Replies

1. 
   jazzdogg | Feb 13, 2004 06:04am | #1

   Whiz,

   I've successfully dried chair spindles, riven from green wood, in a cardboard box in which a 100-watt lightbulb was inserted. In about a week, the moisture content dropped from around 30% to less than 10%.

   You might want to try stickering your wood and covering the whole shebang with a cardboard box w/ bulb. If you check it fairly frequently (daily), you shouldn't have too much to worry about.

   Good luck,
   Jazzdogg

    

   Whether you think you can, or you think you can't, you're right.
1. 
   whiz | Feb 13, 2004 04:31pm | #2

   Thanks for the information. I've read all of the postings from this site as it relates to drying wood and I realized that it is truly a science. I know more about the molecular structure of wood, what lignin is and the procedures of kiln drying than I will ever need to know...especially from "Niemiec1".

   A few questions:

   Have you ever measured the temperature inside your "drying area"?

   I don't have a moisture measuring device. Do you think I need one?

   Do you worry about casehardening? I was all set to sticker the pieces near my furnace (I'm convinced that New England is now in a yearly permanent freeze) but I have now been scared off from doing this.

   My biggest problem is that I am trying to leave the bark on so I am pretty limited as to how much I can do after the piece dries to finish the piece.

   Thanks again for the suggestion. I guess I will just have to try a few techniques and see how it goes.

1. 
   OneofmanyBobs | Feb 13, 2004 05:26pm | #3

   A lot of what is called case hardening is really burnishing from the planer.  I don't worry about it.  Cooking the wood too hot isn't good.  Commercial kilns often have the opposite problem since energy costs money.  I use an old dehumidifier.  It generates enough heat to warm things a bit and gets rid of the water.  You probably should have a moisture meter.  Otherwise you have to weigh the pieces to tell when they're done.  Although, that's a good method.

1. 
   jackplane | Feb 13, 2004 06:13pm | #4

    Case hardening is NOT caused by burnishing from a planer.Rather, it is the result of internal stresses within the wood, often caused by irregular growth, or growth under stress, such as on the side of a mountain. When case hardening is encountered, the best defense is to use a splitter on the tablesaw.

1. 
   OneofmanyBobs | Feb 13, 2004 07:50pm | #5

   Internal stress is just the nature of wood.  I don't consider that to be case hardening.  Cut a slice from the middle of a thick plank.  Cut that slice again and it will move, warp, twist.  Depends on the piece.

    I interpret case hardening to effect only the outermost skin of the wood.  Rarely I see lumber that has been processed so that outer eighth or 16th is harder than I expect.  Maybe because the natural resins have been cooked.  Mostly I see people complain that stain doesn't take evenly because the surface is burnished and they incorrectly call that case hardening.  When lumber is dried rough and planed, you mill away the part that could truely be called case hardened.

2. 
   jackplane | Feb 13, 2004 09:06pm | #7

   First, case hardening is not warp nor any of the four kinds of warp. What you "consider" to be case hardening is far from the definition of woodworkers, architects, or the Forest Products Council.

     Case hardening has nothing to do with the outermost layer of wood. It is not part of the wood at all; it is a condition that can affect one's ability to safely cut the wood.

     If the outermost layer of the wood dries before the inside,as can happen when steam is not injected into the kiln, then case hardened wood often results.

   Edited 2/13/2004 1:34:33 PM ET by JACKPLANE

3. 
   OneofmanyBobs | Feb 13, 2004 10:51pm | #8

   Well, whoop-de-do for what the "woodworkers, architects, or the Forest Products Council" considers.  Case hardening is when the outside is hard and the inside is soft.  Just like in metalwork.  I can cut wet lumber or kiln dry lumber and have it rack.  Thats just how wood behaves.

4. 
   jjf | Feb 13, 2004 11:37pm | #9

   The true definitions of words are important because they enables us to communicate accurately and avoid confusion.  If our intended thoughts are  not transmitted why talk?  With that said.

   Casehardening is not cause by heat or burnishing by tools. It is not caused by irregular growth.  It does develop in all wood dried.  The surface is not harder than the center.  The term came from the people researching wood drying at the turn of the cetury, no not this century, the last one  ~1900.  They were trained as mechanical engineers and had experience with metal design and manufacturing.  They barrowed a term that was not completely accurate.  Casehardened metal is harder on the outside but also the surface is under a compression force.  It is the compression force on the outside that is similar between the wood and metal, only.

   Casehardening does not cause stain being taken up unevenly.  While burnished or heated wood will cause this.  Along with other causes.

