Replies

1. 
   kennedy136 | Jan 16, 2003 12:24am | #1

   Mwinkle,

           Welcome to the world of woodworking.  What you did by ripping a wide board into several narrower ones was to release stresses contained in the wide board.  Could have been a piece of "reaction wood" which comes from leaning trees, placing one side of the tree in tension and the other in compression. Could also have been stresses induced by the drying process.  Some boards tend to move more than others.  One thing to consider when ripping narrow strips, it usually,not always but most of the time, is better to rip them out of narrower pieces like 1 x 4's or 1 x6 's than to rip them out of wider stock.  Wider stock has a greater tendency to move when cut into narrower strips.  Lesson learned.

                                                       Mark

1. 
   mwinkle | Jan 16, 2003 06:13am | #3

   Thanks for the intelligent ,informed response.  A rather expensive lession at 8.75/bdft.

   I'll talk with the supplier tomorrow.

1. 
   kennedy136 | Jan 16, 2003 07:47am | #6

   Mwinkle,

         You may find that you can save money by buying narrower widths when you are planning to rip them down anyway.  Wider boards usually command a premium and are best left wide for drawer fronts, panels, case sides, etc.  Try to plan your cutlist accordingly.  BTW 8.75 per board ft for cherry?  I think they saw you coming. I rarely pay more than 4.50 and that is for extra wide.  Then again I buy a lot of wood from that supplier.  Built a highboy this fall and got 1 board that finished out at 17 inches wide with no sapwood.  Whenever he gets a fresh load of cherry or walnut I go and raid the pile.  Nonetheless 8.75 is steep indeed.

                                     Mark

   Edited 1/15/2003 11:51:12 PM ET by the professor

2. 
   StanleyNiemiec | Jan 16, 2003 03:08am | #2

   Reaction wood could be a problem but the most likely culprit is poor drying practices  -- specifically failure to adequately condition the lumber at the end of the kiln drying cycle. 

   I consider residual stress in lumber to be a defect and I would comment to the people who sold me the material.  The reality is that if you don't tell them that this defected material is unacceptable, they will continue to sell it to unsuspecting individuals like you. 

   The people running the kiln are cutting corners or are ignorant of proper drying practices  --  they will continue to do so until their suppliers start complaining that their customers are complaining.

   Reaction wood tends to get fuzzy during machining so you might want to check your edges/surfaces.

1. 
   forestgirl | Jan 16, 2003 06:14am | #4

   I've had this happen with thinner, smaller pieces of KD lumber.  Question:  Assuming the original piece is straight and true, if it's allowed to sit in a good environment (humidity-wise) for a number of weeks (or months?) after it's brought home, will those drying-induced stresses be alleviated, or are they there to stay?

   My last bad experience was taking 3-1/8" x 5/8" backsplash (oak) and ripping it down to 2".  One of the pieces just curved away from the other as it left the tablsaw.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   jonsherryl | Jan 16, 2003 06:32am | #5

   Forestgirl, you've addressed Stanley on this, but I'll chime in. Drying stresses induced by improper kiln procedures don't go away.

1. 
   forestgirl | Jan 16, 2003 08:58am | #7

   Thanks Jon, I'm glad you saw my question.  I think I'm gonna have to go somewhere else for my oak, because that particular place seems to have a lot of problems with their stock.  I comb through a couple or 3 dozens pieces of wood like that backsplash and find maybe 3 or 4 pieces that are straight and don't have that greyish tint in them, and even then I get wild wood!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   StanleyNiemiec | Jan 16, 2003 10:03am | #9

   The greyish tinge is something called grey stain (a defect).  Grey stain is caused by a bacterial infestation and it occurs because the wood surface remains too wet.  The wetness allow the organism to colonize/infect the wood and it is metabolizing some of the simple soluable sugars.  Most often it appears in patches and makes the board look blotchy.  It is definitely a surface phenonemon so that if you cross-cut through an area of stain it will not generally penetrate much more than 1/16th of an inch (except around knots and surface checks).

   If wood is dead stacked green off the saw or is "air-dried" in unfavorable (cool, high-humidity, not enough air flow) conditions especially in the early stages of drying, grey stain will develop.  It does not affect strength properties but it is an unacceptable DEFECT. 

