How can I straighten/flatten a large slice of burled redwood?

November 20, 2007 8:53 AM

At a flea market a while back I bought a pretty big (about 2'x4'x1.5") slice of burled redwood with the bark still attached. I'd like to turn this into a coffee table top, but it's warped. How do I straighten it?

Problem is, when I bought the piece it had been varnished on one side and left unfinished on the other. As a result, the entire piece is warped. So far I've used varnish remover to remove most of the varnish on the finished side. The bark is a bit torn up so I plan to saw the bark off and round the edges. Should I cut the bark off before flattening it? And what's the best method for flattening it?

I asked someone at a lumber yard and he recommended putting it outside in the sun for a day or so with a heavy object on top to do the major work and then sand it. Since it's winter, this option isn't gonna work. Is there any other method I can use on my own? At my disposal are a hand sander, jig saw and hand tools. Thanks!

posted by sub-culture to sports, hobbies, & recreation (15 comments total)

your lumberjack friend forgot to mention getting it wet. You don't need for it to be out in the sun, you can do this in your basement.

You might find a millwork shop with a planer big enough to handle it. Depending how warped it is, that might be enough so that you can skip the heavy object stuff.
posted by stupidsexyFlanders at 8:59 AM on November 20, 2007

You will not "flatten" it, not permanently, not that way. A major rule of woodworking is that the wood *will* move.

I would flatten it by planing it. Assuming you don't have access to a large enough power planer, you could do it by handplaning. This will reduce the thickness of course, depending on the degree of the warp.

You should probably let the wood acclimate a bit now that you've removed the varnish from the one side. Better yet, do a tentative planing first and then revisit it in a month to see if it needs fine-tuning.
posted by RikiTikiTavi at 9:00 AM on November 20, 2007

There's one major, straight, bend in the entire piece. So when I lay it upside down it see-saws on its center axis about an inch in either direction. I assume that that's a bit too much play to just plane it?

How much should I get it wet if I want to do it in my garage? Then, do I need to let it dry for some amount of time before planing it?
posted by sub-culture at 9:10 AM on November 20, 2007

Yes, that is too much play to just plane it. I'd say half a cup of water then tarp then heavy items on it. And yes, let dry for a couple days at least before planing.
posted by waraw at 9:20 AM on November 20, 2007

I think planing is being suggested as an alternative to wetting/bending. The warp will probably return after any kind of straightening you might attempt, but planing will give you a permanent flat surface. But since you have a warp that exceeds the thickness, the way you describe it, planing is probably out. I would consider: wet and weight, get it straightened out; then attach with screw and glue from the bottom a couple of lateral pieces of matching wood that will resist the warping tendency and keep it straight.
posted by beagle at 9:27 AM on November 20, 2007

Thanks. I thought that once the piece is straightened that applying varnish to both sides will prevent it from warping again since the one-sided varnish was (I thought) the cause of the warp in the first place. The idea of using lateral pieces to prevent additional warping is a great idea, thanks.
posted by sub-culture at 9:56 AM on November 20, 2007

Varnishing both sides won't guarantee that your wood won't rewarp. But then, neither is planing a guarantee of stability, either. And the lateral pieces you are considering also will not guarantee permanent stability. Wood moves, like it or not. My suggestion would be to do a minimal planing (perhaps leaving some irregularity) and base your coffee table around the wood's imperfections, which includes that it will never be perfectly level.

Consider how this bench exposes and makes use of "imperfections" to good effect. Is there a similar way you can make emphasize the bend in the wood to create a really unique piece?
posted by Forktine at 10:45 AM on November 20, 2007

The varnish will slow down moisture exchange between the wood and the atmosphere, but it won't stop it altogether.

I don't think I would GLUE the lateral supports to the tabletop; this thing is gonna move, eventually. Don't fight it. A stiff glue joint, across the grain*, can result in splits. Screws alone (in elongated holes) should be stiff enough to keep everything flat while providing enough room for the top to expand and contract.

-------------------
*Never having worked with burl, I have no idea how what direction the stuff actually moves...
posted by notyou at 10:54 AM on November 20, 2007

That bench linked by Forktine looks to be perfectly flat, but his suggestion of working with the imperfections does suggest another approach: rather than making a coffeetable, make a bench, and leave it warped, just as a comfortable chair would have some curve in the bottom.
posted by beagle at 11:18 AM on November 20, 2007

It's very unlikely that wetting it down or putting weight on it will have any lasting effect, and it's certain that wetting it down will complicate the problem. You need to:

1) Let the plank acclimate to a normal, presumably heated, indoor environment. Lean it in a corner for at least a couple of weeks.

2) Flatten it by making it thinner. Best tool for the job is a wide-belt sander, if you're lucky enough to find a millwork or custom cabinet shop that owns one. Failing that, a large surface planer followed by some hand sanding. Hand planes are great if they're sharp and well-tuned, but I'm doubtful you have that option.

3) Finish both sides similarly.

4) Fasten it to whatever base you use in such a way that it can grow and shrink across its width without splitting itself or pushing the base apart. Redwood is quite stable, fortunately. A varnished plank 2' wide should only grow and shrink about 1/16" of an inch between summer and winter, though it could move considerably more if left unfinished.
posted by jon1270 at 1:27 PM on November 20, 2007

If you remove the bark carefully, you may get that nice curve of wood just below the bark, which would be a very nice edge.
posted by theora55 at 3:14 PM on November 20, 2007

Here is an article you may find helpful:

http://aic.stanford.edu/sg/wag/1995/WAG_95_howlett.pdf
posted by bluebird at 3:31 PM on November 20, 2007 [1 favorite]

I read in an old book that the way to get warped wood back to its original ( presumed flat) shape was to merely lay it in grass for a week or two. The wood will absorb moisture from the grass and revert to form.

Or just flop it on a huge tabletop belt sander till flat, find a mill that will do a side for you.
posted by Max Power at 3:52 PM on November 20, 2007

Bluebird's link is awesome, the other way to permanently flatten is to steam and press the wood. The heat and moisture of the steam will actually free up the natural glue in the wood enough to permanently deform it. As it cools it will reset into something close to the new shape. You'll still need to plane it, but less so.

Any of the other methods mentioned will be reversed in time unless you rigidly attach the wood to a very straight and sturdy frame. Even so, the piece will be under constant tension. IANAC.
posted by BrotherCaine at 4:10 PM on November 20, 2007

Steam bending FAQ.
posted by BrotherCaine at 4:11 PM on November 20, 2007