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 Plywood

 

Uses for 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).

  Cylinder made from Bendy Board  Edge View of Bendy Board

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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