   It is sometimes very difficult to see in rough sawn stock and unfortunately, the penetration is generally deeper than normal/acceptable planing/surfacing allowances.

   It does not surprise me that wood with grey stain also has unrelieved/non-conditioned drying stresses.  To me it is obvious that the people manufacturing the lumber, don't know what they are doing.  No matter what the grades they are producing, it is inferior product. 

    

2. 
   StanleyNiemiec | Jan 16, 2003 09:47am | #8

   Drying stresses are usually case hardening or reverse case hardening.  They USUALLY will not go away with time unless the wood is going through some pretty severe EMC cycling.  If this happens after a piece of wood is in some furniture, it can contribute to excessive deformation (WARP).

   The explanation is not simple and easy so please tolerate my seemingly excessive verbiage.

   When wood dries, it dries from the outside in  --  that is the surface loses its moisture before the core loses its moisture.  We all know that wood shrinks as it dries so as the outsides surface dry, this part of the board shrinks  --  except it cannot do so totally because it is restrained by the core.  To compensate, the wood, sometimes, will fail in shear and you will get surface cracking; or sometime, the wood will fail in compression (in the core) and you get collapse. 

   As the wood continues to dry, the moisture content of the core decreases, and therein shrinks.  The exterior surfaces have taken a "set" (the case of the board has hardened and is stiffer/stronger) retaining its shape and retaining a certain level of compressive force. 

   The core will likewise take a "set" but it is entirely different from the surface.   The core will shrink but to a degree, it is restrained by the wood on the surface.  This creates tensile forces unless they have been "relieved" by minute wood fractures (which is how internal checking occurs [partially and simplistically]). 

   All these residual forces in the wood can create some truly bizarre shapes to the unsuspecting woodworker stuck with a load of non-conditioned wood.  It will bend out of the saw; it will pinch in the saw.  If you plane/surface one side more than the other you can end up with boards with so much bow you could use it for chair rockers.

   Conditioning of lumber occurs (should occur) at the end of the kiln cycle.  Moisture, often in the form of steam, is added to the kiln for the purposes of increasing the moisture content on the surface of the boards.  This allows the surface to soften a bit and to slightly swell and therein relieve case-hardening (as well of closing some of the smaller, slight surface check).  Too little is not enough, it has to be just right because if too much moisture is added, you get a condition called reverse case hardening where the stresses have not been equalized but instead are reversed.

   If you take a board about 8 to 10" wide and cut (across the width of the board) about a 1" wide strip at least 18" from an end, you can do what is called a "prong test".  Take this strip to your band saw and lay it on the end grain surface.  Cut out the core of this strip leaving about 1" of undisturbed wood at one end.  For a 4/4 board you want to leave about 0.2" of surface material undisturbed and you sort of do a crossing cut at the end (base of the retained part).  This is not fine woodworking, you just want to cut out the core.

   After you cut out and remove the core, the prongs should, more or less, remain straight (though a slight bit of inward curvature is acceptable).  However if the prong tips curve inward so that they touch each other -- you have got a casehardened board.  If the prongs spread outward, then the board has reverse case hardening.

   I hope this makes sense and explains drying stresses, case hardening and reverse case hardening.

   Edited 1/16/2003 2:07:22 AM ET by NIEMIEC1

3. 
   jgaiennie | Jan 16, 2003 03:08pm | #10

   This movement can be anticipated in much of the lumber you will cut.  I find I often get wood "movement" when I saw a vertical grain rip off of the edge a board that is mostly flat sawn.  When I do this, the two pieces generally tend to bend toward each other as they are ripped.  The solution is to anticipate this movement by ripping the piece wider than you'll need, releasing most of the stress and allowing it to bend as it may, then straight edging that rip and ripping it again, repeating the process until you have a straight rip the width you need.  Of course the hard part of this is two fold 1) knowing how much extra width to allow for to accomodate the bending and straightening, and 2) paying for all that sawdust and shavings at $8.25 per bf.  You'll have to work that out on your own.

   jdg

1. 
   mwinkle | Jan 16, 2003 05:42pm | #11

   thanks for taking the time to provide a considered response.