Maybe the best woodworking solution is a metalworking solution

[rslaback]

My dad was a woodworker all his life. Self-taught in most things after getting the basics from a grandpa that was a plywood knick knack shelf kind of guy. I learned from him growing up and spent countless hours on 4-H projects. I still enjoy it but haven't given it much time lately.

For my oldest sister's graduation in 1991 he built her a raised panel cedar chest. In doing so he learned hand carving and carved her initials into the lid. The chest is cedar lined red elm. He really liked the color of red elm even though it can be a pain to work with.

The top is a glued up panel with alternating grains but that didn't stop it from cupping. It's about 22 inches wide and has about a 5/16 swale in it. He put an apron around the bottom but that didn't stop it either. As the lid cupped and we kept sitting on it (it was under the dining room telephone) eventually the cup levered enough to rip out the back style.

My sister passed in 1994 and dad last December. The cedar chest now resides in my middle son's room and I've got a bug up my **** to fix it. I'm probably the hooligan that broke it after all. I have the back style back in place and secured mechanically as well as glued. I've scoured the internet to find solutions on how to unwarp the lid and came up pretty empty. Lots of crickets on web forum posts and a video here and there about manually manipulating the moisture to unwarp an in-progress panel. The best advice to unwarping a panel is to not. I really don't want to remake the lid, at least not yet. I am going to try stripping the top of the panel and using wet towels to warp the panel back to a semblance of flat. However, I am not naive enough to think it will stay that way.

I've wracked my brain trying to think of a way to keep it flat without looking nasty. The solution I have landed in is to hide a couple of steel stiffeners in the panel's apron. After all, I have metalworking skills too. I've incorporated slots for movement and spaced the slots to land strategically based on the panel seams. You can see where the apron was originally installed and the glue failed. It will need to be remade anyway as those pieces have been lost to the ether. The stiffeners are 3/8" so I am planning to make a canoe out of a piece of 3/4 to fit over top. To secure the thin ends I intend to rout a groove into the lid that the U should slide up into, hopefully keeping it in place and preventing it from opening up.

Wish me luck.

 

[logical]

I'm not sure I understand what you mean by "hiding the steel stiffeners". What apron are to referring to?

 

[bugzilla46310]

I have had some success bending pieces opposite the warp and clamping down for several days until they take a set. More of an art or trial and error process. Bend it too much and you can break the piece. Usually done this with unfinished raw wood.

 

[Firebrick43]

Most of the time curves like that are from uneven application of finish.

Most people finish the outside very well which limits the moisture absorption but don't apply nearly as many coats to the interior or bottom of a piece as its not seen. This bottom side absorbs more moisture because its not as well sealed and therefore the bottom side expands more and makes the piece curved.

A fellow that I went to church with took one of my arts and crafts tables that I built early on and bowed and placed it in his dehumidifying wood kiln when there wasn't a load in there. After a few days it was almost as straight as it originally was and I added some more coats of shellac to the bottom and it has staid that way since

 

[rslaback]

I'm not sure I understand what you mean by "hiding the steel stiffeners". What apron are to referring to?

If you look at the top in the background of one of the pics you can see the unfinished line where the apron had been glued. This illustration might help. In this picture the panel is red, the steel bar is blue and the hollowed out apron to be installed is white.

 

[rslaback]

Most of the time curves like that are from uneven application of finish.

Most people finish the outside very well which limits the moisture absorption but don't apply nearly as many coats to the interior or bottom of a piece as its not seen. This bottom side absorbs more moisture because its not as well sealed and therefore the bottom side expands more and makes the piece curved.

A fellow that I went to church with took one of my arts and crafts tables that I built early on and bowed and placed it in his dehumidifying wood kiln when there wasn't a load in there. After a few days it was almost as straight as it originally was and I added some more coats of shellac to the bottom and it has staid that way since

Could be. My working theory at this point though is that after gluing up the panel there were different amounts of passes on each side leaving the outside of the panel at a higher moisture content. When that dried it would cause this type of cup as well.

 

[MoonRise]

Beautiful piece.

Probably an uneven number/thickness of coats of finish difference between the top (concave) surface and the bottom (convex interior) surface. With the addition that the interior cedar lining probably added a small amount of moisture to the inside of the chest initially.

I would not run those steel bars on the lid, even with the nice slotting and chamfering that you did.

Wood moves. With temperature and moisture.

