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post #1 of 23 (permalink) Old 02-09-2016, 09:29 AM Thread Starter
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Default Jerry's Most Recent Wonderment...

This query is in regard to minimized or eliminating wood movement.

I have been led to understand that the moement of wood is to due with moisture entering or leaving the tubular make up of wood at the end grain which causes a board to change it's dimension cross grain. If I need some correction in my understanding of this issue, please help me on that matter.

My question is this, and I'm sure that at least to some extent it has been discussed many times before, but here is the my question today, if the end grain is sealed so that moisture entering or leaving the board can be restricted how much can the lateral movement be reduced in terms of percentages if any?

The application that I'm concerned with is such. If one were to construct a panel that consists pf three boards in which the dimensions are 5" wide x 40" long x 3/4" thick and edge joined with splines, and the material is QS white oak, what would be difference the cross grain expansion or contraction difference between sealed and unsealed end grain.

The panel by the way would reside indoors in a relative constant environment temperature and humidy wise.

The reason that I'm thinking about this is that I would like to know to some degree the depth that the rabbets in the frame where the panel will reside and float in need to be to allow for movement.

I would like to keep the rabbet cuts at a minimum but not so tight that over the years a problem will not show up due to the cuts not being deep enough.

Now, in that the panel or panels that I am concerned with are for a cedar chest, all of my concern for movement may well be irrelevant
if the panels have strips of cedar glued to them in a cross grain fashion.

Some months back our late friend Dick Willis told me that the cedar iining, if installed as described with glue would prevent all or almost all movent.

Comments will be appreciated,

Jerry

P.S. Over the past seven months of my recovery from open heart surgery, you folks on this forum have not been plagued with my often wordy and sometime strange threads, but I'm getting well now so be prepared to put up with me again, I'm just an old guy that will turn 78 on the 20th of this month.

For all of you that have shown so much kindness and encouragement to me during my recovery, I am happy to tell you that I am really improving lately and boy does it feel good.
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post #2 of 23 (permalink) Old 02-09-2016, 10:21 AM
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Glad you are feeling better Jerry and god to see you posting again. Interesting question but I can't help you with that.

Bill
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post #3 of 23 (permalink) Old 02-09-2016, 10:25 AM
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Glad you doing so well Jerry. It's been boring without your provocation
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post #4 of 23 (permalink) Old 02-09-2016, 10:58 AM
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Good morning Jerry.

Although I haven't had the privilege of bantering with you before, I'm certainly glad to hear of your recovery.

To your question of sealing the end grain.

In your case, may I guess that the oak has probably been cut for awhile and is basically dry. Perhaps surprisingly, the end grain in your case is not likely to move appreciably differently than the centre of the boards.

What I always used end sealer for was when cutting lumber on my sawmill, and this was latex paint, the purpose for which was to slow down the drying of the end of the boards. Once dry, the boards would not have much seasonal movement. In this case if the ends are not sealed, splitting of the ends of the boards can be expected.

You mention glueing cedar across your oak panel. Do I gather that the cedar would cover 100% of the oak panel?

Two things come to mind here, the first being what kind of glue will you use? And secondly, I wonder if the end to end movement of cedar doesn't come very close to the expansion/contraction of oak across the grain.

If they are very close, then the panel will move very little. If the oak has more movement than the cedar, then the panel could bow very slightly on a seasonal basis. I doubt that would be much.

Essentially what you have there is a two ply version of plywood. So if one wood moved more than the other, some bending may happen. If you were to use thinner oak and then add two layers of cedar, you would now have a more stable panel I believe.

As for the depth of the rabbet, I would try something in the order of 5/16" to 3/8". You would want to avoid having it too tight for obvious reasons. A little loose would be OK.

I didn't check on the expansion rate of oak, but the cedars move quite appreciably. I think a lot of it is going to depend on the initial m/c of the oak.
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post #5 of 23 (permalink) Old 02-09-2016, 11:09 AM
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Think of a piece of plywood warping in all directions, the outer layers are moving in one direction and the inner layers are moving the opposite way .I am sure you have seen it many times.

