Lumber Cupping

[Keith Strong]

I am currently at the finishing stages of a project. While sanding the piece I noticed two boards starting to cup. I surfaced the lumber myself by removing a little material in three stages. Obviously the lumber was not properly dried. Is there anything I can do to get the lumber to cup the other way. Unfortunately there is snow on the ground so I can not do the grass/sun trick. Can I finish the concave side which will allow the convex side to dry and hopefully shrink? What about putting a fan or light on one side? Thanks for your help. You guys have bailed me out before.

[fRED mCnEILL]

I have straightened warped plywood by standing it upright in a small bathroom and using a fan/heater. Aim it at the convex side. The wood dries causing it to move.

[glenn bradley]

Certainly not what you want to hear but, I have pretty much given up on "salvaging" errant parts of a piece. I just make new ones and the ill-behaved parts become a smaller part of something else down the road. That's just me.

[Joe Shinall]

Keith I feel your pain. We have no lumber mills around here and I had a small keepsake box I just made for a friend's wedding present that I have to give them tomorrow. Had to buy red oak from the big orange borg.

The box is done and finished and tonight I just noticed the lid started to cup just a hair. Not really noticeable to anyone except a woodworker of course. But enough that if I had another week I would make a new lid. That's what I get for last minute project and making a lid of a solid board.

[Richard M. Wolfe]

The guy I work with in the shop just made a couple big (about 20"x24" and about an inch and a half thick) cutting boards and used alternating walnut and ash for contrast. He finished them and leaned them up against each other for a few days and when he laid them on a table each had a cup of a little over an eighth inch. He could afford the time and just set them aside three days ago with the convex side up. They are just about flat now.

I had the same thing happen with a wide but short ash board several years ago except it cupped about a quarter inch. It must really have been wet because it took flipping it about three times when the cup reversed itself. Works OK as long as you have the time to wait on it.

[David Thompson 27577]

{you told your story, then asked........}

Is there anything I can do to get the lumber to cup the other way.

{Then you said some more stuff.......}

Sorry Keith, but no, there is probably nothing you can do, short of re-milling the parts.

[george wilson]

We would WET THE CONVEX side of cupped wood. It seems wrong,I know,but when the wood dried,it would often make the board flat again. I even saw the furniture conservators do this to the tops of 18th.C. tables. They even placed a piece of plexiglass over the convex table top to make sure the water sank in deep before letting it dry out and pull the top back flat.

[Myk Rian]

We would WET THE CONVEX side of cupped wood. It seems wrong,I know,but when the wood dried,it would often make the board flat again.

Wetting the CONCAVE side >) has worked for me.

The box is done and finished and tonight I just noticed the lid started to cup just a hair. Not really noticeable to anyone except a woodworker of course. But enough that if I had another week I would make a new lid. That's what I get for last minute project and making a lid of a solid board.

That happened to me after finishing the dominos box I made for my Aunt.
After I finished a new top, the warped one straightened out on its own.

[Keith Strong]

I am going to start by putting a fan on one side of the wood. If by some chance I am able to get the wood to flatten. Once I apply a finish to all the sides, will this stabilize the wood or will the wood eventually go back to being cupped again?

[Howard Acheson]

Are these individual boards or boards in a panel or assembly? How wide are the boards? Are they in a position that air can get easily to both sides?

[Keith Strong]

Its a knock down bookshelf. The boards are 8" x40". I have them placed on the floor concave side down with the fan on top. Once assembled air will be able to circulate on all sides.

[Randy Dutkiewicz]

Keith I feel your pain. We have no lumber mills around here...

Ain't that the truth!!! I have to make special trips up to Atlanta to get some lumber. Sure wish someone would open a good lumber yard down here someday

[Randy Dutkiewicz]

[QUOTE=Joe Shinall;1574826]Keith I feel your pain. We have no lumber mills around here QUOTE]

Ain't that the truth!!! I have to make special trips up to Atlanta to get some lumber. Sure wish someone would open a good lumber yard down here someday

[Lee Schierer]

I'm a big fan of applying finish on all sides of pieces. I think it solves a number of movement issues. When wood dries it shrinks and if one side dries more or faster than the other you can get cupping. By wetting the short side (concave) or drying the long side (convex) you can sometimes straighten out a piece. Once it is flat, finish both sides equally as quickly as possible and most of the time it will stay put, but not always. Boxes are particularly problematic since one side of the lid is open to the room and the other side is isolated from the room. Again finishing both sides will help.

Cupping can also be caused if you glue the lid to side pieces that run across the grain. I've seen box tops curl up the side pieces because the lid couldn't move relative to the edge pieces.

[Rob Holcomb]

I've never had much luck with the wetting the wood method. It works good when you do it but after the wet side dries out, the boards just cup again. Wood will do what it wants. Now I just make a new piece or if that's not feasible, I live with it and call it "Character"