More about lumber

This page was created out of our own interest in trees and lumber and a need to know more about the working properties of wood. We hope you will find the information below helpful. If you would like to contribute to the information below please feel free to send in your contribution. We are always interested in learning something new and sharing it with other internet users.

Tree growth

When trees grow they expand their trunks by addition new peripheral rings layers. if you look at the end of a cut log you can see a series of concentric rings. These growth rings each represent one year of growth. each ring may have two parts, a lighter part (early wood) that represents the fast growth that happens during the early season, and the darker part that represents the slower growth (late wood) that occurs during the late season. environmental and climatic conditions will effect the amount of growth each season and thus the size of each part of a each ring. large ring show a favorable growing years small ring show less favorable growth conditions. tropical and sub tropical trees which are exposed to favorable growth conditions year round may not show growth rings at all.

The image below shows a section view of a growth ring and 100x. the early wood is the area with thin walls and large cell cavities. the late wood is the area with the thicker cell wall and smaller cell cavity. since the  late wood is  slow growing with thick cell walls it is more dense then early wood. in general it can be said that slower growing trees will have stronger or more dense wood then fast growing trees

Milling timber

When a log is cut into boards a variety of sawing pattern are used. different saw patterns produces boards with different grain patterns relative to the boards surface. the grain pattern in lumber refers to the way that the  growth rings are represented relative to the boards face or surface. If a board is cut so that the growth rings are tangential with the boards face it is called flat sawn. (the annual rings form angles of 45 to 90 degrees with the surface of the piece.)  This produces  less expensive quality lumber. when a board is cut so that the growth rings are radial to the surface (the annual rings form angles of 45 to 90 degrees with the surface of the piece.) it is called quarter sawn and produces a higher quality lumber

Their are basic several patterns used to render boards from a log, plain sawn, quarter sawn. and , rift sawn patterns

Plain sawn boards are produced by cutting tangentially to a tree’s growth rings. this pattern creates the fewest quarter sawn boards but rather creates the familiar "flame shaped" pattern.  This method also the most cost effective thus produces the most lumber and least waist from each log.

Plain sawn lumber  expands and contract more than quarter sawn board but, works well when properly dried and acclimated to the job site before use.

Quarter sawing means cutting a log radially (at a 90-degree angle) to the growth rings to produce a vertical grain pattern . This pattern produces fewer and narrower boards per log than plain sawing.  however the quality of each board is much better.  Quarter-sawn boards will expand and contract less than boards sawn by other methods. quarter sawn logs require a lot of processing and produces lots of quarter sawn boards of various grades. their is also little waist in the is process

 Rift sawing at a 30-degree or greater angle to the growth rings produces narrow boards with accentuated vertical grain pattern. Rift-sawn boards are often favored for fine furniture and other applications where matching grain is important. This type of lumber is available in limited Quantities and species and as can be seen produces more wasted material per log.

 To summarize if the growth rings are at and angle of 0° to 45°  relative to the face of the board,  the board is flat sawn and, if the growth rings are 45° to 90° the board is quarter sawn. Quarter-sawn boards are less likely to distort or crack during the drying process and are more stable in service.

Lumber movement

Wood shrinks and expands over time as its moisture content changes. this can be seen in your house when it rains a lot some wooden doors may stick a bit. that is because the wood has expanded. this can be come an issue when using wood near water like in boats and paddles. this can be a compounded concern when laminating two types of wood. this is because different wood species have different expansion rates. if that's not enough to think about expansion rates are different with in species based on the direction of the expansion relative the  grain orientation. the two directions of expansion are called radial and tangential movement . the two directions of movement are illustrated in the image below.

Shrinkage

 Volumetric shrinkage is a term used to answer the question "how stable is this wood". values shown describe the shrinkage of the wood from green to oven dry. since this is a measure of volume both tangential and radial movement are considered in this measure. This is a good number for comparing overall values between species.

Working Load

working load- under construction

Shear Stress

Shear stress- under construction

source data for graphs

Source data for this page came from: United States Forestry Service

For more information about Wood properties and uses visit USFS. forest product research labs wood hand book

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