Hi, I have 10 pieces of white oak 8″ x 10″ x 1/2″ that is cupped. It started out 8/4, band sawed down to 1″, jointed one edge, jointed one face flat, using chalk. Took to planer, chalked and planed flat to 1/2. All looked good when I was done. I left it in the garage overnight and 6-8 pieces are now cupped. Can anything be done to clamp and make flat again or is it what I suspect, kindling? Thanks.
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A lot depends on how cupped and how you are going to use it. I managed to put together a blanket chest that the panels were cupped maybe 1/8" across 20" or so. It has held together 10 plus years now. The panels are dovetailed and hold each other straight.
If the panels are cupped because one side dried more overnight you can try wetting the concave side to see if that flattens it out. I have had mixed results with this.
Another option is to rip down the middle flip one side and glue. This averages the cup out but still not truly flat. But maybe close enough depending on application.
More details may prompt more suggestions. How much are the panels cupped? What is the intended use? What joinery will you be using?
Good Luck and Merry Christmas
Pics are welcome here.
The above suggestions are good. Chalk this up to learning why you want to take things down to the final size in stages. This lets you correct the movement that occurs as internal stresses are released.
Your sequence was good, a couple of days between each step would improve your odds. There is always a diff in moisture between the outside and the center of a board.
Waiting to see is the key, especially after a resaw and even more so if your wide stock is flatsawn.
If you used the surface planer to take the bandsawn board from 1" to 1/2" you, hopefully, would have flipped the board after each pass so an equal amount of wood was removed from each side of the board. That helps in stabilizing the board.
Well, as usual I learned a few things. The wood is cupped 1/8 to 3/16 across 10". I think I will start over, taking my time if the lumber is thick. Waiting to let it adjust and flipping it in the planer. I am dovetailing these and don't need any more difficulty than I will already encounter. Thanks, Merry Christmas!
I love the advice I get here, it is the first place I go. Employees at woodworking stores may or may not have experience!
Good thoughts above - will add a few...
First, extremely hard to keep fairly thin boards that wide dead flat. All suggestions above are valid. Make sure you sticker the boards while they acclimate.
Second - starting with 8/4 and resawing down the center was part of your problem. The wood was presumably was kiln dried so case hardened on the surfaces but not in the center. When you resawed the resulting boards had one side hardened and the other not. Guaranteed cupping there.
Third - For 1/2" final thickness, start with 4/4 material which is presumably 13/16"-7/8" if surfaced both sides. Then joint for flatness and run through the planer making equal passes each side. Far easier to get stable 1/2" stock that way.
Four - This sounds counter intuitive, but if you have the time/efficiency/expertise, consider milling the boards, cutting dovetails, and gluing them up on the same day - ie don't give them the time to move. Once together there should be no worries about cupping. Practice the dovetails on your 1/2" "kindling" - if machine cut, get set up and practice cuts done before hand. If hand cut, get your layout done and, again, practice.
Thanks, great additional information. What is sticking? Does applying any weight for a couple of days help keep it flat while it adjusts? I think I will stick with 4/4, that makes sense. I am making the tote on the cover of the most recent FWW, I had a bunch of 8/4 white oak and thought I would put it to use. I felt handy for a moment, then it cupped. Thanks again and Happy New Year!
To the first question about stickering, that refers to putting sticks between the wood pieces after milling to allow air flow and even drying.
As mentio0ned below, "stickering" refers to using small sticks between boards to get air flow between boards so both sides of boards are exposed to the same air flow.
Not sure about applying weights - haven't done that myself. When I cannot use the boards immediately/same day, I usually go the opposite direction which is leave boards alone just thicker than needed (typically 1/8" over) to move however they will on their own before doing final milling to desired dimension.
ral3wood, lust wanted to say I appreciate the fine advice!
As stated or alluded to in the above comments sometimes doing, or at least trying to do everything right to produce a flat panel still doesn't work.
I have a 12" diameter clock hanging on a baluster in my living room. The clock has an open back. I finally decided to cover the back by making a 1/4" thick resawn and book matched Curly Maple panel behind it. Of course, no matter what I did I couldn't keep the panel from warping. I finally decided to build 3 Cherry "ribs" that would hold the panel flat on the back side of the panel.
It worked fine and actually enhanced the look of the whole set up.
