I had some 6/4 red oak resawn so that I could later plane it down to half inch
While waiting to start my project the boards have all warped toward the resawn surface although they were all stacked as they were before sawing
What did I do wrong and what should I do now?
Replies
You didn't do anything wrong. But obviously your 6/4 stock was not uniformly dried. When it was resawn the higher MC on the inside was suddenly exposed to the air, and its drying has caused the cupping that you now see. Wait until it comes to equilibrium and then joint and plane.
Basically you don't have many alternatives. People may tell you to only buy dry stock, or to stack it in the shop until it comes to equilibrium. That can easily take a year or more, and in many cases is just not an option. Having a good moisture meter will at least give you indications of what to reasonably expect when you buy lumber or want to track its drying.
David Ring
http://www.touchwood.co.il/?id=1&lang=e
David I beg to differ. I am SURE you are ALOT smarter at woodworking than I am...
I have been there. Did that. Salvaged some by gluing the cupped faces together to make a new slab.. And of course I started over on the project..
Thanks for the reply.
I have the wood restacked so that the wood is weighted against the bend. I have time to wait but not a year!
Should I plane the "outside" a bit to expose new wood?
Chris,
As has been previously said, there is little you can do. The boards MAY flatten a little, but in all probability they will not. This is a common problem when boards are re-sawn. There are 2 conditions out of a possible 3 that work against the chance that re-sawing will be successful, neither of which can easily be controlled or even discovered until the re-sawing is done.
Note - this is generally not a problem when re-sawing to achieve veneer-thickness results.
The problem is minimized if a board is reduced in thickness by slowly removing equal amounts from each surface - not really an option when going from 6/4 to 1/2" unless you can tolerate all that waste.
Condition 1 -If the wood has been properly dried and the moisture distribution throughout is uniform, re-sawing CAN (not will) result in flat boards. Such drying almost always requires kiln drying and accurate re-introduction of moisture as steam late in the process to prevent case-hardening.
Condition 2 - Case-hardening occurs because the outside of the board loses moisture faster than the inner tissue. If the outer tissue becomes sufficiently dry, it can seal the inside, preventing further escape from that inner "core." That's case-hardening. It VERY often happens with air drying. The board is stable until it's re-sawn. Then the wetter core becomes the outer surface of the 2 thinner boards and they warp, cup and twist.
Condition 3 - Case hardening has not happened, the wood has been correctly dried, but is not yet in equilibrium with the environment in which the re-sawing is done. It has been purchased at a yard and the outdoor ambient humidity is higher than the indoor shop with the band saw.
While case hardening has not happened, there is still a moisture gradient from the outer tissue of the wood to the center. It needs to come to equilibrium with the shop, or re-sawing it will result in serious movement. Although, in this case, it MAY straighten in time as it reaches its equilibrium moisture content.
A moisture meter is NOT as helpful as everyone seems to think. A moisture meter is a very useful tool for the operator of a kiln or even a large air-dying operation. Such work involves moving large stacks of wood around to different "stations" in the drying process. The operator needs to know the relative wetness of each batch one to the other, in order to move them around. THAT's what a moisture meter is good for.
It really is of little use to the individual wood worker who wants to know if the wood he is buying is ready for use. Most meters do not measure more than the surface moisture, no matter what the claims about them by marketing hype. Most workers think there is some magical" target" number such as 7% moisture content, and that such wood is ready for use and stable.
The only moisture content number that's important is that the wood has reached equilibrium moisture content (EMC). That is, it has come to equilibrium with the atmospheric conditions where it is going to be worked.
There is nothing wrong with wood that has a moisture content of 11% if the ambient relative humidity hovers around 60-65%. Because at that RH, the wood IS in equilibrium with the air. Of course, construction techniques must be used that will allow the wood to move as it will if it is exposed to much lower RH. But that's a given.
