warped 1-piece back

**mandomaker** · Jan-30-2006, 12:04pm

Has anyone been mostly through carving a back plate (one-piece in my case)and noticed it taking on a warp? #My edges are lifting about a quarter inch on each side so it rocks around its longitudinal axis when one lays it on a table. #I am thinking of steaming or boiling it and clamping it to a level position and baking it for half an house at 150 degrees. #Is this a hare-brained idea? Will it probably split? #This can't be all that rare a problem. Can anyone offer help? #Thanks!

**Antlurz** · Jan-30-2006, 12:18pm

Have you had a drastic change in the weather since you started carving it?

Did you just get the wood from somewhere else in the world and start right in on it?

I'd let it set a few days and watch it. It very possibly could come back on it's own.

Ron

**amowry** · Jan-30-2006, 12:42pm

I've had that happen to some extent, especially with flatsawn backs. It's a result of internal stresses in the wood that can be there for various reasons. if it's slight and you are sure the wood is dry, it's not too big a deal, and the rimset will hold it flat. 1/4" sounds a little extreme, though. Maybe others can comment on your idea of flattening it.

**sunburst** · Jan-30-2006, 1:50pm

They "always" do that, especially flat sawn, and even if you took it off of a 100 year old mandolin and left it laying around. It'll clamp down when you glue it.

**Antlurz** · Jan-30-2006, 2:02pm

I thought the 1/4" sounded a bit extreme as well. John, wouldn't you say that a bit closer to half of that would be closer to what you'd expect...(depending on variables)

Ron

**sunburst** · Jan-30-2006, 4:05pm

I just checked all the carved, un-mounted-to-rim backs I have in the shop (3) to see how far from flat to a table they are. It turns out, they're all pretty flat. They're all quartered, and, though it doesn't really make any difference in terms of wood movement, two are one piece, and one is two piece. The only one that is close to 1/8" out of flat is an octave mandolion back that's over 13" wide.
I've had them move more than that, though, and though 1/4" would surprise me with quartered wood, I don't think it's extreme for flat sawn. When wood is carved as thin as a mandolin back, it doesn't hold still very well.

Mandomaker, if you put the back on a flat table top and press down on the edges, does it easily press down to the table? If so, I think it'll be just fine. You'll be stressing it a little, but it will conform when it's glued.

**Dale Ludewig** · Jan-30-2006, 6:48pm

As John said, I don't think a 1/4" is a problem if it presses down flat without much pressure. If you build as I do, and I think almost everyone else, the top goes on first, probably in a form, and the back will be fine. I wouldn't worry about it. Just my opinion based on experience. Wood moves.

**Ken** · Jan-30-2006, 7:41pm

Here is an excerpt from a long ago post by Spruce (I hope I'm not stepping across any lines here Bruce). I used this technique about a year ago and it worked like a charm.
Ken

"Cupping problems can be solved by using the same forces that created the cupping in the first place.

Wet the concave side and place wet side down on a wet towel, and the piece will invariable flatten out in a few hours...
Then, after it flattens out, lean the piece against a wall or hang it in the air so that both faces received equal air circulation.
It will usually remain flat..."

**sunburst** · Jan-30-2006, 7:59pm

Ken, that works well for billets and boards, I'm not sure I would do that with a carved back.
Sometimes carved plates do cup from lying on a flat surface so that both sides don't "breath" evenly. If there's a relative humidity change, it affects one side first, and more than the other side. Putting them on wire shelves, hanging them up, or something like that to expose both sides to the air equally can help prevent movement, and can even straighten them out if they do move.

**Stephen Perry** · Jan-30-2006, 9:27pm

You could clamp it flat for a while and see if the back likes it OK.

**Ken** · Jan-31-2006, 8:20am

John, I've only got the one experience of trying the wettng technique. It was on a mandola top with the outside carved and the inside just roughed out so it was still 3/8+ thick. I had to do it a couple times because I over compensated the first time and it curved in the reverse direction, but after getting the hang of it, it worked fine. Depending on the type of glue used for the center seam, I could see that wetting it could possibly become an issue.
Ken

**mandomaker** · Jan-31-2006, 1:34pm

I have not thinned the back down all the way-it's still a little thick-need to scoop out another.10" or so. It's pretty stiff and springy at this point and would definately want to lift up off the joint. On the other hand it should be more limber when I take out some more wood. I got some scrapers with a french curve shape and they are really helping me. I saw a mediocre The Gibson replica with a lumpy top and knew I didn't want that look. You could tell it was a bad knock-off from 5 feet.

**g_mc** · Jan-31-2006, 8:47pm

I'm always amazed at the timeliness of the threads on the cafe. Just last night I thought I would have to toss a doug fir top I had been working on for some time for being too warped ( my first attempt, no idea what I'm doing).
Anyways, with nothing to lose, tried the suggestion above (excerpt from spruce) this afternoon. Worked like a charm, the top is now almost dead on level. suh-weet!
Thanks cafe!