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post #6 of 23 (permalink) Old 02-09-2016, 11:18 AM
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As Keith said Jerry, the primary reason boards get painted on the ends is slow the drying at the ends so that the board dries more evenly. Uneven drying causes stresses that result in cupping, bowing, and maybe to some extent twisting. Wood still absorbs moisture through the faces. QS grain orientation is one of the most stable orientations which is why it is preferred. Here is a page full of expansion charts but the few I quickly looked at didn't say if the rate was a percent or per inch of width but one of them will give the reference. https://www.google.ca/search?q=wood+...F9ecjwO0vaPACg
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post #7 of 23 (permalink) Old 02-09-2016, 11:40 AM
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Quote:
Originally Posted by Cherryville Chuck View Post
As Keith said Jerry, the primary reason boards get painted on the ends is slow the drying at the ends so that the board dries more evenly. Uneven drying causes stresses that result in cupping, bowing, and maybe to some extent twisting. Wood still absorbs moisture through the faces. QS grain orientation is one of the most stable orientations which is why it is preferred. Here is a page full of expansion charts but the few I quickly looked at didn't say if the rate was a percent or per inch of width but one of them will give the reference. https://www.google.ca/search?q=wood+...F9ecjwO0vaPACg
Thanks for that Charles. You guys are much better than I when it comes to tracking all this Google stuff down.

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post #8 of 23 (permalink) Old 02-09-2016, 12:05 PM Thread Starter
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O.K. guys, sounds like the best approach is to let the panel float free in the rabbets. The cedar lining would be attached only to the frame, but the issue of movement in project still exists, not in the floating panel but in the cedar lining and the frame.


I used a different design on my first try at a cedar chest two years ago and so far there is no noticeable issue due to wood movement. The learning curve is still going on.

I do appreciate the responsed that I have received and they are very enlightening, thank you.

Jerry
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post #9 of 23 (permalink) Old 02-09-2016, 12:18 PM
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Good to have you back Jerry. Glad you are on the mend. And don't worry about the wordiness of your questions. If you take the time to type them, I certainly don't mind reading them. Your questions tend to be interesting and thought provoking and are always welcomed by me.

Most of what I know about the subject I learned from books, not because I'm any expert. Here's what I've learned from much study:

Wood gains or loses moisture from every surface, but fastest through the end grain. When the wood is green, it has lots of moisture, and the end grain can give up its moisture much faster, resulting in a huge imbalance of moisture within the wood. This imbalance allows the ends to dry and shrink while the rest of the board is still wet, resulting in splits or checks at the ends. So, they seal the end grain to slow, not stop the release of moisture.

Wood will eventually gain or lose moisture to reach equilibrium with the ambient humidity. There's nothing you can do to stop that besides encase the entire board in plastic or something. All the surfaces of a board are capable of taking in or expelling moisture much faster than it can move THROUGH the wood to the surface. We need to slow down the surface exchange so that the entire board can keep pretty much the same moisture content instead of having wet and dry areas.

Now to your specific situation:
Rule of thumb for wood that will remain indoors is to allow 1/8" for each foot of width. You have a little more than 1 foot of width so allow about 5/32" to 3/16" for expansion.

I predict that any attempt to constrain wood from moving with humidity changes will end in disaster, especially with 15" wide panels. It will find a weak spot and split something somewhere. I know this one from bitter experience. Plan for movement and deal with it rather than trying to stop it. I would NOT glue the cedar cross-grain to the oak. Make some sort of frame to contain the cedar boards and allow them to float within the frame.

I hope this helps. Your mileage may vary . . . .
Free advice is worth what you pay for it . . . .
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post #10 of 23 (permalink) Old 02-09-2016, 12:34 PM
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Can't help you with the question but glad to see you are back and doing OK. I'll take this opportunity to wish you Happy birthday!

John T.
Life is like water-skiing; if you slow down, you go down.
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