That lid probably did not warp overnight. Trying to straighten it in an afternoon is just asking to break something IMHO.

Temporarily adding moisture to the cupped exterior surface can certainly flatten the panel. Until the moisture evaporates or equalizes and the panel goes back to its current cupped condition.

If (big IF) the glue on the panel is fully waterproof, about the only way that I can think of to flatten the panel would be to steam bend it in a slightly opposite curve (to allow for spring back) and clamp it to a jig or bending form while the panel cools and dries from the steam bending. Rather risky IMNSHO.

Gently clean and refresh the finish or refinish the top (same number/thickness of coats on the top AND the bottom!). Wooden apron boards, slotted to allow for cross grain wood movement. Live with the slight cupping and tell the story to your family about how your Dad made the wooden chest for your sister and learned to hand carve the initials into the top and how over time the top cupped enough to rip some things apart on the chest.

A lesson in learning and skills and how something that we usually think is solid will still move. And how that movement can be strong enough to break things if there is no 'give' or way to accommodate that movement.

Maybe take your steel bars and make a steel chest or strongbox. To fit inside the wooden chest or as a separate piece.

 

[yhprum]

One option would be to cut all the laminated joints on all the glue joints, square up the edges and reglue it flat again.

 

[BigMike782]

I would kerf the underside to relieve the cup and then figure a way to dress the kerfs to look like they belong or remove some material and add some veneer.

 

[Axel207]

Looks like you’re on the right track with the metal bar idea. You may want to look at Blacktail Studio on YouTube, he’s done something similar by routing out a groove on the underside and setting in a steel channel for stiffening. He does a lot of tables from wide slabs with some crazy grain, to keep it from cupping.
Firebrick43 also has a good suggestion as well, that may be easier…

 

[niget2002]

I wouldn't bother trying to flatten it. I'd fix the box and then drill new holes for the hinges to where they line up now. I'd probably add a small wedge in each front and back corner so the lid rests on the wedges on the corners instead of wobbling.

Forcing the lid back mechanically could risk cracking it down the middle and ruining the hand carving.

Alternatively... Make a new lid. Then decide if you want to cut out and inlay the existing carving into the new lid. Maybe a nice heart shaped inlay with the existing carving in the middle of the new lid. Or, cut the carving out and turn it into a nice sign to mount on the wall above the box with a new lid.

 

[BigMike782]

Trying to force wood flat is a risky operation that you're likely going to lose.

 

[rslaback]

Trying to force wood flat is a risky operation that you're likely going to lose.

Forcing wood flat isn't much different than forcing wood to bend and we know how to do that fairly effectively. I really don't have much to lose by trying.

 

[HoosierBuddy]

I don't hate your steel idea.

I had a similar heirloom warp issue with a cherry, oak, and walnut chessboard I glued up in 8th grade shop class. I'm a long while out of the 8th grade! After decades it had warped more than what you're dealing with over a 30" X 30" board.

Nothing ventured....nothing gained.

I put a piece of cardboard on my garage floor then put the chess board "flat" on top of it, I put a piece of 3/4" plywood on top of that, then I jacked up the front driver's side wheel on my Ford Explorer, slid the whole assembly under the tire, and then lowered the tire down a bit at a time over a 24 hour period until 1/4 of the weight of a SUV was sitting on the board.

A day later when I took it back out from under the tire, about 80% of the bowing was out of the piece.

I prepared a piece of 3/4" plywood as a "backing", drilling and countersinking for perhaps 40 or so wood screws. I also built a 4" deep frame out of 3/4" hardwood using Kreg's pocket screws. I fastened the 3/4" plywood to the back of the board with the 40 or so wood screws, Set the board into the frame, got everything flat again (see very jank instructions regarding a Ford above) and screwed the frame to the plywood while the piece was held flat.

After that I cut a set of tapered legs for the framed chessboard assembly and made it into a table.

That was about 10 years ago. The board is still flat.

Did I get lucky? Sure....but with patience, you might get lucky too.

Your steel idea is kind of what I did with the frame. I just used a piece of plywood as a backing to help stiffen up the assembly before attaching it to a frame. Note, when I say frame, picture a 4-inch tall by 30 X 30 open box. The 3/4 plywood was cut 28 1/2" X 28 1/2. So, when I got done the assembly was about 5 1/2" tall and then got legs fastened inside the frame to make it into a table.