Using a moisture meter simply tells you that the wood is either exceedingly wet or it has come down into a reasonable range. THEN the only way to know if the wood is actually ready is to weigh it, or a piece of it, and wait to see if it changes weight over a few weeks. If it does not, it is in equilibrium with your ambient conditions. If it does, you MAY have to wait months or years for the weight to stabilize. Until it does, the wood will not be ready for use. It will move when cut. That's just the way it is. Always has been, always will.
But measuring with a meter, or weighing until stable will not tell you if there is case hardening. The only thing you can do is buy from a reputable lumber supplier and trust him while while assuring yourself the wood is otherwise ready and in equilibrium with your shop conditions, by which ever means you are comfortable using. Any reputable dealer should take the wood back and refund your money when case hardening is evident. But many won't unless you're a frequent, high volume customer.
Rich
Edited 11/15/2008 6:13 pm ET by Rich14
Rich, You said, <The only moisture content number that's important is that the wood has reached equilibrium moisture content (EMC). That is, it has come to equilibrium with the atmospheric conditions where it is going to be worked.>I see that you live in central Florida. I would think that the air is comfortable enough to leave the doors and windows open a lot of the time in your shop, which would make it the same as OS air, right? Do you think this is more important than trying to get it to the MC level where it will live after construction? Wouldn't that be the most important EMC?What if the project was going to be shipped to the high plains where it is cold as heck and dry for a long winter season after it was made? It may look good in your shop, only to go to hell in a handbasket soon after it left.
Keith,The wood must reach equilibrium for the WORKING conditions. Not for the environment where it might eventually get used. If it is not in equilibrium for the shop conditions, it will move during construction. That's intolerable. There is no way to achieve any kind of accuracy under such conditions. Wood prepared true and square today will be out of that condition by tomorrow.On the other hand, the construction techniques must ANTICIPATE wood movement in the finished work for any environment into which the piece may be put. Such techniques are always be part of the planning and execution. That's part of learning how to build.My shop is air conditioned. I could NEVER work under the climate conditions that prevail here. Except for a few weeks of the year. But furniture I make, or that any competent furniture maker makes can easily withstand going from the extremes of Arizona summers (RH 10%) to a heated house in Arizona in the winter (RH below 3%) to Florida summers (RH 90%+). I have a houseful of furniture that proves that. Things I've made and things I've bought. It's all doing fine with nary a crack or split.Actually, the only thing that has warped is the base of my work bench! And that's because I laminated the legs to achieve the thickness I needed and built them of 2 laminations instead of properly using 3.Rich
Rich, I have only spent one winter in Fl, and I made an assumption which may not have been right, based on my experience. Like you made the assumption that everyones shop has a controlled atmosphere comparable to the final destination of the piece, at least as I read it. Neither of us would have been right.I feel sure that there are plenty of readers of this forum who are working in less than perfect controlled atmospheres in their shops, who need to understand the difference between what you stated, if they are working under other circumstances.
Keith,You completely misunderstood my reference to my air-conditioned shop. I was simply saying there was no way I could work in this climate without air conditioning, most of the year. The summers are brutally hot and humid. They have to be experienced to be believed.In the winter, I need heat in the shop as it frequently gets down to the mid teens overnight.All that has nothing at all to do with the subject of wood moisture content and need for the wood to reach equilibration moisture content.Whatever the atmospheric conditions in which the wood is being worked, the wood must be in equilibrium with the humidity of THAT atmosphere (the ACTUAL work shop environment) for accurate work to be done. If the shop's windows are open, it's RH is about the same as the outdoors. If it is closed and climate controlled, the RH is whatever the climate control equipment makes it. The wood must come into equilibrium with either of THOSE conditions.AND . . .the design must be such that the finished piece can expand and contract without self-destructing when and if it is placed in an environment that has significantly different atmospheric humidity than that in which it was made. It also has to survive possible subsequent changes, but that's just re-stating the same thing.Rich
Edited 11/15/2008 11:44 pm ET by Rich14
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