drying of table rounds

[rebocardo]

I have cut a white oak tree up into table rounds. They range from 30-50 inches round and 3-4 inches thick. I have been using the end sealer from Bailey's to seal both sides and that has stopped the cracking.

These have to air dry. Do you think air drying them under cover or in a non-heated garage would take more then six months?

Should the bark be removed?

Once dry (I am getting a meter) should they be bought inside to equalize before planing off the end sealer and making the rounds even and sealing them with polyurethane?

[Den Socling]

I hate to sound pessimistic but they are going to crack wide open. I don't think there is any way of getting WO rounds dry short of the professor's idea of cutting pie wedges out and then gluing them back in.

It could take a whole lot longer than 6 months to air dry if you have them well sealed and the conditions are gentle.

I have had an idea for drying rounds but never tried it. If I tried rounds, I'd put some ass-kickin' sealer (some call it pin sealer) and not Anchorseal on the outer third of the ring. Make it dry from the inside of the round.

[Jeff]

They will crack. You're just slowing the inevitable.  There used to be a plaque factory in frederick Michigan that sliced off white pine to put various pictures of jesus, and the mackinaw bridge and deer and other stuff on. We could go there to gather fire wood when we camped on Otsego lake. They sold the cracked ones for 10 bucks a trunk load back then. They were always sliced on the bias and not cut into cookies. Sliced on the bias aparently gave them the ability to dry without cracking acording to the guys that worked there.

[rebocardo]

Do you think not sealing the inner 1/3 of the rings would work better?

Will kiln drying help or just be as bad?

My main goal is to sell them to people while still green since I do not have storage, but, I do not want to sell them if people are going to be greatly disappointed and they crack into a dozen pieces.

I think most people could live with 1 or 2 cracks. Plus, I do give people matching slices to fill in any cracks.
 

[Ianab]

The problem is that the wood dries and shrinks by different amounts in different directions. I believe Oak is about 7% Tangentially and 4 % Radially.  :P This means the diameter is shrunk by 4%, but the circumferance will shrink by 7%  :  Something has got to give.

One option is to cut from the bark to the pith in one place. Hopefully this will just open up a wedge with reasonably straight edges that can be filled with a matching wedge. Better than random and maybe multiple cracks.

Another option MAY be to cut out the pith in a circle, let the tyre shaped ring of wood dry and then fill it with a round plug. I'll leave it to someone else to figure out how to cut a round hole in a 4 inch slice ??? Maybe you could use my chainsaw, after an episode with a concrete fence post the other day it cuts good circles >:(  

Ian

[Ga_Boy]

Does the issue of cracking apply to Red Oak as well?

I looked at some Red Oak logs the other day that I wanted to cut into table rounds.  But if they are going to crack I won't waste my time sliceing them into rounds.

These are some BIG oaks.



Mark

[Ianab]

I dont know about red oak, but I think the cracking problem applies to about 90% of tree species. Some you can get away with if the difference in shrinkage amounts is not large and the wood is tough / cross linked grain that can resist the tension.

Another thing to try is what Jeff suggested and cutting them on about a 30 deg angle. You get an oval of wood and it will probably deform and warp a bit as it dries, but it has more of a chance of staying intact and the warp can then be machined off to leave a good slab.

Ian

[Jeff]

Yes, I would say it does apply. I have the proof in my shed. We cut a bunch of table rounds to use for the pig roast. I put some in the shed to try to slow the drying. These were cut from a log that was probably 5 to 6 years old from our log junk pile. They were not cracked when we cut them. The ones in the shed now have nice big cracks.

[Ianab]

To paraphrase Scotty from Star Trek "Yae cannae beat the laws of shrinkage laddie"

 :

[Jeff]

I rolled one out to show what I mean.

[jimF]

Someone at FPL years ago came up with the idea of a three step sequence.  I need to check it to be sure exactly the steps.  But I think it is to cover the center until the outer portion lightens up, then remove and dry slowly, then ???  the reason for the reverse thinking, is that the growth stresses are in compression on the edge so they can be reduce by slightly drying there first.  I'll check the exact proceedure.

[Jeff]

I suggest getting a package of sliced baloney. If you can figure out how to fry a piece without it cupping, you may be on to something.

[Tom]

Want to try something fun?   Fry a slice of baloney and watch it cup,  Turn it over and watch the cup develop inside of the old cup.  Turn it over again and break an egg in it and cover the pan.  The egg will "bake" and it makes a neat breakfast for kid or an old codger. :D

[Den Socling]

Aha! Tom tries to get us thinking about eating!  :D

There are a lot of dynamics involved. Shrinkage varies in different directions. But overall, sapwood cells are bigger, weaker and have more water than heartwood cells. So, they shrink more and and they shrink faster. That's why I've thought that some success could be had if the sapwood was sealed (thoroughly) while the heartwood was dried. But again, I never had time to try it. It was an idea I came up with when a guy wanted to dry rounds for a garden in Hawaii.

