Sheet Materials

There are various benefits to using sheet materials: they are generally more stable than solid timber, thickness tends to be uniform, and quality is fairly consistent if bought from the same supplier. Veneered boards enable you to utilize natural timbers — sometimes with quartersawn or exotic figuring ­reasonably economically. There is also less impact on the environment than when using certain solid timbers. Plastic coatings are widely used on sheet materials used for kitchen manufacture and other mass-produced furniture.

Medium Density Fibreboard

Medium-density fibreboard (MDF) consists of minute particles of wood mixed with a heavy-duty resin. It is the most versatile man-made board of all, used extensively for furniture-making, toys and shop fit-outs, as well as joinery and carpentry projects. More stable than other boards, it is also relatively cheap. It comes in wide range of thicknesses from 2 mm (3/32 in) up to 51 mm (2 in) and a variety of surface finishes. An excellent surface for veneering, painting, staining or polishing, the edge can be shaped and spindle-moulded like solid timber. It can be routed easily to provide unique 3D textured surfaces, although the router should be hooked up to a dust extractor. Moisture-resistant (MR) and fire-resistant (FR) grades are available, while melamine-faced MDF is used extensively for building kitchen units and office furniture. Edges of veneered MDF boards are commonly finished with hardwood lippings that match the veneer. Increasingly, MDF is replacing softwood in the construction industry for joinery items such as skirting and door architraves.

Contemporary designers and furniture-makers can now benefit from coloured MDF. The colours are created using organic dyes mixed with the wood fibres before the boards are pressed. They can be machined in the same way as normal MDF and the colour is consistent throughout the board thickness. Only a clear finish is needed to seal the surface.

TIPS

  • Before sawing a veneered board, score the underside of the cutting line with a craft knife and straightedge, or stick masking tape along the line. Either method prevents the veneer from splintering. Man-made boards, MDF and chipboard in particular, require very sharp saws for cutting. High resin content will blunt saw teeth and planing edges at twice the rate of real wood.
  • It is essential to wear a good dust mask when machining these materials, especially MDF, as breathing in the fine dust is harmful.

Plywood

Originally the most widely used board, plywood is now somewhat overshadowed by MDF. It consists of a number of layers of constructional veneers, each laminated together to the previous layer with the grain at 90 degrees. Generally, the more layers of veneer the more stable the board. Outer leaves may be hardwood or softwood. Much plywood today is made from veneer leaves that have been poorly dried and result in distorted boards, which means you may have to search for undistorted boards.

There are several grades of plywood, varying enormously in quality and cost. The cheapest is ‘shuttering ply’, used extensively in the construction industry for building formwork for concreting and other temporary structures. A release agent is first applied to the plywood’s surface to prevent the concrete sticking as it cures. ‘Birch ply’ is regarded as the best quality for both internal and external use, while ‘marine ply’ is water-resistant and used widely for boat building. This is commonly made from Douglas fir or larch.

Thickness ranges from model-makers’ aero ply’ at 1 mm, up to 25 mm (approximately 1/32 -1 in). A more recent development is moisture-resistant flexible plywood, which enables instant curves to be formed easily in furniture and joinery projects. Thickness ranges up to 8 mm (5/16 in). Flexible MDF has almost identical properties to this plywood and is available in similar thicknesses. Fire-retardant plywood is used widely in the construction industry.

Blockboard

Blockboard consists of an inner core of softwood strips ­about 22 mm (7/8 in) wide — veneered over at right angles to the grain in a rotary-cut veneer, such as gaboon. Good-quality blockboard is not always easy to find: the inner softwood core is often not dried thoroughly. When it eventually does dry, a pattern showing the core strips is revealed through the polished surface, sometimes referred to as ‘telegraphing’. On poorer quality blockboard the softwood strips of the inner core do not always butt up tightly against each other. This may not be apparent until you saw through the board when gaps can appear. Veneered blockboard is often used for carcases and cabinets, as well as internal joinery, shop fitting and screens.

Laminboard is a higher quality blockboard, but is rarely used nowadays because of its cost. The inner core strips are about 6 mm (¼ in) wide, creating a more stable material than blockboard.

Chipboard

Also known as particle board, chipboard comes in several grades. It consists of wood chips mixed with synthetic resin, which are placed in a heated press. Different layers in the thickness are visible. For smooth-surface chipboards, finer particles of chip are compressed on the outer faces with a coarser, looser wood chip used for the middle. A favourite with the construction industry, chipboard is also used extensively for shelving and lower grade furniture. Some variants are made for exterior use, while others are specifically designed for kitchen worktops — up to 51 mm (2 in) thick. Decorative chipboards are available with resin, paper-coated, plastic or wood-veneered surfaces.

