I have a question for those who have dealt with a similar problem. I glued three red oak boards together not too long ago and it warped (bowed) on me. The center board is about 7 inches wide and the two end boards are about 4inches wide. The center board is the one that warped on me. What is the best way to take the bow out of the table top? Is is a good idea to rip the bowed board down the middle and glue it back together with biscuits? Any suggestions??????????
Thanks,
Byron the novice wood worker
Replies
It's hard for me to imaging a bow in this situation. Did it bow or did it cup? A cup would be as if you lay your hand flat on the table and then cup your hand. A bow would be along the long edge, like the crook in your elbow.
If it cupped, and it's not too severe, you can try the re-hydrating technique. This is where you place the board concave-side down on a damp surface and heat gently the upper side. Often done on grass in the summertime.
I've used this technique a number of time for old tabletops that had warped. In your situation, I would protect the non-warped boards with a bit of plastic wrap underneath so that they don't change too much, and concentrate the humidity on the center board. A damp towel can substitute for the grass, and a heat-lamp (not tooooo close) can substitute for the sun. Let the board get just a fraction past being perfectly flat, overcompensating just a tad. Then take off the damp surface and let it sit for a few hours. If it re-cups a bit, do it again. I've never had this take more than 3 treatments to work. Then you need to get some finish on it right away to keep the moisture equal on both sides of the boards.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Thanks forrestgirl. It is cupped. Sorry for the misuse of terminology. It is cupped about 1/16" or slightly more. I will give this a try. I really do not have a heat lamp, will a kerosene heater work? or a halogen work light? Thanks for your help!!!!!!!
Byron
I'd not use the kerosene heater. The halogen would work, but be very, very careful not to get it too close. Set the lamp up and after about 10 minutes, past your hand over the surface of the boards. The heat should feel fairly even across the surface. If there's a strong focal point to the heat, move the lamp further away.
If you can't get that fairly-even feeling, you're probably better off just heating the room and not using a lamp. Your goal is to get the concave surface to absorb more humidity relative to the convex side, so heat isn't absolutely necessary, it just helps the process along some.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 1/27/2003 1:38:06 PM ET by forestgirl
PS, once you get this problem taken care of, you might want to figure out what led to it originally. How long did you have the stock in your shop before you milled and edge-glued it? It could be that it wasn't at a stable state when you joined everything up.
Sometimes, this warping will happen when a WWer mills a piece and then lays it on a table or floor and the top is over-exposed to the room's humidity compared to the lower surface.
Solutions to the above: wait a week or two before milling stock that just came from the lumber store. If you're ripping big boards to smaller boards, cut them over-sized, let them acclimate and then go back and cut them to final dimension. And, when a piece is assembled place it in a position to get even exposure on all sides. Put some kind of finish on pretty quickly if it's an expanse like a tabletop.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 1/27/2003 1:50:01 PM ET by forestgirl
I got the wood from my uncle's workshop. It seemed dry, but my garage workshop is usually between 50% and 65% humidty. I use a kerosene heater to warm it up when I am working, but it is at ambient temperature the rest of the time. I think the wood sat in the garage, about 2inches off the floor (wood stickers as spacers) for about two weeks. The board may have already had a cup in it that was not so prominent at the beginning. I will pay much more attention from now on. If i work in a garage shop, what is the best way to keep the temp. at a good level all the time? I am not sure that is possible, but I'll ask anyhow. Thanks for your advice. I will try the halogen light. Is it best to do it out in the garage or in the house?
I'd set it up in the house. That'll be dryer than the shop and get you faster results.
50-60% RH isn't too bad, actually. At that level of humidity, I'd not worry too much about temp/humidity control. It's the humidity more than the temp that creates wood movement. And that movement won't be significant in smaller pieces, but will be in glue-ups like you have now. I've been known to bring stock into the house for a few days, take it out and mill it and bring it right back into the house until it's joined and a coat of finish put on it. But that's because of the area I live in.
