Curly maple table top cupping problem

[Tom Larson]

I am building a curly maple, Queen Ann low boy. And things went well untill I glued the top together .....At first it looked great , In fact for about a week . Then it warped , then it flattened out , then it warped again ,and has kept doing that for the last 3 months. Iam guessing that it is humidity but shouldn't it quit at some point? The wood was pretty expensive so I would rather not throw it away. Does anybody have a sugestion?

[Matt Ocel]

Tom -

I am interested in what people have to say.

I just jointed, planed, and glued up a 2 year old black walnut into a table top. 4 pieces 5 1/2" wide x 30" long.
It was perfectly flat for a week, then cupped, I turned it over and it flattened out, then cupped again.

[Chris Padilla]

Tom,

Tell us about what you did to glue up the top...like Matt did.

Wood: a fickle medium!

[Peter Quinn]

Uh..maple...she ain't the most stable breed in the stable! I've made stair treads from maple and they seem to keep moving hour by hour for months till you screw them down. Same thing with counter tops (non laminated) Its almost comical. A stair tread is basically a small table top, though its end may be less glorious. I've tried stickering them, stacking them tight and wrapping the ends, flipping them, sealing the ends with shellac...to no avail.

I am not of the opinion that a table top needs to be perfectly flat or that you can expect it to stay that way over its life time. Certainly there are limits to what you can accept, but once the top is secured to the base and trimmed with a molding will the amount of warping you have experienced be a problem?

I don't have experience with curly maple specifically, but I don't generally expect maple to be perfectly very stable, and I don't expect figured wood to be as stable as more common examples of the same species.

[Ted Jay]

If you were to glue up narrower pieces in the first place, by ripping 5 1/2" boards down the middle, then plane and joint them before gluing them up. Would that alleviate or minimize the cupping to be not as noticiable?

[Don Kondra]

It was perfectly flat for a week, then cupped, I turned it over and it flattened out, then cupped again.

This may be the cause of the problem.

First lets assume the wood is dry and has been acclimatized to the shop.

Nit picking but if possible I try to joint and plane the same amount off each side of the boards.

Then after the lamination is dry and taken out of the clamps, I store it in such a way as to allow air movement on both sides.

Normally I lean my tops against a wall, long time ago I found stickering to be less than effective.

Hope this helps,

Cheers, Don

[Frank Drew]

Wood: a fickle medium!


Boy, ain't that the truth!

And I agree with Peter that maple can move on you (and maybe because of its hardness is perhaps more prone to glue joint failure than a lot of other woods we use.

I had this same unhappy occurence with a birds-eye maple table top that didn't get the same amount of finish top and bottom and I think that allowed the underside to absorb marginally more moisure, thus cupping. That, plus the fact that it spent its first couple of years in a flower shop under a sheet of glass, effectively sealing the top, but not the underside.

[David DeCristoforo]

Is the top attached to the piece? If it's hanging around loose and unfinished, it's going have "free reign" to move around. Once it's sealed and attached to the base, it should be fine. Unless you have already done that and it's still warping. Hard to tell from the post....

[Tom Larson]

Well... I ripped the wood into 5.5 in. pieces , jointed them & planed them to the approx. thickness. No bisquets - Tite Bond ll glue - clamped over night, then I scraped it flat and let it set for a week or so. When I got back to it the wood had warped as I explained earlier. The top was fastened down for a while but I thought if I removed it & stood it on end where the air could get to all surfaces ... didnt help. As far as it being enough to worry about, the warpage gets up to .5 in. at times on a 32x20 inch top . I had thought about cutting "reliefs" on the back side of the top like you see on decking material. Any ideas on that???? Thanks for your replys and I am looking forward to hear more from all of you.

TOM

[Bill Wyko]

One way to reduce this problem is to look at the end grain and flip every other plank so the grains are opposite before glue up. This way it'll cancel out the stress. I'm not sure what you can do now. Possibly a piece of veneer on one side to make it pull. That's just a guess though. Good luck.

[David DeCristoforo]

"When I got back to it the wood had warped...The top was fastened down for a while...warpage gets up to .5 in..."

OK. But can you push the top flat with your hand? If you can, you will be able to pull the top down flat when you attach it to the base.

Also, you can try this: Moisten the concave side of the top. Let it sit for a while but keep the concave side moist (not wet...a "spray bottle" set to a fine mist will work fine for this.) As the concave side absorbs moisture, it will expand and the top should flatten out or maybe even bow slightly the "other way". Then let it dry and as soon as it's dry to the touch, seal both sides and ends. Then attach it to your base or to a temporary frame to keep it flat.

[Curt Taylor]

I agree with Bill insofar as the direction of the growth rings being a problem. If they are all running the same direction, the tabletop will want to conform back to the shape of the tree. Also double check the moisture content of the wood. For the price of the wood involved and assuming the direction of glue up is the problem I'd be inclined to rip it back down, along the glue lines, joint them again and do another glue up alternating the growth pattern. Also, assuming the moisture content is at 6 to 8 percent I'd suggest sanding and getting a finish on all sides the day after glue up.

[David DeCristoforo]

"If they are all running the same direction, the tabletop will want to conform back to the shape of the tree....etc."

Actually, there are two "schools of thought" when it comes to grain orientation in glued up panels. One is as you describe, flipping every other piece to "average out" the tendency of the boards to cup. The other is as the OP has done which is to orient all of the boards in the same direction so that the cupping becomes a gentle curve over the entire width of the panel which is, typically, easier to pull flat by attachment to a rigid frame, capturing within a frame (as in a door) or by "breadboarding" the ends. Both concepts have their advantages and drawbacks. One of the downsides of flipping every other piece is that with some woods (figured maple is at the top of this category) light is reflected differently on the opposite faces resulting in almost striped appearance. So the desired final result should be a factor in the way that grain is oriented. It's not "cut and dried" (no pun intended).

[Cliff Rohrabacher]

Sounds to me like it's absorbing moisture in the evening and losing it in the day and responding to each.
When you leave the shop at night cover your work.

[Eddie Darby]

Have you kept track of the humidity levels in your shop during all this movement?

[Dave Norris]

Does the whole thing cup as a unit, or is there a particularly offensive piece? Do you know the moisture content of the board off hand?