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Plywood
Uses of
Plywood
Plywood
is a sheet good and is one of the most commonly used materials in
woodworking and construction. Plywood comes in many grades and
configurations. It's uses range from sub flooring and roof
sheathing in it's cruder grades, right up to the very finest
cabinets and furniture where numbered and matched sheets are often
used. These sheets are kept in the order the veneer was cut from
the tree, permitting the use of matched panels.
Plywood is relatively inexpensive, has excellent strength and
stability regarding expansion and contraction, and is applicable to
many specialty uses. Plywood is available with almost any spieces
of face veneers, from the most common, to the most exotic woods
available.
As the name suggests, plywood is made up of
multiple sheets, or plies of veneer. This plywood is referred to as
veneer core. These plies are glued together at right angles to each
other, always in odd numbers for stability and balance
of the sheet. A sheet made up of an even number of plies
would be subject to warping and twisting due to the two outer
plies, or face plies having the grain run at ninety degrees to
each other. The amount of plies are determined by the end use
of the sheet. The minimum amount of plies is three and is
used only for thin sheets. Generally, the more plies, the
stronger and more stable the sheet.
Plywood is available with other core
materials. Some plywoods have a softwood lumber for the core,
and is known as lumbercore plywood. It is a high quality product
and is used mainly in cabinets and furniture. It too is a stable
product, and has some advantages over veneer core, particulary in
regards to holding power of the fasteners.
Plywood is graded by the quality of the face
material and uses letters as the identifier. With "A" being the
best and "D" being the worst. Numbers are also used in conjunction
with these letters to help in the ordering process. For example A-1
referres to the face side, or "show side", being as close to
perfect as possible, while the back of the sheet will have a lesser
but still very good quality back. In a typical order
to our wholesaler, we would specify 1 - sheet, 3/4" A-1, V.C.
Maple. This translates into one sheet of 3/4" Maple plywood,
with one "A" grade face, and a veneer core. Had we specified L. C.,
we would have received lumber core plywood.
The glues used in making plywood also vary by the
intended use. Urea-formaldehyde glue is often used for interior
grade plywood, while phenol-formaldehyde glue is common for
exterior uses, including marine grade. Since these glues are
carcinogenic, more and more manufacturers look to use "Greener
Glues".
Certain plywoods do not have alternating plies.
These are designed for a specific purpose. One such plywood is
known as "Bendy Board". This is very flexible and is designed for
making curved parts. This material is available in 1/4, 1/2, 5/8
inch sheets. (or those were the sizes the last time I checked).

The plywood shown in the photos is Bendy Board.
These cylinders are two layers of 3/8 inch material, glued up to
give us the desired 3/4 inch thickness. Using a single layer of 3/4
inch material would have prevented us from making the small radius
required for the project. These parts are used on the bar in the
home page photo, prior to the veneer being added. As you can see,
curves and plywood get along just fie. Keep in mind when ordering,
it is sold in 4 foot by 8 foot sheets, and depending on the
direction you want it to bend determines how you specify your
order. Either 4 feet by 8 feet, or 8 feet by 4 feet.
Other plywoods have more plies and are often used
for cabinet drawers. Baltic Birch is one such plywood. These sheets
were only available in five foot by five foot sheets. I have been
seeing different sizes of late. Another popular plywood for drawers
is called Maple Apple Ply. While this is considerably more
expensive than Baltic Birch, it is much smoother, and when sprayed
with a clear finish, stays much whiter. Spraying Baltic Birch
raises the grain, making it feel rough. It requires some sanding to
knock down the roughness. It also has a tendency to turn amber when
sprayed with most finishes.
There is a plywood made for just about every
purpose imaginable, such as pressure treated, fire retardent,
moisture resistant, marine grade, airplane grade, sign plywood, and
of course hardwood and softwood grade.
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