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Author Topic: Lumber M/C ?  (Read 2486 times)

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Offline mrnero

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Lumber M/C ?
« on: November 10, 2009, 03:55:25 PM »
Just curious and this maybe a dumb question, I hear allot of the FF talk about kiln drying their lumber that you produce which I'm assuming is to lower the M/C. But what % of the M/C are you trying to archive from kiln drying and for what purpose ?  Thanks in advance.

Offline Tom

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Re: Lumber M/C ?
« Reply #1 on: November 10, 2009, 04:16:01 PM »
Mrnero.
I don't know if you are into numerology, or not, but sometimes it is fun to recognize when numbers match up for absolutely no reason.  :D

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Now, about kiln drying.

Kiln drying is a procedure, using a device (kiln), to lower the content of water held in the cells of lumber or timbers.

It's purpose is to 1. curtail rot, 2. add some stability and 3. kill insects and their eggs.

To kill the eggs (called Heat Treatment or HT), it requires that the center of the piece of wood reach a temperature of 130° F. for at least 30 minutes.  There is even a grading stamp that reflects that now.  Of course, the lumber must not be reinfected. It is only good to sterilize for those organisms that already exist.

The moisture content of a piece of lumber, or timber, is lowered to acceptable levels in a kiln 4. to hasten the lumber's trip to market. (thought I forgot one of them, didn't you)

Acceptable levels differ.  Most softwoods are dried to 19% because that is the level at which the wood is dry enough to begin taking pressurized treatment.

Some is dried to 12%-16% because that is the average humidity in the geographic area where it will be used.

Some is dried to 10% or less, because it is to be used inside of artificially controlled environments as cabinet wood, furniture or flooring.

It's the "change" in moisture content that causes warp, so creating a lumber piece that already has the average MC for the area is a goal.

Kiln drying in not necessarily better than air drying, just faster.

Some projects require air drying rather than kiln drying.  "Bending" is an example.  Most who build bent wood furniture would rather have air dried wood.

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Offline mrnero

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Re: Lumber M/C ?
« Reply #2 on: November 10, 2009, 04:28:30 PM »
Tom, Thats very interesting. I guess there is alot to know in preping lumber into its final stages. I'm going to keep your post for future reference. Thanks

Offline Tom

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Re: Lumber M/C ?
« Reply #3 on: November 10, 2009, 04:36:08 PM »
Ok!   There is a lot more to making good lumber than sawing squared strips of wood.   The first trap is thinking you know it all. Always keep an open mind and never stop learning.  There are miles and miles of sentences in The Forestry Forum that were carefully constructed by members to help describe "making lumber".  It's a good read.

Oh!  These numbers are also interesting and it won't look like you are counting until you've made quite a few more posts. :D :D

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Hmmmmm.  Isn't numerology fun stupid?   ;D
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Offline Den Socling

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Re: Lumber M/C ?
« Reply #4 on: November 10, 2009, 04:47:50 PM »
Tom missed one. MC is also a pain in the %&$@*. ;D I just got done unloading some monkeypod which may be 7% and the customer just called to say he changed his mind and wants 11-13%. Get out the hose?

Offline red oaks lumber

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Re: Lumber M/C ?
« Reply #5 on: November 10, 2009, 07:05:58 PM »
i kiln dry all hardwoods to 6%.  my softwoods 6%   pine 7-9%(4/4) drying down this far covers all applications
 wood being used outside doesn't have to be kiln dried
the experts think i do things wrong
 over 18 million b.f. processed and 7341 happy customers i disagree

Offline SwampDonkey

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Re: Lumber M/C ?
« Reply #6 on: November 11, 2009, 04:16:09 AM »
Hmmmmm.  Isn't numerology fun stupid?   ;D

Oh come on Tom, surely we need some math with those numbers. :D
Move'n on.

Offline stonebroke

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Re: Lumber M/C ?
« Reply #7 on: November 11, 2009, 08:26:08 AM »
Tom, isn't another reason to kiln dry is to set the pitch?

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Offline mrnero

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Re: Lumber M/C ?
« Reply #8 on: November 11, 2009, 09:41:44 AM »
Ok!   There is a lot more to making good lumber than sawing squared strips of wood.   The first trap is thinking you know it all. Always keep an open mind and never stop learning.  There are miles and miles of sentences in The Forestry Forum that were carefully constructed by members to help describe "making lumber".  It's a good read.

True, I figured that one out before, that you push the start button and then push the run button to begin in sawing square strips of wood. It seems that when I purchase K/D lumber products from lumber yards around here, its less complicated as to the % of M/C than what you are describing. In fact, I don't even think the % of M/C is even listed on the finished lumber at our retail lumber yards.
It must be interesting in how someone can kiln dry lumber to a low low M/C and then ship the product hundred of miles away and have the same M/C when it arrives at its final destination. They must be shipping in some sort of climate control trailers. Oh well !  enough on how to "making good lumber". Thanks
 

Offline Tom

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Re: Lumber M/C ?
« Reply #9 on: November 11, 2009, 10:53:28 AM »
The MC is usually a part of the grading stamp.  On almost all softwoods, like your 2x4 studs, the stamp will read kd19 or kd16.  The number is the %.

