Drying Oregon white Oak

[Mike_Doolittle]

I took about 45 days to dry green 5/4 white oak down to about 7% in a Woodmizer (Nyle) DH system.  I got a small amount of mold growth on the front side but was wanting to go as slow as I could.  About 14 days into the load, I noticed some surface checking on the top boards only but they closed back up to never return.  I didn't get any end checking but about 10% of the boards wanted to warp from side to side.  I must add that almost all of this is vertical grain.  My question is, what can I do to reduce the amount of warp from side to side?  I don't seem to have much of a problem with this load of the boards laying flat.  Something else interesting is the amount of shrink difference even in different places in the board.  The white Oak around here has some wild grain and alot a character so maybe that is the issue.

[Curlywoods]

Mike,

  I am far from an expert, but it sounds like the logs that were cut might have had some amount of tension in them.  I have seen quarter sawn Oak and others bow like you have described, but it is not the norm, from my limited experience.  Maybe some of these pros can lend some sage advice on the matter for us all.

[jimF]

if you are getting mold you are drying at too high a humidity.  The high percentage of warp also supports this conclusion.

[Frank_Pender]

Mike, how long did you let it air dry before you placed it in the kiln.  I always let my Oak air dry for at least 90 to 120 days in the Winter months and 60 to 90 days in the Summer months.  Yes, you can easily get cupping, especially with boards wider than 6" at the 5/4 thickness.   Wider boards that are thicker, I have found much less cupping.  Location in the log, quarter, flat or rift sawn makes a great deal of difference as well, but the key for me has been the time sequesnce in air drying and the time in the kiln of 30 days and slow raising of the temp over that 30 day cycle.

[UrbanLogger]

In my experience, it is typical for QS (vertical grain) Oak to crook (warp sideways).

This is due to the higher density of the heartwood towards the center of the tree (one side of the board) and the lower density of the sapwood on the other side.

I typically trim off the sapwood during the process of sawing or before stacking to avoid this.   

[Mike_Doolittle]

Thanks for the input...all of you!
I'll try and answer some of your questions.  This is green wood and yes I know that air drying is nice but isn't always possible.  I have air dried some with worse results than what I have achieved putting green in the kiln.  One of you mentioned that warping sort of went along with the slow drying and mold growth on the front side of the process.  Can you better explain?  I understand the mold situation but how does slow drying or high RH cause warp?  It is hard to really tell but it seems to me that the warp starts later on in the process???  As far as the sap wood, I fully agree!  If you leave any of the white sap wood on a board, you are asking for trouble.
Thanks again all of you and keep the input coming.  I need to get this figured out because this is looking like it's going to be a major portion of my kiln business here in the valley of Oregon.
Mike

[jimF]

This is the reason wood warps more when it is dried slow. 
Below 30%MC as it losses moisture it shrinks.   When you dry fast there is a steep moiture gradient through the thickness.  With a steep moisture gradient only a small portion of the thickness is trying to shrink at any one moment.  The rest of the material is not and is resisting any movement of the board.  As the thin portion that is drying progressing towards the center both the wet center and strong dry surface will resist the movement of the portion trying to shrink.  No warpage can occur.
If you dry slow the shrinking protion is thick and is able to overcome the protions that are not shrinking and warp is able to occur.  The conditions for warp is setup early in drying but may become evident later on.
As for cutting of sap wood, there is no mechanical difference between the sapwood and heartwood and will not cause any additional warpage.  It does have chemical differences and is more suseptable to dacay.  The added chemicals in the heartwood can decrease the permeability of the heartwood and cause uneven drying between the heartwood and sapwood.
You have no control over what happens during air-drying and can be the most harsg drying conditions.  In the kiln you should be able to control the conditions to produce no damage.  It may be more expansive but you are able to control it.

