Round clock face from log end, finishing question.

[Jim_Rogers]

Recently, a young couple emailed me that they need a round log end for a clock face.

They wanted either red oak or cherry and 16" in diameter but only 1 or 2" thick.

I had just two weeks ago cut some round "cookie" shaped pieces for a fellow for table center pieces for his daughter's upcoming wedding. And I told them I could do it for sure.

Well they showed up yesterday and I just took a red oak log and cut off two cookies 2 1/2" thick and put them onto the sawmill and sliced them to exactly 2" thick with hopefully parallel faces.

They wanted suggestions of how to prevent them from cracking. I assured them that they would crack without question. But suggested that the seal them with anchorseal until just before the sign maker craved the face of the clock with his router sign making machine.

Does anyone have a method to treat or dry such a round clock face so that it won't split?

I told them of the method my friend used to treat some ironwood mallet heads by boiling the heads in some oil to push the water out and the oil in. An old timer told him of this method but that there was also another step beyond boiling the wood in oil but he couldn't remember the final or finishing step(s).

Has anyone heard of this?

Or know of a website where I can research this?

Thanks in advance.
Jim Rogers

PS. the ironwood mallet heads came out great, just boiling them in oil but they were only about 3 or 4" in diameter and about 6" or more in length. And of course a different kind of wood.

[beenthere]

Jim
You told them right....that they will split.

But I think I'd suggested they make a radial cut to the pith and use that as 12 oclock, then maybe some different length cuts to position 3, 6 and 9. Maybe shorter cuts for every 5 minutes. These cuts will relieve the shrinkage that will happen.

Then let the sign-maker person finish it off.   I'd a let it dry first.

[SwampDonkey]

Would Anchorseal help until you get the finish on, finish in multiple coats?

We used to epoxy cookies for display of rings, both faces and they would not split. Held in the moisture. Got to be careful to use UV resistant stuff I think or it yellows. It isn't totally coated so some tiny hairline cracks have appeared because of mositure movement.

**** I skimmed down through the posts the first time with out seeing your Anchorseal suggestion. ;)

A friend of mine did a clock from bald cypress root and it never split. That was 25 years ago. It's a crap shoot. Some woods will be far worst than others for splitting habit.

Some folks are transferring photos onto balsam poplar cookies and sealing with shellac (30 coats or so) and they don't split. Probably been Anchorsealed to.

[Ianab]

This stuff

http://www.rockler.com/product.cfm?page=686

PEG (Polyethylene Glycol). It's a heavy molecular weight stuff that replaces the moisture in the wood and stays in place. Because the wood never actually dries out, it never shrinks, so no splitting.

Basically you take your green Cookie, sink it in a tray of this stuff for a few weeks, and it's good to go.

Any sort of sealant can only slow down the drying process as it's all slightly permeable to water. This stuff works by replacing the water with something inert and permanent.

Ian

[kelLOGg]

On a much smaller (and thinner) scale, I have a friend who made coasters from cookies and to prevent splitting he boiled them in polyethylene glycol. It replaces water. It's available from woodworking stores and is $. I'd love to know if it works on your scale b/c I have had need of the same thing, too.
Bob

[kelLOGg]

Well, that's 2 votes for PEG. and within 27 seconds of each other.

[beenthere]

I know PEG. She... (nope)
Worked with it a lot in the 60's and lived through the many frustrations.

Because the cells are open in the red oak, there may be a slim chance that it will work.

If interested, my advice would be to first soak the green blanks (sections) in water for at least 3 weeks.  There needs to be max. water in the cell walls to exchange with the PEG. The PEG in the cell wall will bulk them up so they cannot shrink when the wood drys.  

Then immerse completely in a PEG solution of 50% water and PEG 1000 (by weight).  PEG 1000 is hard to find on the market. Shaved PEG sold by some is PEG 3000 and much more difficult to get into solution.

It helps to keep the solution warm, but warm solution also will start to grow mold. So mix a liberal amount of borax in to hold down the mold. From experience, on a one or two off'er, I'd suggest soaking for 5-8 months. Then remove and dry the blanks. Excess solution will drain off or can be washed off with very hot water.

I'd give the blanks about a 40 - 50 % chance of not cracking if these directions are followed.

If doing a larger production and rejects are not high risk that would mean termination of the project, short cuts (shorter soak times) could be taken.

If the PEG treatment is successful, then finishing the project is a major battle. Most finishes will not adhere to the PEG treated wood. Some 2-part epoxy finishes if thick enough will encapsulate the PEG (it is very hydroscopic at lower molecular weights and even PEG-1000 will bleed out of the wood with changes in relative humidity).  Very disappointing to have a finished wood project bleed PEG after a year or two.

