Bowing wood after planing

[Bill Sutherland]

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

[Andrew Seemann]

Ideally, I use the wood right after planing, before it has a chance to move. The longer you wait after jointing and thicknessing, the more chance it has to move.

There are tidbits about letting the wood acclimate in your shop for x number of days before planing, taking the same amount off of each side, selecting certain grain patterns, and so forth; those help a little, but reality is that stuff will move after you mill it. You just have to take movement into account in your design: before, during, and after assembly. Nothing made of wood stays the same size and shape forever; wood always moves.

The reality is that I often don't get to mill the wood final length and width for days, weeks, sometimes months after thicknessing it. Additionally, the relative humidity changes so quickly and often here, that the wood never really reaches equilibrium; it is always a little behind. It is just something you have to take into account in your design.

[Matt Mattingley]

Any and all wood is reactional.

I just finished a cabinet with very tight clearances with natural wood sliders. Two months after installation they started to jam. The uprights we’re not moisture set, shrink and worped. Live and learn.

[Doug Dawson]

Ideally, I use the wood right after planing, before it has a chance to move. The longer you wait after jointing and thicknessing, the more chance it has to move.

There are tidbits about letting the wood acclimate in your shop for x number of days before planing, taking the same amount off of each side, selecting certain grain patterns, and so forth; those help a little, but reality is that stuff will move after you mill it. You just have to take movement into account in your design: before, during, and after assembly. Nothing made of wood stays the same size and shape forever; wood always moves.

All the cops have wooden legs, and the bulldogs all have rubber teeth, and the hens lay soft-boiled eggs, and warped wood can be surfaced straight.

This is why we don't buy deformed wood. You can only _reduce_ it's tendency to mess with you, and by then it's chopsticks. As the twig is bent...

[Bradley Gray]

When I have to let wood sit after planing I stack with stickers and clamp it on a flat bench. This keeps it flat and allows moisture to equalize.

[Doug Dawson]

When I have to let wood sit after planing I stack with stickers and clamp it on a flat bench. This keeps it flat and allows moisture to equalize.

But you can't take your eye off it and hope it stays straight, long after you release the clamps. Those tensions will always be there.

[Bradley Gray]

I am not clamping warped wood in an attempt to straighten it, I am clamping flat stock with stickers for air circulation so that uneven moisture exchange doesn't cause distortion. On a job that requires several days or weeks I clamp parts overnight at every stage until assembly and then I shoot finish ASAP.

I also make extra parts and reject anything that goes wild.

[Robert Engel]

What Bradley ^ said.

The key is keeping them in a controlled environment with minimal fluctuations in humidity.

I usually keep the stack covered with an extra board on top to keep the top board from drying unequally.

Especially with panels, I think "holding" a board with clamp or tape while acclimating is not a guarantee, but IME I feel it helps.

I have a climate controlled room inside my shop where I store lumber during milling.

That said, you're going to have the occasional board that misbehaves, which may be what happened here.

[Jim Becker]

There are a number of factors that cause this...internal stress in a given board and in-equal moisture content through the board. The latter can really come into play if you're not taking the same amount of material off both sides of a board as you surface it, including face jointing passes to flatten it prior to thicknessing. Sometimes that will work itself out through stickering for a period of time; sometimes it doesn't, especially when combined with internal stress. Wood is a natural material and can sometimes be unpredictable.

[Richard Coers]

Did you flat stack it after planing? A definite no-no. You need air flow all around wood after planing, especially if there is a weather and humidity change.

[Lee Schierer]

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 except while you are actively working on it.

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.

[Doug Dawson]

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.

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.

There's wood movement due to moisture adjustment, and wood movement due to internal tension adjustment. They are two different things. One has to judge which one it is, or in what proportion, and proceed accordingly. A moisture meter helps with this.

[Steve Jenkins]

I would bet that the board that warped was the top one on the stack. If you are going to flat stack them you need to cover with another piece of wood or a piece of plastic

[Bill Sutherland]

I did stack them and 3 stayed perfect and the 4th has about 1/16” bow in the middle. The board is 16” and 3/4”. I live in Eastern Wa (home of the ZAGS) and it has been cold. I do have heat in my garage shop when I’m working there.

[Doug Dawson]

I would bet that the board that warped was the top one on the stack. If you are going to flat stack them you need to cover with another piece of wood or a piece of plastic

I have lots of 50-pound bags of baking soda that hold down stickered wood very nicely. Recommended! Some people might suggest sandbags or cinderblocks, but those are hell on your tools.

(FWIW, I use them for abrasive blasting.)

[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.