Replies

1. 
   StanleyNiemiec | Sep 11, 2002 08:32pm | #1

   Wind (long 'i') can be a problem because it generally indicates more than improper drying, conditioning and equalizing.  I don't recall ever hearing an discussion of spiral grain in cherry so I suspect either a funkie sawing pattern (indicated by excessive grain slope) or lean in the tree (which creates abnormal wood). 

   Abnormal wood is pretty obvious when you see a whole log due to an off-center pith.  To compensate for lean, the conifers grow compression wood below the angle; in the broadleaf, hardwood trees, they grow tension wood on the opposite side.  In both cases the cell structure is different than that which normally occurs.  Instead of an S3 layer, a gelatinous layer is produced.

   Abnormal wood is prone to warp and unless it was properly conditioned, it will retain internal stresses.  These can become manifest in the finished piece or during machining (such that the wood may pinch a sawblade).  The wood tends to be fuzzy as well.

   I recommend you do a prong test.  Go in at least 12" from the end of a board and cut a section about 1" wide across the grain the full width of the board.  Take this section to your band saw and cut out the central core of the board to about 80% of the width so that the two faces are untouched.  You should do this on several boards; boards with wind and flat ones as well.

   If the wood is properly conditioned, the faces remain more of less parallel (that is they do not curve either inward or outward) the board is free of drying and most likely growth stresses.  If the prongs curve inward it indicates unrelieved growth stresses or casehardening during drying.  If the prongs curve outward, it indicates unrelieved growth stresses or reverse case hardening.

   If only the twisted boards react negatively, you have to live with it and find an alternative use for this material.  If all the boards react negatively, take 'em back!  Casehardening is an unacceptable drying DEFECT that will give you fits during resawing.

1. 
   DaleKrech | Sep 12, 2002 01:26am | #2

   Thanks for the explanation! What is case hardening?

   Dale

1. 
   StanleyNiemiec | Sep 12, 2002 04:12am | #4

   As wood begins to dry, it is a non-uniform process.  First the outside dries and then gradually the inside/core of the piece of wood dries. 

   The outside portion contracts against the restraining forces of the still enlarged wet core.   A type of compression stress develops.   As the wood dries further, the core of the piece dries and shrinks.  However the core still has a slightly higher MC than the wood on the surface and therein a slightly larger dimension.

   Exterior "shell" stresses exist and the piece is said to be CASE-HARDENED (the case is harder/drier than the core).

   At the end of a kiln schedule, there are two necessary additional steps  --  conditioning and equalization. 

   With conditioning, additional moisture is added back into the kiln to moisten the outer shell of the wood.   This allows for the shell attain the same level of MC as the core and therein to expand.  If you add too much water in this process, the shell will over expand so that you develop REVERSE CASE-HARDENING.

   Equilization is a step that allows all the pieces to come to a more even moisture content.  During drying some boards dry faster than other.  By stopping the drying process, it allows the wetter boards to reach the desired Equilibrium Moisture Content (EMC).  Basically the drier boards can adsorb some of the moisture from the wetter ones and the moisture content range within the charge (load) reduces.  Sometimes it is necessary to add moisture into the charge to makes sure some pieces are not over-dried.

   Conditioning therefore is a within board moisture content equilibration process; equalization is a between board moisture content equilization.

1. 
   DonaldCBrown | Sep 12, 2002 04:26am | #5

   Stanley-

   Great explanation.

2. 
   thebluesky | Sep 12, 2002 04:55am | #6

   Thanks for taking the time to offer a terrific explanation.  There is so much to learn, you've helped a lot .... John

3. 
   DaleKrech | Sep 12, 2002 06:02pm | #7

   Thank you for taking the time to explain this process.

   Although I'm not a professional woodworker, I've been involved in the craft for over 25 years. Most of what I've learned has come from the FWW magazine, related books and this site (plus a lot of trial and error). I try to do something different in each project to "stretch" my experience. At any rate, after a visit to the College of the Redwoods, I got the "bug" to buy some rough, matched lumber, and give it a try.

   I researched the source from the FWW, and this site, and I think I got some good pieces. But 2 of them (from the same tree) were a little "squirley". I take it that the boards are what they are. In other words, if they are warped, cupped, or have a wind, it's due to the way in which they were dried, and nothing can be done to correct the condition afterwards.

   I think that instead of using these for wide panels, I can perhaps, cut them down into narrower frame pieces to minimize the wind. Can the wind be resawn, or planed out? Or, will the wood keep moving?

   Thanks again!

   Dale

1. 
   StanleyNiemiec | Sep 12, 2002 06:48pm | #8

   If the boards contain unrelieved growth or drying stresses then they were improperly dried.

   During the machining process, as you "open" up that material, you could relieve some stresses and the boards/pieces could distort.  The only way to tell is to either do a prong test or actually machine them.  If during machining, the wood fuzzes, then you will know that it contains abnormal wood.

   Once the piece is dimensioned to final shape, further distortion should not likely occur unless there are large MC changes.  Remember that wood will always move with changes in MC.

   The smaller the pieces, the easier it is to machine them to square.

   If you buy a bushel of apples, produce dealers will put a few bruised pieces of fruit in the mix.  What you want to avoid is an unscrupulous dealer who takes a bushel of bad fruit and puts good looking ones on the top to make it look like you are getting good fruit.  The same applies to lumber sales persons.  The issue is always, are you getting the grade you ordered?  IF you don't think you are, talk to them about it!

2. 
   AlanTurner | Sep 12, 2002 01:44am | #3

   Well, I just learned something.  Thx.