Question about thin woods and cupping

Hi Douglas;

Thin boards can be a pain in the neck, regarding warpage. The reason the boards are cupping is the moisture content is changing on the inside of the cup at a faster rate than the outside. The wood shrinks as the moisture evaporates, and if it is not equal, the drier side will curl up, and form a cup.

One solution, which we use is to dampen the inside, or dry side of the curve. Done carefully, and stickered, maybe even covered with a plastic bag, then left to aclimate to the moisture you have added, should remove the cupping. As I mentioned, do this carefully,and allow seneral days between dampening and drying to check your progress. This is so you don’t end up moving the cup to the other side of the board.

Another option is to rip the board into narrower sections. You the can alternate the annular rings, which will make it more stable, but will interrupt the grain pattern. My preference in this method is to keep the pieces positioned as they were, but it seems to make a big difference in the sability if you rip them and glue them back to gether in the same exact order as they were. The glue joint is fairly difficult to detect, as the grain is not interrupted, and the board tends to act as narrower pieces, rather than one wide piece.

Hope this helps you out.

Lee

-- by Lee A. Jesberger http://www.prowoodworkingtips.com http://www.ezee-feed.com

I’ve never tried as Lee has said with the moisture but I’d done the latter. Ripping into narrower strips Putting on a 90 deg edge and then re-gluing. You will probably need to flatten again but just a little.

-- Karson Southern Delaware karson_morrison@bigfoot.com

Great topic, Doug. I’ve had the same question.

Lee, your first approach sounds pretty good if a person really needs to keep the grain integrity (even though the seams would be hard to see).

-- Jeff, St. Paul, MN

After seeing the FWW piece on double steam bending, it just made me wonder if I could throw it in the microwave with a wet towel and then clamp it between MDF with cauls, etc. But the wood has all been kiln dried, so the lignin bonds are set. I’m going to try the moisture thing though.

-- "Bordnerizing" perfectly good lumber for over a decade.

Hi Douglas;
—-something along the lines of what Lee has mentioned up there in his comment I have also done, with some success.

Not so much in the area of small thin boards, but with wide boards….24’’-30’’ wide and such x 1’’ and greater in thickness….

I will place the cupped side, face down in the grass of an early morning dew and then watch the wood as the sun starts hitting the wood, when the wood starts to straighten out, I have then taken it inside and weighted it down with concrete blocks for a few days.

Your wood is smaller and thinner, but this might work out great for you….?

Thank you.
GODSPEED,
Fraank

-- --frank, NH, http://frank.wordpress.com/

And I can suntan my cherry at the same time. Thanks, Frank. I always appreciate the way you connect to the world.

-- "Bordnerizing" perfectly good lumber for over a decade.