[Mike_Doolittle]

Thanks Jim
Wow, this is deep.  I'm not real sure that I'm understanding so I'll try and put it into my words.  When the boards are above 30% MC I should continue to go slow but fast enough to not have mold growth and Min checking.  Once I reach 30% MC I should speed things up to min the warp.  Am I on track?
Mike

[jimF]

We are talking about two different things.  You are looking at average moisture content. I'm looking at the mositure content at each point of the thickness.  It is best to start drying fast from the start.

[Larry]

Few thoughts...not for sure if I’m right on couple of things so point out any error in my thinking.

• The only way for crook to occur in a QS board is one edge of the board has to shrink more than the other edge.
• The only way for the first to happen is the wood must be “different” from one edge to the other.

Most commonly crook occurs when one side of the board has juvenile wood.  Crook is toward the pith.

Couple forum members have been advocating sawing QS flitches to keep even tension on the board.  After the board drys they edge to remove the wane and juvenile wood (or pith).  I tried it and the method works, but...after the board is kiln dry and ready for use it will do crazy things when ripped on the table saw (pinching the blade, splitter, or spreading excessively).  I’m thinking there must be some residual tension left in the board.

I have been using another method when QS’ing a log.  Saw to minimize the amount of juvenile wood....after all it is normally low grade especially with oak.  Edge lightly on the sap side.  I’m still getting a little crook after the kiln, but they behave a lot better when ripped on the table saw later for cabinets.

I’m not for sure I am following Jim.  I guess Jim is saying to dry fast when below 30% MC as that is when shrinkage occurs along with the crook?  You sure couldn’t dry WO fast when above 30% in a DH kiln without degrade.

[jimF]

Larry,
Correct thinking.  What size flitches do you end up with?

[Mike_Doolittle]

I'm still not sure this is coming together for me, but the info is great.  I have been QS leaving no sap wood on any board and also making sure there is no pith left.
The bottom line is I guess to go slow down to 30%MC to minimize checking, then once the wood is down to 30% greatly speed up because this is when warping occures.  Am I correct?  What about temp affecting what is going on here?

Larry, I'm confused as to what you are calling younger wood.  I thought the pith was the heart and thus the older wood.  I thought the sap wood was the outside younger wood.  I guess I'm trying to be mature here and show how little I know but how eger I am to learn.
Mike

[Tom]

Mike,
It's really pretty easy once you understand what the parts are.

The pith is the growth bud on the top of the tree.  As the tree grows upward, it leaves this trail behind in the "chronological" center of the tree.  Notice that it isn't in the geometric center because of the affects of leaning trees and stuff like that.  The growth rings will vary in size from one side to the other, forming Tension or Reaction wood and the Pith will be off of geometric center.

The first 3 to 6 rings outside of the pith is usually considered to be "juvenile" wood.  The aren't very strong (relatively). They are avoided in turning because they will split.

Here is a document I found on Juvenile and mature wood.  I find it a little confusing but perhaps it will help.   http://www.for.gov.bc.ca/hre/syldemo/syl2juv.htm
another explanation:  http://www.forestprod.org/cdromdemo/jr/jr3.html

Then you find "heart wood".  Heart wood is composed of dead cells whose purpose is mainly to hold the tree up.  It was once a living part of the tree and carried nutrients to the crown but eventually succumbed to age.  It may still carry some fluids but is generally thought of as a passive material.  It includes the pith, juvenile wood and any rings that fit this description.

The "Sap Wood" lies on the outside of this.  It is the part of the tree that carries nutrients to the top of the tree.  It is usually more pliable than the heart wood and is actively involved in the growth of the tree.

The Cambium is next.  It is a thin layer of living cells that lies just below the bark.  It is where the cell division takes place and the girth of the tree is formed. The cells that lay on the inside form sapwood and the cells that lay on the outside create bark.   That's almost an over-simplification but still fairly accurate.

Here is one of my favorite links. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm
It isn't the kind of reading you will find on the science fiction shelf, but if you can stick to it for a few minutes, you will find it quite interesting and informative.  I continually go back to it for educational purposes and, believe it or not, entertainment.