The kerosene heater will actually put moisture into the air of your shop, but the increase might not be all that significant. I was lucky enough to get a wood stove installed for Chrismas of 2001, and in the Great Northwest it's a real help in keeping the humidity below 90% in the wintertime.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
(Editing Note: FG, we must have been typing simultaneously! I'm going to let my note stand however, just because it seconds what you were saying.)
Byron, FG gives good advice... but before doing anything, you may want to try and determine the cause of the cupping. Was the tabletop stored improperly after the glue-up, or was the cupping due to existing tensions in the board that weren't allowed to work themselves out before final jointing, planing and gluing?
If the first is true -- for example, you laid the board flat on your workbench while the glue was drying, without allowing air to circulate on all sides of the piece -- then following FG's suggestions will work for you and rebalance the effects of differences in moisture on opposite sides of the piece.
On the other hand, if you did the glue up of the three boards right after milling them from rough lumber to finished size (i.e., jointing and thickness planing), without letting the boards sit at least overnight, the cupping my be due to natural tensions and moisture balancing in the board that have worked themselves out after the fact. In this case, FG's suggestion would only serve as a temporary measure -- as soon as the moisture applied to one side is rebalance, the tabletop will cup again. If this is the case, your options are to hand-joint the tabletop flat (assuming you don't have a jointer, planer or drum sander with the appropriate capacity) or to rip the tabletop, give the newly separate boards at least 24 hours to rebalance, then re-joint and glue the tabletop.
Oh, you might also be able to use breadboard ends or cleats underneath the piece, both running perpendicular to the grain of the tabletop, to force/hold the tabletop flat, but that depends on the degree of warp/cup, the design you're trying to execute, etc.
For what it's worth, it's best to let newly purchased lumber adjust to the relative humidity of your workshop for at least a week or two before using it (depending on the thickness of the wood). Then, you can do the bulk of your milling and cutting to size in one operation, stopping just short of getting to your final thickness and sizes. Then let your boards sit at least overnight, with plenty of air circulation, to work out their final twists, etc. The next day, finish thicknessing, joint the boards and glue up.
David
"The world that was not made is not won by what is done" -- Mundaka Upanishad
Edited 1/27/2003 2:00:12 PM ET by davamoore
David,
Thanks for your advice. The boards that I used were planned on two sides. The edges were still rough. It sat in my uncle's workshop for who knows how long and then I brought it to my house (garage workshop) and let it sit for about two weeks. The humidity is usually between 50% and 65% in my garage. I ripped the boards to within 2 inches of the final dimension then glued them up using biscuits. I then took the glued panel inside and let the glue dry over night before i took off the clamps. I guess it sat in the house on the carpet (oneside had air circulation the other did not) for about a week or so. Then I started sanding and noticed a slight cup in the center board. I was wondering if ripping the board down the middle of the center board and regluing would help. I think that your suggestion affirmed that question. I will give it a shot. Should the boards be left in the garage or taken inside? Should the panel once glued again, have space between it and the floor?
Thanks
Byron
Looks like David and I are on parallel train tracks here. Cool! I'd urge you to try the re-hydrating technique first. You have absolutely nothing to lose except a day's time and if it works, you get to keep that one wide board as is.
The fact that you left the top on the carpet for clamping leads me to believe that the board could have been quite stable, but just got out of whack during that clamp-up time. That means you have a good chance of the re-hydration working for you as long as you give the piece good all-around circulation afterwards.
Then, if after 2 or 3 cycles it doesn't stay flat, you still can go to the rip and re-glue technique.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Byron, just to continue our mutual admiration society, FG knows from whence she speaks. <smile, smile, pat on the back> I'll just add two responses to the last two direct questions you asked me.
First, I think it's most important that the boards you'll be using are treated all treated the same -- in other words, mill them all at the same time, bring all the boards in the house or leave all the boards in the garage, do your final milling (which doesn't always mean Final final -- it's perfectly OK to glue up a panel slightly oversize and then cut it down during fitting and assembly) prior to glue up at the same time, etc.