Yeah, I've always wondered how lumber could arrive at the retail outlet and be the same as when it left the kiln.  Short answer is that it usually doesn't.  The farther the lumber gets from the mill, the less expertise the handling and storage.  I read, one time, that a bundle of lumber will gain 1% a day until it equalizes.  I think I read that in the Wood Handbook.   Anyway, this article said that flat stacked lumber will gain water faster than it can release it, so the stack will actually become wet inside.

Now that's an interesting book to get into.  It's available as a PDF on the Internet and I read portions of it, now and again, just for intertainment.   They have formated the access page such that you can load the whole thing or just go to a chapter that interest you. :)

Yep, Stonebroke is right, kilns are used to set pitch too.  It takes an alternately heated kiln to do that though.  Solar kilns don't usually get hot enough, fast enough, long enough to satisfy most applications.

Setting pitch is a process where you try to keep the pitch from running out of lumber that will be used for presentation, like furniture or mouldings.   The idea is simple.  Pitch is made up of many different chemicals that become volatile at different temperatures.   That means that some of the chemicals might liquify and run if heated to 100° F.  So, they heat it in a kiln at 100° until the pitch quits running. That assures that the chemicals that will liquify at 100° have been boiled off, or changed.  You can then use that piece of wood as a floor, and it won't "bleed" as long as the temperature stays below 100°.  But if you use it as a window sill, it might reach 130°, and other chemicals will liquify (become volatile) and the pitch will "bleed" again. So that means that you need a piece of wood for that application where the pitch has been set at a higher temperature.  I think that the common temperature that mills try to reach, if they set pitch, is 160°.  Just reaching that temperature is not good enough though.  They have to hold it at that temperature untill all of the volatiles that liquify or gasify at that temperature, leave the wood. 

Our local expert and moderator of this topic, Dennis Socling, may make a better explanation.  He's a designer/builder of kilns and specializes in Vacuum kilns. 
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Offline Den Socling

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Re: Lumber M/C ?
« Reply #10 on: November 11, 2009, 11:45:41 AM »
Tom, you are doing a great job. Except for that numerology thing. :D

Offline JD350Cmark

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Re: Lumber M/C ?
« Reply #11 on: November 12, 2009, 10:14:49 AM »
Quote
It's purpose is to 1. curtail rot, 2. add some stability and 3. kill insects and their eggs.

Tom -  speaking of numbers, how'd ya do those little ones?   
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Offline Tom

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Re: Lumber M/C ?
« Reply #12 on: November 13, 2009, 02:26:19 PM »
The little ones are easy. 
Look above the smiley's and you will find icons that allow you to insert functions (put img banners around photo code), Create Hypertext (assign a short name to a long link), etc.

Those over the book smiley and embarrassed smiley allow you to raise or lower text in the line. Sup means to superscript and Sub means to subscript.  It lets you do things like indentify numbers in a list, or assign powers, like square 22 or cubed 33 and write chemical notation like H2O , NaHCO3 (in case you have a bellyache).  :D

There's lots of fun stuff above the create/modify/reply window that will help you to create an interesting post. 

You can change colors of type, use special characters, like: Degree°, copywrite©, microµ and even the old outmoded cent¢.

All you have to do to play with it is open a "reply" window  and type some stuff.  Then you highlight the word, character or phrase and click on one of the icons. 

Some are a little bit tricky, but still easy.  like making hypertext.   You start with a word like testhypertext.

Then you highlight it and click the "globe" icon.  What you end up with looks like this.

Code: [Select]
[url]testhypertext[/url]
Then you have to put an equal sign next to url.  It will look like this:
Code: [Select]
[url=]testhypertext[/url]
Then you put the address (url) of the website you want to go to, behind the equal sign.
Code: [Select]
[url=http://www.tomssaw.com/stuff.shtml]testhypertext[/url]
It will look like this when you make your post and people who click it will go to that address.
testhypertext


The "code" icon just allows you to banner other icons so that the code will show in a post instead of the programming taking effect.  If you use the "Quote" function at the top of the post (not the one in the icon list) the window that it opens will be what I've written and it will be bannered with quote icons.  That way you can see kinda how it works.


Those square brackets are used in bulletin board languages to simulate html code.  There are two that make a banner (because they banner the text).  The first one is a beginning banner and the second one (it contains a forward slash)is the ending banner. That tells the software the text that you want this function to effect.

You can play with this stuff all day by using the preveiw function at the bottom of the window instead of the post function.   A post is only made if you click the post button.

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Online Gary_C

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Re: Lumber M/C ?
« Reply #13 on: November 13, 2009, 03:19:51 PM »
That's a good explanation Tom. I was thinking that I should ask how to put a title on a web address instead of putting it separately. Also now I know and know what hypertext is.  8)

You should put that somewhere for reference.
Never take life seriously. Nobody gets out alive anyway.


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