If you are cutting out the pith and "all" of the sapwood on quartersawn stock, you might be losing a considerable amount of value.  Certain species have a higher value if the board is all heart, or all sap, but having both is many times acceptable and allows for the quarter sawing of smaller logs.

Don't be too quick to assign stead-fast rules in this industry, especially as a custom sawyer.  Beauty is in the eye of the beholder and the smaller your operation the closer you are to the end user.  that makes you to be closer to the definition of "artist" than to the definition of a production oriented sawyer.

[Larry]

Jim when QS’ing I want big logs so I can get as wide as possible.

Mike,
Definition out of Understanding Wood by Bruce Hoadley for juvenile wood..."Wood formed near the pith of the tree, often characterized by wide growth rings of lower density and abnormal properties.”

The italics are mind...abnormal is what causes the crook.

No idea what Oregon WO looks like but with our WO I can spot juvenile wood by color, rings, and texture.  Sometimes only one clue will be present.

I have been messing round with my mill and kiln for eleven years now and still learning.  Don't be shy about asking questions as that is how we all learn.

Here is one of my favorite links. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm
It isn't the kind of reading you will find on the science fiction shelf, but if you can stick to it for a few minutes, you will find it quite interesting and informative.  I continually go back to it for educational purposes and, believe it or not, entertainment.

Me to Tom.

[jimF]

I must be speaking in Brooklynese, I'll try it again in English.  Maybe I need to try to include some graphics - later.
"The bottom line is I guess to go slow down to 30%MC to minimize checking, then once the wood is down to 30% greatly speed up because this is when warping occures.  Am I correct?" No, before 30% average MC most of the shrinkage (warp) has already been set up.  Go as fast as it is safe from the very beginning. 
When we think of shrinkage we must talk about a specific microscopic point in the wood as far as what the moisture content is and if it will shrink.  The average moisture content tells us almost nothing.  The surface can be 10% and trying to shrinking while the average is 70%.
If the EMC is high causing slow drying, a thick portion of the thickness can be below 30% with the average being above 30%.  With the thick shrinking section, warp will occur.  Mold is an indication that drying is slow.
With fast drying mold will be halted, only a thin portion of the thickness will be trying to shrink while most of the thickness will not be shrinking and therefore resisting any warp. 
If it does not cause surface checks the drying is not too fast.  It is only when surface checks are occuring that drying is too fast.
While raising the temperature is one way to reduce the EMC and increase drying, this can have negative effects.  Another way to reduce the EMC is to decrease the absolute humidity.
For a starting point for what is safe, the Forest Products Lab publish schedules for each species.  While these are usually safe, some of them are slow and could safely be pushed faster with less degrade.  On their website I think you can download the list of schedules.

[Don_Lewis]

One of the biggest myths is that slow drying improves quality. Drying at the right speed is the better approach. Measure you daily moisture drop and try to hold it as close to 20% average or 2.6% on te fastest drying sample. This is covered in your manual. That stops mold and reduces deformation.

[Mike_Doolittle]

You guy's are outstanding to hang in there and beat it into my head.  I really appreciate your input and I think that I'm getting the concept.  This last load of Oak that I did, I notice some surface checking on my top boards so I got sort of cautious.  The interesting thing is that they went away to never return.  As we speak I'm making flooring out of about a third of it for a customer and it is turning out great.  I'm just trying to figure out the right combination so that I don't need to saw so oversized, if that makes any sense.
Thanks again!!!!
Mike

[jimF]

makes perfect sene.
I hope you realize the surface checks did not disappear or heal just closed up.

[Frank_Pender]

Mike, early on in my learing curve I thought the checking was gone as well, whoops no go away.   They will appear again in the planing process or just left to acclimate.   I know it takes time to let air dry.  Time, someone said is dollars.   With me I find that if the folks want the wood they will wait.  I would rathe have their friendship that a floor or building porject gone down the road with poor quality wood  and a floor constanting looking at someone that is not pleased, or a chest of drawers unable to be used due to cracked joints of large check points.