Plywood is a type of manufactured timber made from thin sheets of wood veneer. Size 4'X8'. MR and WBP glue.
Plywood is a type of manufactured timber made from thin sheets of wood veneer. It is one of the most widely used wood products.
Plywood layers (called veneers) are glued together with adjacent plies having their grain at right angles to each other for greater strength. There are usually an odd number of plies so that the sheet is balanced—this reduces warping. Because of the way plywood is bonded (with grains running against one another and with an odd number of composite parts) it is very hard to bend it perpendicular to the grain direction.
Types
Average-quality plywood with 'show veneer'
High-quality concrete pouring plate in plywood
Different varieties of plywood exist for different applications:-
Softwood plywood
Softwood panel is usually made either of cedar, Douglas fir or spruce, pine, and fir (collectively known as spruce-pine-fir or SPF) or redwood and is typically used for construction and industrial purposes.
Hardwood plywood
Used for demanding end uses. Birch plywood is characterised by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel-carrying capacity. Birch plywood has excellent surface hardness, and damage- and wear-resistance.
Decorative plywood (overlaid plywood)
Usually faced with hardwood, including ash, oak, birch, mahogany, Philippine mahogany(often called lauan), and a large number of other hardwoods.
Sizes
The most commonly used thickness range is from 0.6 in.(1.6 mm.) to 3.0 in. (76 mm.). The sizes of the most commonly used plywood sheets are 4 ft.(1.2 m.) wide by 8 ft.(2.4 m.) or 3 ft. (0.9 m.) by 6 ft. (1.8 m.). Width and length may vary in 1 ft.(0.3 m.) in increments.
In US, the most commly used size is: 4 ft by 8 ft or 5 ft by 5 ft. [6]
Grades
Grading rules differ according to the country of origin. Most popular standard is the British Standard (BS) and American Standard (ASTM). Joyce (1970), however, list some general indication of grading rules:
Grade Description
A Face and back veneers practically free from all defects.
A/B Face veneers practically free from all defects. Reverse veneers with only a few small knots or discolorations.
A/BB Face as A but reverse side permitting jointed veneers, large knots, plugs, etc.
B Both side as reverse of A/B
B/BB Face as reverse of A/B. Reverse side as reverse of A/BB
BB Both sides as reverse of B/BB
WG Guaranteed well glued only. All broken knots plugged.
X Knots, knot-holes, cracks, and all other defects permitted.
Commercial Plywood
