Plywood And Curves

Plywood, Lumber-Core Plywood & Laminated Wood | Plywood Hollow Frame | Veneer | Grain Direction In Curved Pieces | Constructing Curves | Special Uses Of Plywood

Plywood, Lumber-Core Plywood, And Laminated Wood

Plywood is produced by placing three, five, seven, or more layers of wood one on top of the other with the grain of each ply at right angles to that of adjacent plies. Each layer is glued to the previous layer and put under heavy pressure. The face veneer generally is in one continuous sheet stripped or peeled from the surface of a single log after the log has been reduced to uniform diameter.

Lumber-core plywood consists of glued strips of solid heartwood covered on each side with a thin panel of plywood. This material has done much to change furniture construction. In addition to plywood and lumber core plywood we have today the possibility of producing different types of panels by using special glues to bond one or more layers of wood with various other materials such as metal and plastic.

Laminated wood is produced by gluing thin sheets of hardwood with the grain running in the same direction. It is used to obtain a solid curvature in the wood. See (B) page 50.

Special Plywood

A—Formation of special panel of 13 layers of wood of same thickness, placed one on top of the other, with adjacent grains perpendicular.

B—Lumber-core plywood with extra thickness.

Plywood Hollow-Frame

Plywood hollow frames are formed with softwood and covered on both sides by plywood panels. This is one way of making up pieces which are not standard sizes. Various types of frames are used in construction of panels, and each has its individual characteristics.

A—Hollow transverse rail frame: This is the simplest type, but permits use of plywood having undulations or deformities. The defects are eliminated by gluing plywood to the perimeter of the frame and making holes in the rails for air circulation.

B—Cross rail frame: This method also permits good construction despite limited deformities in the plywood.

C—Corrugated panel formed by placing cellular cardboard in a frame and gluing it between two sheets of plywood. This type of construction is often used in making flush panel doors.

D—Cross section showing how the plywood should be glued to the frame to reduce irregularities.
 
E—Cross section showing how irregularities occur if the plywood is inadequately supported by braces inside the panel.

Veneer

Veneer is formed by stripping a continuous sheet from the log. This sheet is applied with glue to less expensive woods to create a rich surface effect. The application is made during the process of construction.

A—Veneer must be  applied  across the grain.

B and C—If veneer is applied to only one side of the wood, it will cause the wood to warp. To balance the strain, panels that must be flat should have veneer on both sides.

D—Curved panel made with veneer-covered segment: To prevent the joint lines from showing through it is best to place muslin between the veneer and the wood.

E, F, and G—Three ways to keep curved veneer in place and under pressure until the glue has set. Should the veneer be applied to curved surfaces, a small sack of hot sand should be used to press it tightly to the wood. A veneer must be applied across the grain.

Grain Direction In Curved Pieces
 
Various types of curves and bends appear in furniture design. One finds both internal and external angles. Complete curvature to form cylindrical shapes can be obtained by pressing more than one layer of wood together.

There are many ways of constructing these curves.
 
A and B—Natural wood grain: In (A) the natural direction of the grain is straight, while the grain in (B) is naturally curved.

C through F—Examples of grain direction in curved pieces: Note that the grain runs in the direction it must support. This procedure helps to keep the wood from cracking.

 

Constructing Curves

Round corner with dowel
This system is used for large curves.
 
Round corner frame with block
Where a curve has weakened the joint of two rails, the block provides extra strength.

Round corner edge
The better types of construction employ this method.

Corner block
This method can be used when the panel is to be covered with surfacing material.

Joining two frames with curved corner block
This joint is used in small curved pieces. Constructing Curves
 
Frame joint using curved segments
This method gives maximum stability to a curve.

Steam bending

Curve made to obtain a right-angle bend: This type of right-angle bend (A) can be made successfully with steam in such woods as oak, ash, and walnut, but in other types of wood steam bending is of little use.
 
Laminated wood in curved work

This curve (B), common in commercial production, requires specialized equipment. It is produced by gluing layers of wood with the grain parallel.

Because it is a strong continuous curve, it is often used for chair and table legs.

Curves in lumber core plywood

None of these methods (A through F) should be attempted by the beginning craftsmen. In (A) saw kerfs are made on one side of the solid core, and the core is glued into the frame with two panels of plywood on each side. This makes a good panel. (D) and (E) show two other methods. In (F) two plywood panels are glued together in a form to obtain one panel with desired curvature.

Special Uses Of Plywood

A—Molded plywood
Light molded plywood is obtained by gluing layers of wood together in metal forms. The mold is pressed together with clamps. This method is in wide use in the production of chair seats and backs.
 
Cylinder and cone construction

C—Cone covered with plywood for cabinet work
For upholstery work, cardboard may be substituted for plywood.

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