Joining wood or use plywood

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  #1  
Old 08-11-03, 09:46 PM
TKEcowboy
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Joining wood or use plywood

I am about to build an entertainment center out of Pine. A friend at work heavily suggested using Pine plywood instead of trying to join pieces for the back and sides. he said Pine is one of the worst woods for shrinkage and said that over about 5 years a board of Pine may shrink about 1/4 inch. Is this true? I really like the look of joined wood because it gives the project that authentic woodworking look. Should I use Pine plywood instead? A local wood specialty shop carries 4x8 sheets of knotty Pine plywood. Would it be best to use that? Thanks.

Glenn
 
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  #2  
Old 08-12-03, 06:54 AM
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Welcome back.

All wood will expand and contract across the grain as the moisture content changes. It changes by a percentage so that wider boards move more than narrow boards. This is one reason why furniture it made of narrow strips glued together rather than one wide board. The layout of the wood helps balance the pressures exerted when the individual boards change. Many times the boards are alternated with grain up and grain down to help balance the tendency of plainsawn wood to cup.

Frame and panel doors and other components that are made with solid wood panels have an allowance for the panel to move within the frame. The panels are not usually glued into place. If the panels fit snugly from side to side, the frame may be forced apart when the panel gains moisture and expands.

The materials for hardwood floors are usually left on the site for a while to stabilize to the relative humidity. This also explains why hardwood floors have a margin of space left between the edge of the floor and the wall. If each strip of flooring expanded 1/32" when the moisture content rose enough, the 96 boards in a 20 foot wide room could expand 3 inches all together. This would require a fair change in moisture content, but the possibility exists. This is an extreme example.

The change along the length is almost inconsequential.

Plywood is more stable than solid wood because the plies of veneer run at right angles to each other. The glue helps prevent the expansion and contraction. The lesser mass of the thin plies reduces the pressure when the moisture changes. All in all, this makes plywood more stable dimensionally than solid wood.

Wood that is kiln-dried has a low moisture content around 8 - 11%. When it sits in the vendor's rack, then in your shop waiting to be used, it balances with the humidity there.

If you use kiln-dried wood, you should be OK. The movement in the wood will balance out, if you think about it. When you study about building furniture and gain experience from the work, you will come to better understand why things are made the way they are.

Some examples of allowing for wood expansion are: loose panels in frame and panel construction, breadboard end pieces glued only in the middle.

Go ahead and make the piece the way you prefer.

Feel free to bring your questions back.

Hope this helps.
 
  #3  
Old 08-12-03, 11:30 AM
TKEcowboy
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I'm beginning to think that it would be best for me to use plywood sheets and wait until I have more experience joining wood before using smaller pieces. My biggest concern is whether or not the overall appearance of the outside of the entertainment center will look as good when made from Pine plywood as opposed to joined pieces. Can you really see the grain in plywood like you can smaller pieces. Also, will Pine plywood really LOOK like Pine wood? Thanks.

Glenn
 

Last edited by TKEcowboy; 08-12-03 at 01:35 PM.
  #4  
Old 08-14-03, 06:48 PM
brickeyee
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Pine is typically rotary cut to get veneers for plywood. You might be able to find some furniture grade plywood faces that are flitch cut. In rotary cutting the log is placed on a machine similar to a huge lathe and a blade is pressed against it. As the log is rotated the wood peels off in a huge spiral cut. It produces 100% flat cut wood grain. Flitch cutting involves moving the wood past a stationary knife and removing a slice at a time. Wood can range from flat cut to quarter sawn depending on what the veneer manufacturer wants. Furniture grade plywood also has either better core layers, or the best has a lumber core made of strips of wood glued up instead of veneers. Pine tends to blotch when stained, and the water needed to soften the wood for rotary cutting makes this problem worse. You should finish up a sample before starting your project to make sure you will like the final finish.
 
  #5  
Old 09-30-03, 06:39 PM
Projectmgr
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If it's long term your concerned about.

Go with the plywood .
 
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