Now, I really don't want to discourage anyone from trying, as the experience would be good for the soul. Success would be a bonus.
But PEG treatment isn't really what people would like it to be.

[woodsy]

I think you could try boring the pith out to keep it from splitting.  Once dry you would have to plug the hole.

A few years ago I was at a reclaimed wood outfit and they had several monster logs 3-4 feet in diameter and 40 feet long with the centers bored out the entire length to prevent the log from splitting to the center.  For the life me I can't remember what the timbers were originally used for but keeping them from splitting was crucial to their use. If it worked for those logs I don't see why it wouldn't work for a cookie.

[Jeff]

Its not the center that causes it to crack.  Experiment by frying a slice of baloney. Same physics involved. You can cut the center out, but the outside will still distort as it loses moisture as it fries. The only way to make it lay flat is to cut it so as the circumference shrinks it creates a gap. The crack you would see in a wood cookie as its cells lose moisture and its circumference shrinks.

[woodsy]

 A quick search on the internet will bring up this topic.  Apparently boring the center is indeed a technique that has been used by others to help prevent splitting.

Here is what Gene Wengert, arguably one the most notable gurus of wood, has to say on the topic;

"Why does a disk want to crack? Consider a green, circular disk that is 24" in diameter. As this disk dries, the circumference will want to shrink about 8%. So, the original circumference of (24 x pi =) 75.4" wants to shrink 8% down to 69.4". Of course, this cannot happen unless the diameter is reduced to 22.1" (that is, 22.1 x pi = 69.4 circumference). But, the bad news is that the diameter will naturally shrink only about 4% during drying. (Technically speaking, the circumference shrinkage is called tangential shrinkage. The radius shrinkage is called radial shrinkage.) So, the radial shrinkage is not enough to prevent the development of some substantial stress.

To avoid stress development and cracking, we have several options:

A fairly large hole could be cut in the center to allow the radius to shrink more.

Several disks could be cut and then one used for repairing the others. See archives here for more info.

A salt paste could be applied to restrict shrinkage

For thin, porous wood, the disk can be dried in alcohol.

The porous wood can be treated with a chemical that restricts swelling; PEG (polyethylene glycol 300 to 1000) is one such chemical, but it is expensive."

[SwampDonkey]

Yes radial shrinkage ( from pith to bark) in some species is about half that of tangential which is in circumference. Cutting a hole however won't increase radial shrinkage, the shrinkage % won't change. The hole will just grow bigger, not close in. The idea of a radial cut is to keep the stress localized so you don't get several checks around the cookie. It doesn't change how wood reacts to moisture changes. If you use something like hornbeam or birch it will dry more evenly in these directions and less prone to cracking. I was wondering if checking could be minimized further by cutting the cookies out of round, so they are oval. Seems to be the way some do it.

I challenge the good Dr.'s 8% figure (although I don't know the species he's referring). To get that type of dimensional shrinkage tangentially, you'd have to oven dry the piece. I think 2% to maybe 4% range is more real world, your only getting partial shrinkage, as some water is still retained because the wood equilibriates (is that a word? :D ) with the air. Shrinkage doesn't begin right away, only after the fibres lose bound water. Most of the water loss is free water.

[Jeff]

"A fairly large hole could be cut in the center to allow the radius to shrink more" is a much different statement then "boring the pith".

The tourist plaque shop in Frederick to the north used to cut them on a bias so they were oblong to defeat the cracking. We would go there and get trunk loads of the ones that did crack for our bon-fires while staying at the Otsego lake state park

[SwampDonkey]

Yes to what you've said Jeff, about the pith.

[Jim_Rogers]

I have passed on a link to this thread to the customer so that he can read all your advice about his project.

They have purchased some Pentacryl to try and prevent the splitting. Hopefully that will help them.

Thanks for everyone's input and advice.

Jim Rogers

[woodsy]

Please don't misread me here, I am not trying to be difficult, just wanting to learn as much as the next guy, so educate me. 

I understand the circumference shrinking, etc, etc in the cookie.  I get that.  But doesn't the center play a role in the cookie splitting?  If it doesn't, than why is sawn lumber containing the center of the log/pith prone to splitting and other drying defects?

For example, if we take a slab of wood 2 inches thick containing the center of the log, is it not reasonable to say that the slab will probably develope splits and have drying defects along where the center/pith is?