Are you doing the glue up in the house because of the temperature? If so, I'd store the boards in the house before you do the final milling, just to make sure that they settle down before glue up. A few minutes in the garage, on the jointer and planer, won't make any difference. As FG said, the humidity difference between the house and garage, not the temperature difference, is more of an issue as it pertains to dimensional stability.
And yes, during the glue up (while the panel is in clamps) and afterward, you'll want the boards to be up off the surface you're working on, in order to ensure even air circulation all around. You can do this any number of ways: I have little stands that my pipe clamps sit in, that hold them an inch or so off the workbench; others lay a couple of 2x4s across their workbench, parallel to each other, with little slots (for bar clamps) or grooves (for pipe clamps) cut in them, to hold the clamps. There are all sorts of methods... just find one that allows you to keep the panel flat and lets the air circulate.
OK, that was more than I meant to type. Sorry!
David"The world that was not made is not won by what is done" -- Mundaka Upanishad
I will also alternate the grain from now on, no matter what Andy Rae's book suggests. LOL.
Oh, now you've opened up a can of worms, my friend! :-) But I'll let others argue the merits of grain alternation!
Instead, one more unsolicited tip: Whether or not you choose to alternate the grain when gluing up boards for a panel, be sure that all of the grain rises in the same direction, if possible. If not, when you're trying to plane out glue lines or you're scraping the board smooth, as you get to a place where the grain switches from rising to descending, you'll get chunks of tearout. (Quickly followed by chunks of hair and scalp being torn out!) Remember the "petting the cat" example: pet in the direction the fur lies, not against it.
Sometimes the grain is squirrely and you just can't do this; other times, for aesthetic reasons, the appearance of the face of the board is critical and you need to resort to other smoothing methods, such as sanding or planing on the diagonal. Just be aware of it and save yourself a headache.
(I offer this unsolicited tip because at one point in my education I focused too much on the alternating grain issue, and kept surprising myself when I'd get tearout.)
David
"The world that was not made is not won by what is done" -- Mundaka Upanishad
So are you saying that grain alteration is not a good idea? I know that in Andy Rae's book he mentioned trying to get the most aesthetic look by not alternating the grain direction. Norm always seems to use the alternating grain technique. Now I am in a quandary. What is the best method for glue ups????????????
Sorry Byron, I was unclear. Let me first define a few terms (as I use them, not as they may or may not be used by others!):
First, imagine a long board: You have the two flat surfaces, the two ends (where the end-grain and growth rings show) and the long edges. In referring to the "alternating the grain" controversy, on which Andy Rae and Norm Abrams fall on different sides, the alternating grain idea refers to the growth rings. One school of thought says that, when edge gluing boards to make a panel, you should have all the growth rings for all the board curving in the same direction. In other words, when looking at the ends, all the growth rings should either face up, as in a "U" or all face down as in a... a... well, an upside-down "U."
If you do this, and the glued-up panel warps because of humidity changes, it will all warp in one direction, creating a large, panel-wide "U" -- which is what I think you ended up with.
The other school of thought says that you should alternate the direction of the growth rings in the boards to be glued up. The rings of one board face up, the next board's rings face down, and so on. If you do this, and the glued up panel warps due to humidity changes, the panel will look rippled.
The question is, what would you rather deal with? A U-shaped warped panel or a ripply warped panel? My preference is to work with a ripply panel and plane it smooth... others prefer the U-shaped panel. From an aesthetic point of view, I don't think this makes much difference on the top and bottom faces of the panel... but if you're looking at the end-grain edge of the panel, as in the ends of a table top, you'll either see a series of Us, as in UUUUUU (or their upside-down equivalent, such as ^^^^^^) or a set of alternating end grains, as in U^U^U^U^. You need to decide which you prefer.
