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Wood Humidity

Discussion in 'Luthier's Corner' started by eleonn, Dec 26, 2006.


  1. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    A few days ago I bought the purpleheart blank for my first project. I had to put Lima upside down to find this wood because almost the 100% of it is exported so when this guy had no problem in selling it to me I didn't thought about it twice. It is 110"x4"x1" (and it cost me around $2.7 which was much more cheaper than I thought it would be :hyper:). When I asked about the % of humidity he said 15% more or less. I bought it becuase it will be harder to find something better. I have read in several places that woods should be at 10% or 12%.

    Should it be a problem to work with woods with 15% of humidity? It's summer here but here we usually breath water the whole year and I don't think that somebody will accept to put my blank on their kilns. Some friend told me to put it under the sun at the day and put it in a closed place at night when the humidity rises.

    What do you guys think??
     
  2. Nelson Guitars

    Nelson Guitars

    Aug 14, 2006
    Novato California
    Custom builder
    You may want to get a moisture meter and test this material before using. These can be pricy instruments so see if you can borrow one first. Many high school and college shops will have one but you will probably have to take the material there instead of bringing the tool to your shop.

    Wood shrinks a great deal when it dries. If it hasn't finished drying, all your good work can be for naught as it continues to dry and shrink after you are done. Kiln dried material should be between 8 and 10 percent moisture. Air dried material can be as high as 12 percent. If that is the case you may only need to put this up for another year or two until it is ready to use.

    Don't put this wood in the sun! The surface will dry and shrink faster than the core and will check (split). If it needs a year or two of seasoning then be patient and find something that is ready now to use now. You will be glad you did.

    Greg
     
  3. Greenman

    Greenman

    Dec 17, 2005
    Ontario Canada
    Is there a way to speed up the process for individuals that don't have access to a kiln?
     
  4. Nelson Guitars

    Nelson Guitars

    Aug 14, 2006
    Novato California
    Custom builder
    Short answer is: No, there is no quick dry method that an amature can use to dry wood fast.

    Kiln drying is both art and science. It is not reccomended for those who are not properly trained. Even at that, if you go too fast, too slow, increase or decrease the temperature too fast or get any of several other factors wrong the result can be a big pile of kindling. Drying is also species specific. You do different things to dry fir for framing than you do to dry something like Purple Heart.

    This can be really frustrating for someone starting out who just wants results. I find it rewarding however to pull something down from my rafters that I haven't seen for five or so years and have it be just what I was looking for. It may just be in my head, but I find air dried material works in a superior fashion to kiln dried. Especially when I build acoustics.

    Greg
     
  5. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    I don't think I be able to find somebody with a moisture meter and I really doubt that any high school should have one at least here in Peru. I guess I will have to buy another blank or see if I can find someone who accept put this one on his kiln :(.
     
  6. vintager

    vintager

    Jan 29, 2005
    Slovakia
    +1

    just don't work with 15%.

    good luck


    mike
     
  7. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    This has a suggested kiln drying schedule, if you are able to use a kiln and get the owner to follow your wishes.
     
  8. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    I went to my place to have lunch there a take this blank out of the sun and after two days guess what??? it already have some cracks at the edges. Nothing to be worried about. I can cut 2cm form each edge and everything will be ok.

    Now for less than $3 I guess it will be easier just to buy another blank. I'll ask this guy if he have any blank at 10% - 12%. If he doesn't, there is this place about 45 minutes from my place who have every kind of wood I need. I sent an email once asking if they could sell me small amounts of wood (only enough for my first project) and they said they couldn't. But this guy I bought this blank from told me the same thing by mail. The problem with this place is it seems to be pretty big, the have 10 kilns here, 2 in US and one in Mexico and almost all the lumber they have is exported mainly to US, so I'm not sure if they will want to sell me about a few blanks of wood :(
     
  9. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    I forget to comment this: The guy from this place told me that this blank won't get more dried than it is this right now but only with a kiln.

    Lima is around of 90% to 100% of humidity the whole year. So what will happend with a 10% moisture blank?? It's moisture will increase in time?
     
  10. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    OK, this is my understanding of it:

    When wood is left in the open air, it acclimatizes. This is something that you generally want to happen. It means that whatever its moisture content was, it eventually reaches an equilibrium level, determined by the humidity of the surrounding environment.

    So, raw wood will loose moisture, and any very low moisture wood will gain some. This continues until it reaches equilibrium level, a level that can be lower if you live in an arid area, or higher if you live in a damp area.

    Generally, you want all wood to acclimatize and reach that level before you do any work with it. That's why people buy air- or kiln-dried wood, and then store it for at least a few months before using it. The thicker it is, the longer it must be left, so that it will be uniform through to the core.

    The only reason I can imagine you might not want it to acclimatize would be if you know that the final destination for the instrument is very different than your own. I would guess that there's a risk involved in doing this.

    I know of a veneer-inlay cutter who will, on request, acclimatize to a different temp/humidity before cutting. Luckily, veneer acclimatizes relatively quickly because it is so thin.

    I think I remember one builder in the southern USA, living in a hot, humid area, who keeps all his wood in a climate controlled room, and takes it out only to work on it, and then returns the instrument-in-progress to the room.


    Does that sound right, builders?
     
  11. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    Ok. its supposed that I have to buy the blanks for my project and start with it in a few months so the wood can reach a some moisture level????

    This blank of purpleheart and the blanks of congona (south american wood close to maple) and walnut that are supposed to be here in two days were for sure kept in open air for some time until I bought them. There's no way to know how much time were like that so god knows if they reach a moisture level or not.

