Reasons for difficult drying wood

[OakSavannah]

Trying to understand what makes a wood difficult to dry defect free.  I always thought T/R ratio had something to do with it. Take drying cookies for example. Oak is impossible to dry without cracking where I can air dry box elder cookies without a single crack yet they have the same T/R ratio.  Pine - can dry a load in a week where oak is 3 months and pine T/R ratio is almost 3.  So, it appears T/R ratio has nothing to do with drying defects.  What is it structurally that makes the difference? 

[doc henderson]

https://www.wood-database.com/wood-articles/dimensional-shrinkage/

sorry I had to first be familiar with the abbreviated term.

[beenthere]

Transverse and radial shrinkage differences still has/have something to do with it. But not the only thing.

Tell us more about your box elder experiences. I'd like to see the "no crack" in the cookies after drying. thanks

[OakSavannah]

These are some leftovers I did for a wedding 3 years ago. Cut green from a fence row in my corn field. I ran one of them through the planer just now for a better look.

[doc henderson]

I think some of it has to do with how easily water moves inside to out.  White oak is rot resistant and is harder to dry defect free due to its structure.  I think softer wood is more forgiving, even in the hardwood species like cottonwood. I know you may be drying lumber not cookies, but the cookie does represent those two dimensions well, and the longitudinal shrinking is considered negligible.  I also think with cookies the thickness vs diameter makes a difference.  the thickness of a cookie corelates to the "length of a log", and thicker has a longer attachment of grain side to side.  I have thought about graphing thickness and diameter of cookies to see if there is a formula that helps you know how thick will get best results vs diameter and species.  I do not have all the answers but thinking about the questions can help our understanding of related issues as you have brought up.

[jimF]

Yes, T/R shrinkage is a big factor as well as ease of moisture movement through the wood as a function of species as has been mentioned. Also the large rays in oak provides a weak point mechanically where the cracks start.

[NewYankeeSawmill]

I also think with cookies the thickness vs diameter makes a difference. 

I cannot get anything less than 2" thick to dry w/o cracking.
I've gotten a handful of request for 1" thick ones, think I'm going to have to saw on the mill @ 2", dry, then re-saw on a bandsaw after dried down.

[doc henderson]

smaller logs can make thinner cookies.  oak is nearly impossible.  the more difficult woods require more care.  talk with the wood turners that turn a bowl, then let is slowly dry in a box full of wood shavings.  I did 50 walnut cookies about 7/8th.  I did the denatured alcohol soak first then dried staggered apart (may have been the alcohol  ) in a box.   I went and alternated the staggering each day.  I have a 2 foot plus cottonwood that had been ignored in a container where I run the humidifier about once a month.  It is about 2.5 inches thick.

[doc henderson]

drying cookies and other weird stuff. (forestryforum.com)

[K-Guy]

All the prior information is good but sometimes it just comes down a log with internal stress you can't see. The slower you dry cookies the more chance they won't crack.

[jimF]

The principle behind the alcohol method that Doc mentions in the linked article is:the secondary chemical bonds the alcohol forms with the wood molecules are weaker than the bonds that the water forms with the wood molecules. So, after the alcohol is substituted for the water and starts to evaporate there are weaker stresses pulling the wood molecules together, thereby the wood is less prone to fail and form cracks.

There is another method of drying cookies developed by Hans Kubler. It involves covering the heartwood initially, followed by uncovering, then followed by putting it in a paper bag with holes. This initially reduces the stresses in the center where the cracks start, followed by removing the surface moisture to avoid mold  and ending up slowly drying to avoid high stress levels. He did alot of work in studying growth and drying stresses.