Bowing wood after planing

[Andrew Seemann]

Remember it takes about 1 year for moisture changes to occur at a depth of 1 inch. So a 3/4" thick board would take several months to adjust completely to a new environment assuming both sides are exposed.

And the thing is, in most places, in several months, the relative humidity is different than what it was originally. Unless the wood is going into an environment with an unchanging moisture content (or it is exceptionally thin), it will never equalize to the ambient humidity, because ambient humidity changes before the wood can fully equalize to it.

For example, right now in my house, the relative humidity is around 25%, which is a little high for this time of year. In four months, it could be as high as 80% and even higher in 5-6 months. Last month when it was -30F outside it was probably close to 10%. Around here, wood is never quite the size and shape it really wants to be, so it is basically in constant movement.

[Bradley Gray]

Bradley, Robert and Jim are correct. In addition, never lay a piece of wood you have just milled equal amounts of each side flat on the work bench for more than a few minutes while you are working on it.

I don't think you read my posts

[Lee Schierer]

I don't think you read my posts

I did, but left out the words "except while actively working on it." I also stack and sticker my wood when it is in process or just being stored. It either gets weight or clamped.

[Jim Andrew]

I find that boards that bow after planing, often times will straighten after a few weeks. But not always. Years ago, I built cabinets in a house I was building, and used birch plywood for the doors. After the house was sold, and a guy moved in, a few of the plywood cabinet doors just went crazy. So I made some new ones, replaced the warped ones, and laid them down in the shop. Some time later, I noticed the plywood doors had straightened out.

[Don Jarvie]

Sometimes this happens and nothing you can do about it. If you can work with the bow then ok. Sometimes you need to mill another piece. Sounds like your process is good but just a bad board.

[Jim Becker]

I find that boards that bow after planing, often times will straighten after a few weeks. But not always.

Moisture related movement can tend to even out as things equalize. Tension related movement, well..."it's in the wood"...

[William Hodge]

I’m milling up wood for 6 trays i am making for friends and noticed that one of the boards bowed after I planed it flat. It sat for about a week after I had them all nicely squared and milled flat. How long do you folks wait before starting your projects? All the other boards stayed flat with no movement

Did you face the wood on a jointer before you planed it?

[Scott T Smith]

Remember it takes about 1 year for moisture changes to occur at a depth of 1 inch. So a 3/4" thick board would take several months to adjust completely to a new environment assuming both sides are exposed.

This is only partially correct.

The one year per inch rule" only applies to slow drying species such as oak.

Green 1" black walnut will reach equilibrium with it's environment in about 5 - 6 months, as well maple and several other species.

Green 1" poplar or pine will reach equilibrium with it's environment in about 3 months.

What also makes a difference is the time of the year. There is not much drying going on during the winter months in most of the USA, but the summer months are a different story.

The same holds true of MC% changes in a workshop.

Additionally, when moisture is regained by kiln dried lumber, it is regained as "free water" instead of "bound water". Free water moves much more quickly in and out of cells versus bound water (which is captured in the cell walls instead of in the middle of the cell). Thus kiln dried lumber that gains MC% will lose it more quickly than green lumber that is comprised of both bound and free water.

Kind regards.

Scott

[Bill Sutherland]

Yes it was faced.