    I have read over internet about a guy living in new jersey who keeps all his wood inside a closet and left a 50watts light turned on. He only take his wood to wok with it and then put it back in the closet.
     
  12. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    When I make chairs from green hardwoods, I place the rungs and spindles in a cardboard box kiln to dry after I've shaped them slightly oversize with drawknives and spokeshaves; this "kiln" is just a cardboard box, about 3' per side, lined with aluminum foil (shiny side facing in), into which a lightbulb has been inserted. The chair parts are suspended on a wire shelf at mid-kiln to promote uniform air circulation.

    When drying wood, proper support can be critical in order to avoiding warping. After I've sawn green logs into rough lumber using a Woodmizer bandsaw mill, the boards are carefully stacked and stickered to promote uniform air circulation; then, concrete weights are place on top of each load to hold the topmost boards flat while drying.

    The distinct differences in the sounds they make when tapped together is a huge clue as to whether your sticks are wet or dry.

    With or without a kiln, if you weigh a test piece every day and log its weight, you'll know when other pieces of the same thickness have reached EMC (Equilibrium Moisture Content) because the weight will stabilize. If you size your test pieces appropriately, you can infer the MC using weight tables found on websites and in books like R. Bruce Hoadley's "Understanding Wood" (ISBN #1-56158-358-8).

    You can also measure the thickness with a pair of calipers to detect when shrinking slows to a crawl. There will be twice as much shringking across the grain of a plain-sawn board as there will be across the grain of a quarter-sawn board, so pay attention to the grain orientation when you position your calipers, and always position your calipers in the same place in order to acheive consistent and meaningful measurements.

    The good news is that is doesn't take long to go from 15%MC to 12%MC. Most lumberyards and furniture makers use a moisture meter everyday, and will have already established reasonable base-line MC for their most frequently used wood species. They'll be able to tell you what's "normal" in your area, for a given species, at a given time of year.

    Good luck,
     
  13. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    So I may check if the blanks shrinks with a caliper and if there is no shrink at all in any of the blanks it's because they reach already some equilibrium? I won't do that with this purpleheart blank but I will with the ones to come tomorrow.

    How much time takes to go from 15% to 12%. A friend who worked in the Amazonas rain forest told me that blanks with 1" should be Ok in a month or two max.

    I think that the importat thing here is that I should not work with wood that I just bought and let it to acclimatize at my place as Pilotjones said. I didn't have that time period in mind when thought about a schedule for my project ...I thought that a few days would be just Ok :(
     
  14. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    As has been said, you need to always measure the same place(s) on the board. A chalk or pencil mark will help with that. You'll need a precision (to .001") caliper. Keep measuring until there is no change over a period of time.

    If the wood was very dry, and your climate is damp, you may even see it grow rather than shrink.

    Since your wood is 1" thick, it may take a while to stabilize.
     
  15. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Maryland
    Owner: FBB Bass Works
    I believe others have said parts or all of this. Anwyay,

    Wood contains two types of water. Free water (in the cell cavities) and bound water (in the cell walls). Each wood has a different "fibre saturation point" that is the point at which all the free water is gone from the wood. Purpleheart's fibre saturation point is roughly 17%.

    Here's the important part(s): once the free water has been driven off, it doesn't come back unless you soak the wood in water. It is the bound water content of wood that fluctuates with humidity and temperature. When ambient conditions change, the wood will take on or give off bound water to reach the "equilibrium moisture content" (EMC) for that combination of wood, temperature, and relative humidity. So, you could expect the MC of purpleheart to go as high as 17% in super hot and damp conditions.

    What does it all mean to you? (1) your wood may already be at EMC, in which case (2) kiln drying is probably a waste of time, since it will return to EMC after coming out of the kiln at 10%. Many woodworkers (esp. guitarmakers) use a combination of humidifiers and dehumidifers to keep the relative humidity in their shop/wood storage areas in the range they expect the finished piece to wind up in. So, (3) if your bass is going to stay in Peru, then you want the purplheart's MC to reflect what is normal there. Otherwise you will need to control the ambient conditions where you store the wood to control the EMC.
     
  16. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    I guess those are good news. I will buy some extra wood anyway in case I screw up something and if not when I decide to build a second bass they will be at an equilibrium moisture level. I'll try to find some blanks at 12% moisture level.

    The bass will stay in Peru close to me and nobody will touch her!!! :mad: :p

    Well I supossed that means that I can work with the blanks I bought so finally I can send all them to be cut to the dimensions I need and start to glue them up!!! :hyper::hyper:

    ...this is exciting!!!:)
     
  17. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    If you are very lucky, and have good karma, you will be able to find someone who operates a vacuum kiln in your area. As I understand it, vacuum kilns were initially WoodMizer's initial bread & butter.
     
  18. eleonn

    eleonn

    Aug 24, 2006
    Lima - Perú
    Yesterday I went to visit a friend. His parents owns a lumberyard in peruvian rain forest. I cut about 20cm from my blank, took with me and showed it to a guy who work in the branch office here in Lima. This guy who used to work in the lumberyard saw it and told me the blank is already dry and it won't get more dry because Lima's weather but using a kiln (if I find someody who accept to do this) and after taking it out the blank would gain more humidity from air until reach the level is in now (exactly what FBB said).

    The told me that you can´t put different wood species in one kiln because they get dry in different ways and all the wood have to get into the kiln at the same time. A plus against me is that purpleheart is a really really rare wood here in Lima so it will be difficult to find someone at the right time to put my blank on a kiln to get it more dry and after that the blanks moisture will rise anyway.
     

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