Chipboard has little strength unsupported, and tends to sag under its own weight. Various types of edge lipping are available in plastic, metal and wood. Many require either a sawn or routed groove for attachment, or are glued with cramps. A chipboard edge without protection is not only unsightly, but leaves the edge vulnerable to chipping.

Flooring-grade chipboard is tongued and grooved on all four edges, although it can also be square-edged. A tongue simply locates into a matching groove, adding to the overall strength and preventing sagging when stepped on. Where panels are sawn to length or width, the resulting butt joints should be positioned over a joist or have a supporting batten nailed underneath. Narrow boards are useful for flooring in attics, as they are designed to pass through a ceiling hatch easily.

Hardboard

Hardboard is a fibreboard, similar to MDF, consisting of tiny wood particles mixed with a resin. Sugar-cane pulp is also traditionally used in its manufacture. Hardboard is often laid on uneven flooring before laminate wood or carpet is laid. Perforated hardboard, or pegboard, is useful for tool storage panels. Special hooks are simply inserted into the holes. Oil-tempered hardboard is impregnated with resins and oils, making it weather resistant. Hardboard comes in thicknesses from 2-6 mm (approximately 3/32 – 1/4 in) and is available in a limited range of colours as well as the more common original brown finish.

Hardboard should be conditioned before being nailed rigidly to a framework; if not, it will buckle after fixing. A sheet should be laid down and water brushed or sprayed on the back. This ensures that the sheet expands and will pull tightly when dry. Allow to dry before nailing in place.

Veneered boards

There was a time when you could buy plywood and blockboard veneered on both sides with pine or a hardwood such as oak. Now, however, this option only really exists with MDF. For interior use, the thinnest boards may have a decorative veneer on just one side, with an inferior balancing veneer on the reverse. Above 6 mm (¼ in), boards may have a quartersawn veneer on one side, with crown-cut veneer on the reverse. Typical veneers are ash, white and steamed beech, sapele, cherry, maple, oak, birch, American black walnut and pine. A stable material for making furniture, these boards should be cut very carefully to prevent the veneer breaking out underneath. Thickness ranges from 4-26 mm (1/8 – 1 1/32 in), with panels reaching 3,050 mm (10 ft) in length.

Working with sheet materials

Sheet materials are best cut with a circular saw fitted with a fine-tooth TCT blade. At least 40 teeth are recommended for sawing veneered boards. If using a portable saw, run the tool against a straight guide batten cramped across the board, checking for alignment with a large try square. Always use dust extraction when sawing any man-made material.

Where you see defects in a board’s face, try not to use fillers. These shrink in time and show below the surface. Always use the actual veneer material — birch for birch ply, gaboon for gaboon ply and MDF for repairs to MDF, and so on.

Although small-section, solid-wood lippings can simply be glued to the edges of sawn boards without problems, do not rely on doing this for heavy lippings. Rout a groove in both the back of lipping and the board edge for a loose tongue of plywood or solid timber. This should be a snug fit and will increase the strength of the gluing surface.

When planing solid-wood lippings level with the surface of a veneered board, be careful not to break through the face. The same applies to ordinary chipboard, where planing too deep will reveal a coarser chipboard which is very noticeable under a coat of paint.

Hardware and fasteners have been developed specifically for jointing sheet materials and assembling carcases built from them. These include everything from simple plastic corner blocks and chipboard screws to sophisticated concealed hinges and dowel connector systems. For most hardware, holes should be bored precisely at 90 degrees for professional results. Use a pillar drill or stand-mounted power tool for this.

SHEET SIZES

Most sheet materials conform to a standard size of 2,440 x 1,220 mm (8 x 4 ft). Some MDF boards are produced in lengths of 3,050 mm (10 ft), with widths of 1,200 mm or 1,525 mm (4 or 5 ft). Melamine-faced MDF can be purchased up to 3,660 mm (12 ft) in length, and widths of up to 2,050 mm (approximately 81 in). These industrial-sized boards are really only suitable for converting on a vertical wall saw before final dimensioning on a panel saw.

Word Discription :

Fillers Substances used to fill small holes and defects in timber. Usually chemicals, although sawdust mixed with glue is sometimes used. Melamine A durable, hard plastic coating applied to sheet materials during manufacture. Quartersawn Planks cut from a tree radially, where the growth rings are at least 45 degrees to the face. This technique exposes the best figure and timber is most stable.

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