   As all wood dries, the outside dries first and faster than the center.  The center resists the shrinkage the outside first goes through.  This resistance "streches" the outside, making it bigger.  As drying continues, the center starts to dry and it too tries to shrink but is resisted by the "streched " surface.  So the result is the surface is in compression and the center is in tension - "casehardening.  Yes this is the way all wood behaves. Not only irregular growth wood.  The portion of wood that is under compression is about the outter 1/16 or 1/8 ".  With the removal of this material from both sides casehardening is removed.  Typically, the process of stress relief (sometimes called conditioning) is done in the kiln after what is called equalization.  Stress releif is performed by injecting steam into the kiln quickly.  This causes the surface to try to expand but is resisted by the center and the surface is "sqwished" to its' original size - removing all the drying stresses.

   If the wood is not intended to be resurfaced such as construction material there is no need to remove the casehardening.  This is true if the spindles are preshaped and no additional material will be removed.

   If a layer of wood is taken out of the center and then split in half it should not change shape immediately.  If the moisture content changes it is likely to change shape but this is not called casehardening.  It is just the normal behavoir of wood, shrinkage and swelling.

   It really does not matter if you get a scale or moisture meter if all you plan on doing is drying small pieces.  But you need something to tell you what the moisture content is .

2. 
   jazzdogg | Feb 13, 2004 08:52pm | #6

   "A few questions:

   Have you ever measured the temperature inside your "drying area"?

   I don't have a moisture measuring device. Do you think I need one?

   Do you worry about casehardening? I was all set to sticker the pieces near my furnace (I'm convinced that New England is now in a yearly permanent freeze) but I have now been scared off from doing this."

   Whiz,

   In response to your questions:

   1.  I've never measured the temperature inside the cardboard box;2.  A moisture meter that's accurate, especially in the low range, it an investment I would endorse;3.   My chair spindles are completely shaped when I place them in the box, so case hardening hasn't been an issue (A dry spindle has shrunk enough to make insertion into the mortise fairly easy, and, after insertion, the dry spindle absorbs moisture from the still-green legs, locking the joint together very tightly);4.   As to placement near your furnace, I believe that could be problematic because without the wood in an enclosure, and with the furnace cycling on and off, different parts of your wood will be at markedly different temperatures/humidities simultaneously. The bulb in the cardboard box is on all the time, keeping the temperature and humidity within relatively consistent.5.   I'd worry about end-checking if the wood hasn't already been air dried. Even if it has, I'd probably coat the ends of each board with wax as a preventative measure - it's cheap insurance.

   Good luck,Paul

   Whether you think you can, or you think you can't, you're right.

1. 
   whiz | Feb 13, 2004 11:40pm | #10

   Wow, I feel like I'm back in Engineering School. I thought, then, that you just designed a product and that was it. I didn't think that I had to worry about strength of materials, heat transfers etc.etc. etc.

   One of my boys just finished a course (one of several he has taken) at the North Bennet School in Boston. I wish he would spend his money on a graduate degree. ;o)

   I don't know what the course was but he watched me planing a board and then looked irreverently at me and said it was going to warp because I only cut from one side of the board, exposing an unequal amount of moisture from one side to the other. I should have taken a 64th off of each side rather than a 32nd off one. So much to learn!

   Anyway, I like your idea about the cardboard box and lightbulb. I guess I will have to go out and buy a WC meter and a new drill press ( so I will have a box large enough!). Think my wife will go along with that excuse?

   Thanks for all of the help. I'm an intermediate woodworker who is beginning to think I haven't made it out of the ranks of beginner. Finishing is our specialty but I thought manufacturing products would fill in the time gaps in-between buying, refinishing and selling. Product to refinish is getting harder and harder to find with other "Wrinklies" like us retiring and getting into the business.

1. 
   jjf | Feb 13, 2004 11:50pm | #12

   Your kid is partly right.  By planning only one side you remove the compression only on that side and the wood will respond immediately from that removal.  The wood will not gain moisture faster on the planned side as compared to the other side.  If the board did not warp immediately, it was not from the drying stresses. 

    If the board gains or losses moisture it can warp.  If it changes evenly from both sides and the board is flat sawn it will cup.  If it changes moisture from only oneside, say because it is laying on the table, it will cup then also.  These moisture related cuppings will occur over time, say overnight.

   Edited 2/14/2004 11:13:11 AM ET by jim

2. 
   jjf | Feb 13, 2004 11:43pm | #11

   All you need is a contained space that you can control the temperature and humidity to some extent.  Be it a room, box or small chamber made out of 2x2's and sheet of plastic.  The heat source can be an electric heater (careful of fires) or hot water pipes running through it.  At this time of year inside most persons' homes in the northern hemisphere it is very dry and you may need to slow the drying a bit by keeping the enclosure closed and opening it now and then or wrapping the wood in newspaper.  This is if it is a surface check prone species like oak or sycamore.  Other species, like maple, need to be dried fast to avoid staining.