If that slab was cut into two pieces, thereby removing the center/pith, you would be greatly reducing the chances of drying defects.  So how does this differ from a cookie?  Can't you apply the same theory/basics to the cookie by removing let's say 3-4 inches of the center (from a 24 inch cookie) and by doing so wouldn't it at least help and lessen the chances of the cookie slitting through?   Am I missing something? 

Also, what technically classifies the pith as the pith? Is there a technical ending point or some sort of general accepted measurement within the diameter of any given tree that says this is where the pith ends? Or is it tree specific varying from tree to tree and is more defined by the dividing line between adult and juvenile wood?

Thank you, I appreciate the time taken to answer my questions.

[Tom]

The pith is year zero.  It is usually observed as a dark line in a board that is caused by the apical meristem as it adds cells to the top of the trunk or end of the limb, creating a new year's growth.  Picture the laying on of annual growth rings as if it were the dipping of a candle.






in a log or cookie, the wood dries faster around the circumference than through the middle.  when the wood on the outside dries, the circumference shrinks, but the wetter wood in the center of the cookie doesn't.  The wood is pulled apart because it can't squeeze the volume of the log or cookie into a smaller diameter.

A board that contains pith is stressed in two directions, both away from the pith on each side. Removing the pith allows the board to crook (bend to the side) as a result of this tension.  That is why the stability of quarter sawn lumber is a misnomer.  The tension that causes cup or warp is still there, only in a lateral direction.  Not including the pith in lumber decreases crook only if the stress is relieved. (that means edge trimming both sides.)

Juvenile wood is usually considered to be the first three to 5 years of wood laid down around the pith.  

The pith is composed of inferior wood, compared to the rest of the log and has little strength.

Juvenile wood also lacks strength, compared to mature wood. Here is a Gov. pamphlet that was probably lifted from the Wood Handbook.

Links to the Wood Handbook and other facts and interesting synopsis garnered from the Forestry Forum can be found in our Knowledge Base, the link of which is under Forum Extras in the top banner.

[SwampDonkey]

And juvenile wood usually follows the growth of the apical meristems. As the crown lifts the but of the tree puts on mature wood. This mature wood zone lifts with tree height growth.

[woodsy]

That is awesome Tom, thank you.

There was some confusion on my part as to what the pith actually is. I now understand what it is. I guess I have always had it in the back of my mind that the pith was basically all the junk wood in the center.  So, when I suggested that boring the pith out may help, I was actually thinking more along the lines of 3 or 4 inches or more and not just a wee little core.  Well whatever that's neither here nor there now.

Again, thank you for the explanation of drying and the pith; I really appreciate the time taken.   It all makes sense now.

[Magicman]

This red oak cookie was cut Nov 13th.  In less than a month it has split ¾".

[SwampDonkey]

It also looks to be a product of a lot of tension wood. 2/3rds of it's diameter was on one side of the tree's pith. ;)

[Magicman]

That was a "pasture edge" tree with all of the limbs on one side and with a serious lean.

It also was the "Limb Kickback" tree that I cut up into firewood.   :-\  I knew that any lumber sawed from that tree would have serious problems.

[SwampDonkey]

Well, good way to get even. Make heat out of the sucker. ;D

[Jim_Rogers]

Well a while ago, I asked about how to finish or preserve a log end cut for a clock face.

And I got all kinds of advice.

Thanks for everything that was posted.

Here is what they were hoping to do:



And another shot of the same thing:



The nice young couple who contacted me about this, sent me these two photos so that I could see what they were trying to do.

As a follow up, Friday, when I returned to my mother's house out in front of the sawmill yard, there was a basket on the back steps, which appeared to be a fruit basket dropped off by a delivery man.

I picked it up and took it into the house.

I started to open it and my mother, let into me about opening up her fruit basket that was left on her steps. I told her that the card in the basket said "thanks Jim" and that it was from two people but I wasn't sure exactly who these two people were. And the note said this is the results so far......

Well it wasn't a fruit basket, it had all kinds of cheeses, some crackers and several different types of smoked sausage which were very good I might add. And I was trying to figure out what these had to do with the "results so far"......

Then in the basket I found two photos:



And it then became clear to me that the names on the card were from the nice young couple that had purchased the clock face stock from me for their "gift" project.

I think they look good, or this one looks good.

And at first I thought that the line across the face of the clock was a crack.

But with closer examination here in the computer, I think it's a straight line recessed into the clock face, but I'm not totally sure.

I hope it's not a crack, and that their project has been completed and it will hand nicely in their friends home for many years.

We will see.....

Just an update to let you know what happened.

Happy new year to all....

Jim Rogers