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Last week, I doweled and edge glued 5 pieces of red oak . after clamping and weighting, the 18" x 24' piece was nice and flat. I left it in my moderately damp basement workshop, and today i found it to have developed a 1/4' bow across the edges. i dampened the piece and clamped it to a steel saw table. What can I do to prevent it from warping in the future? I heard that using boiled linseed oil on the unfinished wood might work. Would appreciate any advice. Thanks ! tomconn42
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06-21-2017, 12:25 PM
(This post was last modified: 06-21-2017, 12:26 PM by JGrout.)
Probably the best thing you can do is alternate the annular rings in the glue up and stop using dowels you do not need.
The issue with wood is it is going to move and you can only work with the material to reduce the way it moves.
I also question the validity of weighting the piece in the manner described, that leads me to believe your edges are not perpendicular to the faces or you are not alternating clamps top and bottom and checking the glue up with a straightedge in several spots
Joe
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The key is:
1) start with acclimated wood
2) store in a steady state climate.
Other factors that cause uneven exposure like not using stickers, having a fan or light over the panel, etc.
You might try storing the panel vertically next time.
I no longer worry about alternating annular rings because:
1) I'm more concerned about grain matching/direction
2) I don't think it matters.
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(06-21-2017, 01:06 PM)rwe2156 Wrote: The key is:
1) start with acclimated wood
2) store in a steady state climate.
Other factors that cause uneven exposure like not using stickers, having a fan or light over the panel, etc.
You might try storing the panel vertically next time.
I no longer worry about alternating annular rings because:
1) I'm more concerned about grain matching/direction
2) I don't think it matters.
your two key points matter in this case
I get the matching grain etc and that is fine but we have no idea how other than his climate the stock was cared for the MC if it was KD or left in a haphazard pile somewhere
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If the cupping is due to uneven moisture, like one side exposed to a cool damp floor and the other side warm and dry, then the fix is to turn it over. Let the moisture even out and the panel should go back to it's original shape. This drying or gaining moisture happens relatively fast, like over night, and can be corrected as quickly.
Then to prevent it, put the piece on stickers, or stored vertical, so conditions on both side of the board are the same. Once you have a finish on it the moisture loss and gain is much slower, and in use you shouldn't have that moistuŕe gradient. Also relates to why you finish both sides of the piece, so that moisture loss and gain is even.
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06-21-2017, 04:52 PM
(This post was last modified: 06-21-2017, 04:53 PM by Cecil.)
Are you confident of squareness? Lay two pieces, unglued, on the tablesaw or other known very flat surface, edge to edge, and check for a gap. Use feeler gauges or paper. Flip one end for end, to put the top side down but the same edges together and check again.
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Were the 5 pieces of red oak that made up the glue up cut, planed. or jointed right before the glue up. or had they been prepped before hand? When I see changes in boards that were stable at one point, and then usnstable after working with them, I'll assume they were planed, jointed, or sawn to a smaller size, and either the insides of the wood was much moister, than the outside, or it was all wet, and unequal amounts were taken off in the prepping stage. Anything sound familiar there Tom?
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I used "dry" boards from the lumberyard. The joined edges were not cut before joining. I had a lot of trouble with the doweling lineup and had to plane the raised surfaces after glue-up. I was able to re-flatten the pieces by clamping. Is there any way I can keep them from re-warping before I assemble and coat? It's a cradle, and I have to finish it with something non-toxic, also. Thanks.
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Is the climate of your shop (or even the room where the project will end up) significantly different than that of the lumberyard? If so, I don't think the lumber being dried is enough of a preventative measure against warping. The best thing is to let the lumber sit on stickers (small strips of wood that are very thin; two or three spread out under each board should be good) in your shop for at least one to two weeks in order to let them get acclimated before you do any work on them. I made two tables in 2013, and I let the wood for the tops sit for months before I did any surfacing on them. The tops still have not warped. Granted, they're quartersawn (VERY stable cut of wood) and have many coats of minwax polycrylic on them, but I let the tables sit out in a garage for many months when I wasn't using them (multiple seasons with vastly different temperatures went by), and the tops are STILL flat. I'm sure letting them acclimate for significant time had something to do with that.
Also, like at least one other person in this thread seemed to imply, I'm not sure the dowels are necessary. As long as you've got a tight joint and good, even clamping pressure, a long grain-to-long grain joint will be plenty strong with glue alone. A lot of the time the bond created will be stronger than the naturally-occurring bond between the wood fibers in each board.
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If the wood was not well acclimated to your shop you have to really be careful to avoid warping, so I don't do it; I try to let wood acclimate for at least 2 weeks before using it, or until the MC is within 2% of the EMC of my shop. If the RH in your shop isn't controlled and is moving a lot then maybe it doesn't matter as much because the wood will never be at equilibrium with your shop nor across it's thickness. In that case you really have to be careful with how you deal with the wood. The keys for me in that case are to try to joint/plane equal amounts off both sides of the boards so the MC stays balanced across the thickness. And I never lay the boards face down on the bench; they are always stood on edge or stood up leaning against the wall so that air can circulate evenly around all surfaces. Same thing after the panel is glued up; never lay it flat on a bench.
If your only "sin" was leaving it flat on your bench, and that caused it to warp, Ian is right, just stand it up and it will likely flatten out again in a day or two. Forcing it with clamps, wetting one side, putting it in the sun, are unlikely to do any permanent good. If the MC wasn't consistent across the thickness of the boards when you glue it up, ain't nothin' ever going to make it permanently flat. In that case the only solution is to rip it back apart, wait for the wood to reach equilibrium, and then start again.
John
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