Rapidly Curled Oak

[John McKissick]

White oak stair tread glued up commercially I have had for over a decade stored in unheated with marginal humidity controlled shelter. Air was available to all sides of the board(s)

yesterday I planed out a noticeable but not severe cupping (1/16") with planer/planer sled and got it pretty darn flat. Crosscut out a 10"x8" section and brought indoors to run on CNC.

Today, one day later, it's extremely cupped and warped well over 1/8". My planer cuts were not heavy cuts at all. Deliberately took smaller light cuts

What happened? Stress or humidity?

[Andrew Seemann]

How long has it been indoors? If not long, chances are the indoor RH is lower than where it was stored before and it is "equalizing"; that is, changing shape.

[Andrew Hughes]

Did you plane fairly equal amounts from both sides. Its either stress that's been there from the beginning or moisture. Sometimes milling something 2 or 3 times really helps.

[Lee Schierer]

Moisture content. Wood kept in the conditions you describe will gain moisture over time. Bringing it into your shop and immediately removing material will almost always result in the piece cupping. Lay the piece concave face down on the floor or work bench and it will likely flatten out. Once it is flat store it so it gets air circulation on all surfaces. Stickering and weigh down is preferable. Don't do any work on it for a couple of months.

[Richard Coers]

It could take 1-2 weeks to fully acclimate if your shop is really dry. My furnace has been running a lot, humidity rapidly dropping in the shop.

[John McKissick]

How long has it been indoors? If not long, chances are the indoor RH is lower than where it was stored before and it is "equalizing"; that is, changing shape.

About 24 hours now. Drier indoors of course

[John McKissick]

Did you plane fairly equal amounts from both sides. Its either stress that's been there from the beginning or moisture. Sometimes milling something 2 or 3 times really helps.

Pretty close to equal amounts in pretty shallow cuts. First 5-8 passes of light cuts I had it hot glued to a sled till flat then removed from sled and passed through another 6-8 times on a MDF stationary sled, again all light passes.

[John McKissick]

Moisture content. Wood kept in the conditions you describe will gain moisture over time. Bringing it into your shop and immediately removing material will almost always result in the piece cupping. Lay the piece concave face down on the floor or work bench and it will likely flatten out. Once it is flat store it so it gets air circulation on all surfaces. Stickering and weigh down is preferable. Don't do any work on it for a couple of months.

I am familiar, far from an expert, in what you describe but to see that much curl over night just flabbergasted me. Means I am pretty much shut down for the winter for any CNC work. All my my wood is in outdoor temps with limited humidity control.
Disappointing

[Andrew Seemann]

About 24 hours now. Drier indoors of course

That likely is the culprit. Bring what you can into the shop, or squirrel it away in the house somewhere for a couple weeks, and give it a try again. I don't necessarily season my wood for months in the shop, and I would be amazed if every commercial shop in my area does as well. Even if you leave it for a month, it will probably move a little after milling. Best to use it right away while it is still flat.

I need to do a 4' x 7 ' table top soon, and I am not gluing it up until I know I can bring it to be run through a timesaver the next day.

[John McKissick]

Update- After letting the above mentioned small chunk of oak get air on both sides over the second night most of the distortion was gone but still not flat enough for CNC. I set the part up convex surface up, supported on the edges with a small weight on it. I'll let it acclimate for a few weeks checking periodically.

I brought inside a few other chunks I planed the same day and let it sit overnight with spacers to allow airflow on both sides and those stayed flat over ONE night.

So I think I isolated the issue to differential drying indoors. I was very surprised to see so much movement over such a short period of time.

So now my plans are to guess what material I will need and let it acclimate for a few weeks prior to planing or machining. I have quite a bit of oak, cherry and other stuff needing milling before using

[Tom Bender]

I'm guessing the first night it was flat on your bench so it dried on only one side.