Understanding the grain of wood is a complex geometric puzzle. Wood comes in many different species and densities which all play heavy roles in the formation of the grain. Just like all living things there are no two exactly the same, only similar.
When planning a new project the species of wood should be given careful thought. The demands of the design will usually favor certain candidates. It is very important to do a little research before ordering any lumber. Also research unfamiliar techniques you will be using during the construction and finishing processes. Remember to test small pieces for workability, both in the machining process, and the finishing process.
You have done your research, purchased your wood, and are ready to begin. By looking at the board through the eyes of a detective you can see some of the stresses or lack of stresses within each piece. Whenever there are knots present you can count on tremendous internal stresses, trying to rip them out will surely make one or both boards go wild. Knots aren't all bad as a matter of fact they possess some of the denser beautiful grain you will find in the board. So consider leaving some of them in your project, it is a Green approach to building, after all knots are a part of wood.
Stress is held with in the board in two ways.
Statically, which tends to minimize its effects over the length of the grain.
Dynamically, which is a loaded response to the external environment the tree grew in. Some trees resist unbelievable forces throughout their lives, and that memory is in the wood, coiled and ready to screw up your project if you are not careful.
Reading grain is part science, detective, and luck. You can think you have seen it all and right in the middle of planing a board an alligator will take a bite out of your masterpiece, or worse yet leave a nasty splinter in your hand. Alligators are caused by stress, and end grain being exposed within the length of the board. Knots are usually the beginning of an alligator but spiral and erratic grain will produce them also. Always perform your work moving towards the end of the open grain and not into it.
Tear out is where parts of the surface during cutting or milling just pull out. Some species are more affected by this than others. If you believe your material to be subject to this than make sure your tools are like new before you begin. All jobs should have properly sharpened tools but some demand it. Not to worry though most of the time the tear out is shallow and can easily be sanded out. Soft woods seem to be more susceptible to than most hardwoods.
There are some species that are inherently brittle, which will add a whole new realm to understanding the wood you are working with. It may have some or all of the traits listed so far and in addition being brittle. When working with these woods special care must be taken at all times to ensure split free assemblies.
Most soft woods share the characteristic of being easily dented. Special care must be taken at all times to minimize dents, especially after sanding. There are a few hardwoods that will possess this trait as well. The best way to test your wood is to simply rub your fingernail across the grain, the result will tell you all you need to know about how to care for the piece.
This by no means is an exhaustive compendium of wood characteristics. My soul motivation in writing this was to enable you to do research, and apply your accumulated knowledge towards years of wood working pleasure. You will be your best teacher, so start the learning curve with optimism.
Wood can be the source of very beautiful creations, and an inspiration to your creative soul. Never take anything for granted when working with wood and you will achieve far better results.
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"There will never be a better day than today to follow your dreams. It is only through living your dream that you can achieve it." William Muncrief 2008
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