If you aren't going to use the boards immediately... I have been able to wrap boards together with the stretch plastic wrap and clamp them together to a flat surface and prevent cupping. This generally works only with wood that has already been dried to the desired moisture content (kiln dried lumber usually meets this criteria if purcahased from a reliable source). I have wrapped the entire length of the boards in stretch wrap or have also done this by merely wrapping the boards together at various points along the length and then clamping them to the flat surface.
One of the "almost certainties" with wood is that, if resawed and/or planed, the wood will continue to cup or twist if not held flat in place. It's best to wait till you are ready to use the lumber before planing beyond a rough cut thickness to prevent the problem you experienced. Even then, it's always possible the wood will move enough to cause problems. I prep quite a bit of extra to avoid having enought waste to have to search for additional wood at that point.
I learned this recently lol...thought I did everything right. I left the finished panel for a month and returned to it. Thing was a pringle.
I should not have made the thing panels until its home was ready for it, as you mentioned.
That is good advice I wish I had read it 2 months ago, lol.
Years ago Christian Becksvoort had a very funny piece in the magazine about fixing warped panels by putting them outside on the grass, concave side down. The sun on the convex side and the ground moisture on the concave side can help flatten the board. Might be a little tricky in the winter, but potentially worth a shot. https://www.finewoodworking.com/2009/05/01/working-with-warped-panels
So I really love white oak and working with it is just a ton of fun, IMO. However I was experiencing a lot of the issues you experienced. In addition to doing a bunch of the stuff referenced above, I stopped using flatsawn oak, and have gone over to quartersawn or riff sawn and I make darn sure the piece I'm using is dry. I use my mini-kiln (light-bulb powered) that I have for drying Windsor chair parts.
This has helped a lot. Plus I am now in love with the radial face of oak (and can't stand the tangent face)...
j, does your mini-kiln involve a fan? I have a 2' x 4' shelf unit that I could enclose, add a light of unknown wattage and a small fan. What does yours look like? I have a bunch of 4/4 x 4' walnut that I need to resaw.
Kurt,
I'm a Windsor chairmaker working with a lot of green wood that I need dried relatively fast, so a mini-kiln is a must have tool. There is no magic to making them in terms of what they look like beyond having a temp control unit. I use and recommend this unit: Inkbird ITC-308 Digital Temperature Controller 2-Stage Outlet Thermostat Heating and Cooling Mode (Amazon has it for $35). Very easy to use and it has been reliable.
My kiln is insulated on the inside with foam insulation from any home center. This includes the door. Door has a spring latch to keep the door tightly closed. Mine has holes on the top for chair leg mortise drying, which I can close off with insulation when not in use, but they are useful air/water escape vents.
In terms of lighting, I use a heat light bulb on the bottom, mounted on a metal stretcher.
I typically dry at 115* although I have heard of people drying at over 140*. I like 115* cause the fire risk is lower and I think a slower pace of drying is a tad better (less checks). I don't over stuff the unit. Also I don't put woods thicker than ~3/4" in there. Mine unit is something like 2x3x5' and has a removable rack.
Is a mini-kiln required for a cabinetmaker? No way. But given I have one for the chairmaking, I happily use it broadly.
J, thanks for the detail, I can build that. Do you have a little fan exhausting the moist air? I'll resaw my 8/4 in half and dry it. I sold a bunch of it to a friend, he re-sawed, planed it, stacked it up in his shop and it proceeded to cup. I am a hobbyist with a lot of wood on my hands and have some sawmills in the MO for more. Appreciate the help and Happy New year!
No Fan?
Kurt,
I don't have a fan in mine. None of my chairmaker friends have fans either. I can tell you, on spindles and legs, the unit works great and it rapidly dries a green piece to dry as a bone in a few days.
It also works good on getting that last bit of moisture out of a 3/4" board that has previously been kiln dried but has been sitting around in a shop environment.
best of luck w/ your walnut!
The best way that I found, for me at least, is to put your resawn or any jointed/ planed boards in a plastic bag and twist tied shut. The amount of wood movement is minimal. Works well if you can’t assemble or use your parts right away. For parts that are thin-3/8-1/4”- box parts for example, I put weight on top of the plastic bag to keep them from cupping.
The plastic bags are real cheap and easy to use.
I also heard Mike Pekovich say, somewhere, that when he resaws he planes or joints a thin layer off the board before he resaws to minimize the moisture difference between the resawn pieces.
Hope this helps.
rdubya, it takes a lifetime to accumulate all these little tricks. This forum is a great place to speed up that process. Thanks.