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Warped 1 X 12 pine lumber

J

J. Schwiebert

Well-known Member
The kids in shop have some nice ! X 12 lumber. It has a slight cup to it. Any good ways to get the cup out? Thanks in advance. Boards are about 30 inch long and are to be used for shelves.
 
Turn the convex side of the cup toward the sun. Check it every few hours. Shouldn't take more than a day of two. Just depends on how bad the cup is.
 
Depends. If the wood was flat to begin with, then most likely one side has absorbed more moisture than the other and the wood fibers have swollen up. If, however, the tree was cut and milled with tension in the grain, then the only way to make it flat again (and stay that way) is to run it through a jointer and a planer. If your shelves don't need to be the full width of the boards, or if you don't mind a seam, you could also rip the boards down the middle. That will help them lay a little more flat. They will still be cupped, but to a less-noticeable degree.
 
Like kcm.MN said, they may have been stored in a damp location, turning them over and letting them dry may help.

But I doubt they will ever be completely flat.

If it's worth trying to save them, you could cut some length wise saw kerfs on the bottom, glue and clamp some cross braces to hold them flat.

Or rip them into strips, glue them back together, run through a planer.
 
I would put one under water for a couple weeks. Then sticker it with enough weight to straighten it. Leave it that way until good & dry. A year or so. If it works on one, it should do it on the rest.
 
Most of the time a cup warp is due to an imbalance in moisture content. The side with the crown has gotten more moisture than the cup side. This can sometimes be corrected by wetting the cup side and or drying the crown side. When you store lumber it's best to put sticks between the boards so air can circulate evenly. Sometimes you can cause a board to cup by laying it on a flat surface where air can only get to one side.
 
Ripping it in half then edge gluing it with the second piece flipped edge to edge. This will reduce the cup substantially. Running it through a planer or a Timesaver sander will make them flat and only 11/16 or so in thickness. Jim
 
(quoted from post at 17:32:26 04/02/17) The kids in shop have some nice ! X 12 lumber. It has a slight cup to it. Any good ways to get the cup out? Thanks in advance. Boards are about 30 inch long and are to be used for shelves.
Click to expand...

We were taught to rip wide boards and glue back together alternating grain for stability. There are two kinds of wide boards, those that are warped, and those that are going to warp....
 
If they are cupped from not being milled right at the saw mill, not much you can do except plane it back flat. If it is from moisture or not being dried right, then you need to stack it spaced apart and let it dry and then plane flat again if drying don't fix it. When planeing, take off just little at a time. If the press rollers of the planer press it flat, you wont accomplish anything. So just take off about 5 to 10 thousands at a time to avoid press roller flattening. And make the crowned side flat first, then the cupped side.
 
Eldon is correct. You should always rip wide boards down to 4 inches or less to remove stress and then glue back together. This is the only way you will permanently fix the issue you currently have.
 
We're talking "kids" and "shop" so I doubt if they have more than a few days, let alone a year. School lets out in June, and we're in April now.

So either plane the boards flat, or rip and alternate.
 
Since for shop project in school, cut in thirds flip middle board if you want joint edges, glue up then joint and plane. Will make for a better shelf than single wide board and good shop project at that. Good luck.
 
Just think of it this way. You can turn them with the low spot down in middle then small stuff won't roll off the shelf.
 
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