Noob Question - flattening a cupped 1/4" maple board

[Sam Shane]

Hey all,

So, I have some 1/4" maple boards I had planed down (from 3/4, all that Home Depot had) to use as a top of a Jewelry box.
Unfortunately, I discovered that even after planing, somehow I ended up with a cupped piece.
I'd say the apogee of the cupping is a good 1/8", so re-planing it with some supports would leave me with a board far too thin.
For maple, would doing a few days soaking and then a few days clamped be a safe bet? Not sure how that works with woods as dense as maple,
nor if the process is not appropriate for maple.
These were from Home-depot, so I'm not sure of their kiln-dryedness, just plain old maple planks home depot has racks of (usually 8' x 3.5' x 3/4" planks)
Worst comes to worse i'll just start over, but this was some nice birds-eye maple, wish I could make it work...

Thanks all!

[Osvaldo Cristo]

I would cut them longitudinally, square the edges and glue them matching grain.

[Mel Fulks]

You can put some water on the convex side. That's seemingly counter to logic, but it often works. It makes the wet side
more bowed,but when it dries it flattens. Water makes the cells swell. The cells become elongated and do not recover
original roundness, so that side will shrink in drying and pull flat. Probably best to keep the wet wood flat ,that will
put more pressure on the cells

[Zachary Hoyt]

If you have a clean concrete floor try laying the wood on the floor with the arch of the cup up for a day or two. The humidity in the floor will help it uncup, and sometimes will make it cup the other way if you leave it too long. Setting something heavy on the arch to help flatten it is a good idea too.
Zach

[Vince Shriver]

Zachary, your post brought to mind the same technique but long forgotten. One exception, as I recall, one side of the wood (I don't remember which) was dampened with water. I do remember this: it worked.

[johnny means]

Trying to un-cup a board is a fool's errand. All you'll be doing is introducing temporary change that will eventually revert to the boards natural state.

[Thomas McCurnin]

If the top of the box is going to be captured in a dado or mortise, and the top is fairly small, then when straightened it may not re-cup.

I would soak the board in veneer softening solution (or make your own 1 gal distilled water + 8oz of glycerin), and put the top in a veneer press (a couple sturdy pieces of plywood with cawls and lots of clamps) and leave sandwiched in between packing paper for a few days. No harm trying.

[Derek Cohen]

It depends on how long it was last planed, and how it is resting. Many freshly planed boards, especially this thin, may cup a little. This is especially so if the air around them does not circulate evenly and allow them equal drying.

I sticker and clamp all freshly planed boards, especially the thin ones. I would do this, and leave it for a week.



If there is still a slight cup, but it straightens out inside a frame, or similarly straightens out when ends are dovetailed or mitred together (with reinforcement, such as a spline), then you are generally good to go.

Regards from Perth

Derek

[Mel Fulks]

I disagree that the fix is only temporary, it's a method that has been used on some fine pieces by places that have a big budget, and the cells squeezed to a
skinny oblong shape pull the board flat. I have not seen any numbers on percentage of successes,but I'm sure there are
some failures. It's a method more appropriate for old tables that have cupped from frequently having been wiped with
a damp cloth than new wood, but it can work for that too.

[johnny means]

In all my years working wood I've seen many attempts to reverse cupping, never have I seen a board returned to flatness.

[Sam Shane]

In all my years working wood I've seen many attempts to reverse cupping, never have I seen a board returned to flatness.

Thanks all for the advice! I apologize if I don't respond to each individually, but I am reading all of your responses, thank you.

I fear Johnny might be right. Tried the humid-floor method, put it out for a day, flattened out nice, and then...with in a few hours...cupped right back.
I think I might be forced to redo it, or glue it onto a flat piece with perpendicular direction... Shame...not sure the the planer didn't get it right the first time, but I'm new at this.
As Derek points out with his picture, perhaps have to do that flattening work right away to make the difference...

Thanks all for your ideas.

[Andrew Seemann]

Thanks all for the advice! I apologize if I don't respond to each individually, but I am reading all of your responses, thank you.

I fear Johnny might be right. Tried the humid-floor method, put it out for a day, flattened out nice, and then...with in a few hours...cupped right back.
I think I might be forced to redo it, or glue it onto a flat piece with perpendicular direction... Shame...not sure the the planer didn't get it right the first time, but I'm new at this.
As Derek points out with his picture, perhaps have to do that flattening work right away to make the difference...

Thanks all for your ideas.

Wood is hygroscopic. If you change the moisture content of the wood, you will change its shape. The only way to keep that shape will be to either keep the moisture content the same indefinitely (which is impossible in the real world), or to fix it in place and have the design hold it flat, or as flat as the design can accommodate.

You can plane the board "flat" again, but if the moisture content changes again, it will cup again. Applying a finish will slow, but not stop the process. Planing the board again will result in a thinner board that will cup again when the moisture changes again. The flattening tricks given are handy to flatten a board enough to be attached to the work, but none are permanent; that is not possible. One of the traditional ways to cut stone was to drill a line of holes in the stone, drive in dry wood wedges, and then soak the wood, so the expansion split the stone. That is the kind of forces you are up against.

All wood moves and will always move. Good woodworking takes this into account, through both design and material selection. Some woods move more than others, maple, birch, and beech tend to be the most popular offenders. Walnut, cherry, red and white oak, poplar, and white pine tend to be more stable. But I have seen examples in every species I have used that were absolutely unworkable. Proper selection and drying are important by the supplier; no tension wood, correct drying schedule, and storage matter. Vertical grain helps reduce cupping (but can be plain looking and is expensive and wasteful to mill) flat grain is more prone to cupping (but usually has more interesting figure and is efficient to mill). Your climate will matter also. Where I am, we go from an interior humidity of about 10% in the sub zero F extremes of winter, to close to 90% in the dog days of summer, challenging to say the least.

Wood movement is one of those things that you learn with experience. I have more than a few pieces that prove I was a slow learner

[David Eisenhauer]

When you plane down your 3/4" material to 1/4" thickness, you need to take an equal amount off each side as best possible so that the exposed "moisture" of the freshly planed sides are equal. If you omly plane down from one side, one side is "wetter" than the other. I do what Derek does when I need thinner material and leave it in the clamped position until I am ready to capture it in either some type of frame or dados, with a finish to follow as soon as possible. It can do that regardless whether I use a power planer or hand plane.

[Ron Citerone]

Wood movement is one of those things that you learn with experience. I have more than a few pieces that prove I was a slow learner

What Andrew said!


Planing from 3/4' to 1/4" even with equal amounts off each face is asking for trouble.

Planing from 3/4" to 1/4" in one day makes matters worse...........plane both sides and let it rest for several days before final planing is better.

Planing from 3/4" to 1/4" in wood that has not acclimated in your shop for several weeks adds to the risk of a poor result.

Combining multiple risk factors listed above increases the chances that cupping will occur.

Wood humbles noobs as well as veterans........................part of the fun!

[Randy Heinemann]

Since you are using the boards in boxes . . .Are the edges of the boards going to be captured in something rigid? If so, it might not make a difference that the 1/4" boards are cupped. Since they are only 1/4" thick installing them in a "frame" or attaching them as part of the design to something rigid is likely too hold them in place flat. It kind of depends on what the boards are captured by and the relative strengths of the boards versus the surrounding material and if you can capture the boards on the side which will straighten the boards out.