The Forestry Forum
General Forestry => Drying and Processing => Topic started by: Dave Shepard on September 03, 2007, 10:00:16 PM
-
I am going to be sawing some oak and cherry soon, and I will be stickering it in my machine shed, 40'x96'x12'high. Only the front of the shed is open. I know too much air flow is bad, but am I going to have to worry that I am not getting enough? I will be sawing 4/4, 5/4, and maybe 6/4. Will I be able to use air dried hardwoods for furniture building once I have brought it into a heated shop and normalized it to a low MC? I know that some species, like pine, should really have the pitch set at a fairly high temp, like 160 F. Thanks for any input.
Dave
-
A wrap of ShadeDry, or construction entrance fabric, or silt barrier is
the best solution to too much low humidity air flow. Remember that
it is a combination of wood species, air flow, and relative humidity of
that air that is the critical combo.
Phil L. You can quickly wrap or unwrap, if you so choose.
-
you should be fine if the 'back' of the shed it to the prevailing wind, but if the breeze blows right into the front, you might need to wrap it.
If you don't have enough air circulation, mold and fungi will grow on it. By the time you see it growing, it has already caused stain.
If you have too much air flow, it will check. Again, by the time you see it, it is too late.
It will take one year per inch to bring it down to 12-13% moisture. I don't know how long it will take in a heated shop to bring it down to 6-8%, maybe someone with more experience with that end of it can help with that answer.
-
I have seen the phrase "setting the pitch" a few times in the forum. Does heat cause it to cure somehow?
thanks for the education!
sawdust
-
I guess you would call it "curing", after a fashion. What the heat does is boil off the volatile chemicals that will evaporate at that temperature. Once they are gone, the wood won't "bleed" at that temperature or below. The higher temperature you are able to obtain and hold will directly affect the temperature at which the sap is "set".
Setting the sap doesn't mean much unless you know at what temperature it was set. If you get a piece of pine with the sap set at 80 degrees and install it in a window box where the sun will hit it and it reaches 130 degrees, it will probably bleed. The volatiles had never been boiled off to the temperatures reached in the installation.
-
What Tom said. That was a good explanation of the process as I understand it. I can only add that the wood needs to be at the pitch setting temp for a period of time. The volatile parts of the sap don't just magically disappear when you reach that temp, they just begin to dissipate there. I haven't found anyone who could tell me specifically how long, but 16-24 hours seems to be a popular theory. I think that would be starting when the internal temp of the wood reaches that level, and not just the air temp in the kiln.
Somebody correct me if I'm wrong on this. Don P? Beenthere? Den Socling? You guys have done some homework on this. What say ye?
Getting back to the original question...Dave, how soon will you be putting your wood in the shed? I would think you'll be seeing some lower temps before long, so air circulation won't be quite as important to prevent mold. I'm thinkin' I heard you don't have to worry too much below 50 degrees. It might not hurt to have a small fan in there just to keep the air from getting too stagnant, though.
-
I air dry in my shed quite a bit Dave, I try to time it to the seasons though. The cherry I wouldn't worry too much about but the oak I would. You don't say if it's white or red but I have the most problems drying white. This time of year I'd probably wait another month to to it.
On the cherry I'd stack it in an area that does not get hot wind in the door and after a couple of weeks get some fans on it until the weather cools down some. You kind of have to use gut instincts with how much heat is too much versus worrying about mold.
On the oak I'd wait to cut it until it cools down, probably mid October. I personally don't cut wo until November that's to be air dried. Now most folks will tell you to put it into a kiln as soon as possible and for degrade it's true. I do get quite a bit of sales because I only air dry it and specifically tell folks that. Lots of arts and crafts folks like it that way. I use air dried in my projects all the time and have very few problems with the wood. I do make sure to equalize it in the shop for some time.
-
DanG
Seems reaching the 160 to 170° temp in the core of the piece will 'set' the pitch, and a fixed time to hold at that temp is not essential. Prolly feels better to hold the kiln temp for a period of time to insure that all the pieces in the kiln charge arrive at that temp, as well as the center core of every piece heats up too.
The kiln drying manual doesn't give a time period, nor does Joe Denig's pub on kiln drying. The two that I looked at. :)
-
sawdust, maybe the most important reason to set the pitch is so the wood can be sanded. Sanding creates heat, sap bleeds on the sandpaper, and sandpaper ruined. All in less than 15 seconds. And no, I don't know how to do it or how long it takes.
Dave, I’ve never been able to dry white oak without some surface checking. You can check the stuff within an hour if sawing on a clear day in the summer. It will surface out later in most cases. Follow Norms advice and you will be fine.
-
I Don't have any specifics, but, I picture "pitch setting" as I would a pot with half water and half alcohol. You might also think of it as distillation.
Water boils at 100°c. Ethyl Alcohol boils at around 78°c,
If you bring the temperature of the solution to 85° and then let it cool, you will have lost some water to evaporation(a surface phenomena) and some alcohol to vaporization (boiling throughout the liquid) You will still have both water and alcohol in the pot when it cools (other than what is lost by evaporation). It may still be inebriating.
If you bring the temperature of the pot to 85° and hold it there until there is no more boiling, the pot will not have anymore alcohol left in it, only water. It will no longer be inebriating. Granted, you will lose more water too, but it will be a lessor amount than if the solution was allowed to reach 100°c
This, in my opinion, equates somewhat to having "set the pitch" of the pot to 78°c. Returning the pot to this temperature will not allow alcohol to evaporate again. It is gone.
You can still get your hand wet though. There is still water in the pot.
To "set the pitch" of the pot to 100°c you need to raise the temperature to at least that, and hold it there until all of the water is vaporized. If you do that, the pot is now set at 100°c. you will no longer get your hand wet.
Raising the temperature of the pot above that temperature will no longer produce alcohol or water vapor. They are both gone.
-
I am sawing red oak for hay wagons and truck sides, which I started today. The shed is quite open, so I think it will get some airflow, I just don't know if it will be enough. Also, there is no electricity in the shed, so no fans. Anything that I sticker in there will be a byproduct of my current sawing project, so if I suffer a high degrade, I will have to accept it, I can't wait for cooler weather. I wish I had some white oak for trailer decking, but there is only one on the farm, and it's 8" DBH. ::)
Dave
-
One added note about the White Oak and shed drying.
The rot resistance and mold resistance of heart White Oak is very good.
If you saw the WO, now you could always err on the side of slower drying.
End seal the log as soon as its cut. Wrap the stack as soon as its built.
Cherry is another story. The sap wood will mold easily and quickly. Sugars!
On the other hand you don't have to "baby" Cherry very much in drying.
Please don't put Cherry in the same stack, unless it is on top and you don't
wrap that portion up.
Phil L.
-
BT, there's a good chance we are both right about this, from a practical standpoint. If you place a remote temp sensor in the center of the board, by the time it reaches the desired temp, the outer portions of the board would have Beenthere for quite some time, and any remaining volatiles would be trapped inside. :)
-
DanG, I think you are right....in spite of what FDH might think.. ;D ;D
-
:D :D :D