged	Improved C veneer with splits limited to ⅛-in. width and knotholes and borer holes limited to ¼ x ½ in. Admits some broken grain. Synthetic repairs permitted.
C	Tight knots to 1½ in. Knotholes to 1 in. across grain and some 1½ in. if total width of knots and knotholes is within specified limits. Synthetic or wood repairs. Discoloration and sanding defects that do not impair strength permitted. Limited splits allowed. Stitching permitted.
D	Knots and knotholes to 2½ in. across grain and ½ in. larger within specified limits. Limited splits are permitted. Stitching permitted. Limited to Interior and Exposure 1 or 2 panels.

       Source: Engineered Wood Association

       Plywood veneer grain patterns

       Rotary cut

       Sliced (plain-sawn)

       Sliced (quarter-sawn)

COMMON HARDWOODS

       A. RED OAK

      Uses: Indoor furniture, trim, flooring, plywood and veneers

      Sources: United States and Canada

      Characteristics: Straight, wide grain pattern with larger pores. Tan to reddish pink in color. Quartersawing reveals narrow medullary rays.

      Workability: Machines easily with sharp steel or carbide blades and bits. Not prone to burning when machined. Drill pilot holes first for nails or screws.

      Finishing: Takes stains and clear finishes well, but pores will show through if painted unless they are filled

      Price: Moderate

       B. WHITE OAK

      Uses: Indoor and outdoor furniture, trim, flooring, plywood and veneers

      Sources: United States and Canada

      Characteristics: Straight, wide grain pattern, tan with yellow to cream tints. Quartersawing reveals wide medullary rays. Naturally resistant to deterioration from UV sunlight, insects and moisture.

      Workability: Machines easily with sharp steel or carbide blades and bits. Not prone to burning when machined. Drill pilot holes first for nails or screws.

      Finishing: Takes stains and clear finishes like red oak, but narrower pores reduce the need for filling

      Price: Moderate to expensive

       C. HARD MAPLE

      Uses: Indoor furniture, trim, flooring, butcher block countertops, instruments, plywoods and veneers

      Sources: СКАЧАТЬ