9-12

AN EXERCISE IN THINKING

 

by Grandpa Cliff

 

Oct 20, 2005

 

 

We see wood everyday, and we see the patterns and grain in it.  This angel is wondering why wood has so many interesting patterns.  Scientists are also curious about a lot of things.  If you are curious, you should enjoy this thinking exercise.  

 

It is not important for you to learn the facts on this page, but if you learn the general ideas you will better understand and enjoy looking at wood patterns in furniture, wall paneling, wooden bowls, etc.  This webpage is an exercise of your mind.  Sometimes it is important to learn things, and sometimes it is important just to use your mind trying to picture something that is written.  The exercise of your mind today will help you figure out more complicated things later.  So, let's start exercising.

 

SAWING A LOG

There are two main ways to cut boards from a log.  The boards can be:

1)  Plain sawn

2)  Quarter sawn

 

            

In these two boards, you are looking at the small end of the board.  The difference in the pattern at the end of the board is due to the way the saw cut through the annual rings of the log.  The whole board is made of wood, either sapwood, heartwood, or both.  The lines are the Summer Wood of annual rings.  Between the lines is the Spring Wood that has larger cells.  

 

PLAIN SAWN LUMBER

 

Look at the top of the Plain Sawn diagram.  The top annual ring touches the face of the board in two places.  Let's say that the board was cut from the heartwood, but that the layer above the board was sapwood.  

Then, the edges of the face would show just a little of the sapwood.  The face would look like this Redwood board.  

 

 

 

 

 

 

The log to the right has been plain sawn.  This type of sawing wastes the least wood.  When the bark is sawn off each side, just a little sapwood will be attached to it.  As you can tell, the log has been sawn into very thick pieces, much thicker than the average board.  

 

 

Plain sawn cuts also take the least amount of time of the various kinds of cuts that could be made.  Saving wood and saving time means that the mill will make more money, or can charge less for the wood that they sell.

 

 

 

 

  Plain sawn Oak wood shows an interesting pattern to the annual rings.  The

  dark lines are the dark lines of annual rings.  The angle of the cut makes 

  them wider than expected.  When looking at furniture made with this kind of

  cut, your eye is drawn to the pattern instead of the workmanship of the

  furniture.  Furniture makers want you to look at the furniture they made, so

  they prefer the quarter sawn grain.  Also, the quarter sawn wood is less likely

 to warp, crack, bow, or change its shape.  

  

QUARTER SAWN LUMBER 

 

The term quarter sawn refers to the fact that the boards are cut from a quarter of a log instead of a whole log.  To get a quarter log, a whole log is first cut in half along its length.  Then, each half is cut in half again.  The log has then been cut into four quarters.  Each quarter is then sawed as in the following diagram.  In the cuts below, the saw blade remains vertical at all times, so the log has to be rotated (turned) 90o after every cut.  This extra amount of time causes quarter sawn lumber to be more expensive.  However, it is better lumber.  

 

 

    

 

 

 

 

 

   The next diagrams show what happens to the wood in each step.  

 

 

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1. Cut board.  Remove board. Rotate log 90o counter-clockwise; cut board

Remove board Rotate log 90o clockwise; cut board   Keep repeating till all boards are cut.

 

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Now that you know the procedure, go back to the diagram numbered 1-8.  Try to picture which way the quarter log is turned each time and which side the board is cut from.  This is a good mental exercise.  If you can't do it, start reading again from just below the dark blue print above.  If you still can't do it, come back and try again another day.

 

The advantage of quarter sawn lumber is that the annual rings go almost straight from one face of the board to the other (the annual rings are almost perpendicular to the face of the board).  

 

           

This means that the boards will warp, twist, split, swell, and shrink less than in plain sawn wood.  Here are some examples of quarter sawn wood.

 

          Maple                         Poplar                    White Oak                  Red Oak

                                 

These pieces of wood are all quarter sawn and show the annual rings as lines in the wood.  The appearance of the dark part of the annual rings (the Summer wood) is generally referred to as the grain.  The Maple, Poplar, and White Oak photos all show a light sapwood and darker heartwood.  The grain is made of lines that are almost parallel to each other.

 

 

ALTERNATE METHOD OF QUARTER SAWING

 

  The grain (annual rings) in this kind of quarter sawn lumber runs even straighter from one face of the board to the other than in the type of quarter sawing discussed above.  However, there is more wood wasted, so these boards cost more.  [The outer dark ring is the bark.]

 

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Another thinker.

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