[Ga_Boy]

Tom,

Where do you put the grits ???.

As a growing young boy I gotta have ma grits. 8) 8) 8) 8) 8) 8)




Mark

[jimF]

Den, you may have used the wrong words accidently but.  Sapwood cells are not larger or weaker than heartwood cells.  Springwood cells in ring porous woods are larger and weaker than summerwood cells.  Nor do sapwood cells shrink more than heartwood cells - I'm a stickler for details. What the dynamics are, is that all cells shrink more around the trunk direction than through the trunk direction - I think someone else stated the same thing in other words earlier.
It seems that the outer portion starts to shrink first because it demonstrates a greater shrinkage than the center.  The only reason it demonstrates a larger shrinkage is that there is more material there to shrink than the center.
When a tree grows, it grows by creating two cells on the outside of the wood.  These two cells try to occupy almost the same size space as the cell they came from, causing a compressive stress in the outer wood.  These are called growth stresses.  These growth stresses can be used to your advantage during drying of disks.  This is also the reason why ends checks in disks don't start at the edge.
By covering the heartwood with paper or plastic, it allows for the outer wood to start to shrink and reduce the compressive growth stressses, thereby reducing all the stresses.
Once the growth stresses are reduced, the moisture content of the surface on the whole disk can then be reduced to avoid the development of mold.  
Once the surface moisture has been reduced, the whole disk can then be put in a bag with holes in it or wrapped in newspaper to cause the removal of water to be slow,  to keep the drying stresses low.

SUMMARY

phase 1, RH 60-70%, cover heartwood, avoid developing tension stresses in center and reduce growth stresses
phase 2, RH 70-80%, uncover the whole disk until surface lightens, remove the surface moisture to avoid mold
phase 3, RH 40%, put in a bag with holes, slowly remove remaining water to avoid high drying stresses.
originally developed by Hans Kubler

[Den Socling]

Hi Jim,
I'm not an expert and I agree that a cell in sapwood is not larger than a cell in heartwood. What I should have said was that the volume of water is larger in sapwood than heartwood. However, I believe that the extractives that change sapwood to heartwood have a number of influences including increased density. The sapwood, with lower density and higher moisture content would, in my opinion, be weaker and shrink more.
Den  

[Tom]

Member DonP once got into the science of cell structure in heart and  sapwood, old growth and second growth, for the purpose of determining movement and strength.  The thread is on the board somewhere and it is a good one.  I tried to follow it but it was over my head.  If you guys can find it, you would probably enjoy it.   I don't know if it would answer this particular question but some of thte same dynamics are envolved.  He was studying it for the sake of log or timber-frame construction.

[Jeff]

Wood Science 101?

Wood Science 202

[jimF]

Yes, the heartwood has a slightly lower capacity for water in some species than heartwood.  Species like maple have about the same extractive contents in the sapwood as the heartwood.  But where is this volume lost?  Most of it is in the cell lumen or center because the extractives take up space.  However, the water in the lumen does not effect strength or shrinkage.  Only the water in the cell wall.  Some extractives might enter the cell wall and effect the amount of water in the cell wall but to a very small extent.  When mechanical properties are tested, the presence of sapwood  or heartwood is not taken into account because the effect is insignificant.  What is effected to a large degree in some species is permeability, the ease  which water moves within the wood.  White oak is noted for this.  This would greatly effect drying stresses because a strong moisture gradient could be produced.  Since the amount of water is not effected and the amount of wood material is not changed from sapwood to heartwood, the strength is not effected and the amount of shrinkage is not also.  The reason for checks in round wood is that the degree of shrinkage around the trunk is almost twice that of shrinkage through the trunk.
 :P :P

[rebocardo]

So it sum it up, covering/coating the middle of the round (heartwood) and leaving the outside edges (sapwood) exposed will minimize cracking?

[jimF]

the center covering must be removed once the growth stresses have been nutralized.  Otherwise the tension drying stresses in the edge will become too great.

[Den Socling]

IMO Those tension drying stresses are going to be too great real quick. I hope somebody does some experimenting here but not with White Oak.

[beenthere]

jimF
Have you actually dried cross sections using this method?

If so, what species, diameter and thickness of 'disk' did you successfully eliminate (or reduce) radial drying checks?  

Sure sounds like, in theory, this method might work, although I will admit to being lost in the procedure as described. It sounds real subjective with a lot of seat-of-the-pants guestimation as to when the 'covers' (diapers?) need to be changed from the center location.

Some success stories would be encouraging, to say the least.

Do you have a resource of the Dr. Hans Kubler research where he presents the experimentation on this method of drying disks?  

Thanks

[jimF]

if you contact the Forest Product Laboratory in Madison WI they can send you the articles.  They are on the web