Now, I also referred to the rise of the grain, and making sure the grain rises all in the same direction from one end of the panel to the other in order to prevent tearout while planing or scraping. This refers to which direction the grain rises along the length of the board, from end to end, and is independent of whether or not the growth rings at the end of the board are curving up or down. The best way to determine this is simply by looking at the long/thin edges of the board. You should see the lines of the growth rings, and how they are lower at one end of the board and rise up as they move toward the other end of the board (unless they're squirrely -- which is often the case -- and they go up for part of the length, then dip down, etc.).
The idea is to lay out all the boards so that the grain all rises in the same direction in all of the boards making up the panel; for this example, say, from the right end of the panel (as you're facing it) to the left end. This means that you'll start your handplaning or scraping action from the right end of the panel and push toward the left end, in the direction of the rise... like petting the cat hairs in the right direction. This will miminize tearout.
So, this is usually my process: First, I determine the best face of each board and lay it facing up. Then I decide whether I want my endgrain growth rings to face all in the same direction or in alternating directions and move the boards about accordingly. Then I determine the predominant direction of the rise in each board's grain (by looking at the long edges) and turn the boards end-for-end to make sure it's all rising in the same direction.
Then I start worrying about aesthetics: if the appearance of the panel sucks, I start playing around until I get the look I want. In some cases I can achieve the look I want and still have the rings face the way I want and the grain all rises the way it should. But to be honest, most times it doesn't -- and since I'm usually going for a particular look (unless, for example, the panel is going to be painted), I often have to compromise stability, ease of working, etc. in order to get the "look" I'm seeking. For example, when gluing up a table top it's very nice to have the grain and color of the wood right at the gluelines fairly closely matched from one board to the next, in order to "hide" the gluelines.
OK, that's a very, very long explanation, that could probably have been much shorter and clearer if I wasn't getting interrupted every 30 seconds by arriving family and phone calls. But there it is. I hope it helps.
David"The world that was not made is not won by what is done" -- Mundaka Upanishad
Thank you for the education. Great post! I am trying FG's thoughts right now, but if it does not work, I will try the ripping down the middle. Thanks again.
Byron
Here I go, butting in again! (But then again, what are mutual-admirers for anyway, LOL!)
"Once I glue it up or cut it to size, I bring it in the house for fear of the wood moving too much do to the humidity." Oooops, wrong move. If you're going to bring it into the house, do so for several days before you mill it, and then back into the house afterwards.
"I had danish oil and a coat of shellac on it, but it still moved ." Did it have finish on both sides of the wood? If not, there's your culprit.
I have a frame-type thing made of oak and finished with Watco and then poly. It was in the house (very, very dry due to centra heat) for quite a long time due to the holiday-interruption of my WWing. Took it out to the garage last week (75%++ RH) to fit plywood and plexi pieces into it. Left it out there for several days, laying on my workbench. Didn't budge.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
FG....I put finish on both sides of the boards. I usually finish things inside and out to make sure movement is minimized. I think the big problem here was the fact that the wood was most likely air dried and not kiln dried. Then that was compounded by your last comment. The fact that I left it in the garage and then cut it and brought it inside. So one last question....If the RH stays around 55% is it ok to leave the boards out in the garage until the project is finished and then bring it inside. I mean after the stain and top coats are applied? Or just go with your bring the wood inside for a day or two then take it to the garage and work with it and bring it right back in? I appreciate your patients and comments.
Byron
I really think that it would be OK to do all the work in the shop. I base this on the fact that the RH in our house in the summertime is around 55%. The only area I'd have questions about would be the actual application of finish. Since I work almost exclusively with oil/varnish mixtures, I don't know what humidity levels cause problems with other finishes.
As far as Kiln Dried vs. Air Dried is concerned, I've had far more problems with KD wood, and I actively seek out air dried. I suspect the problems with that chest can be traced directly to the humidity changes the wood was subjected to right after milling.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
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