Wood movement on wider boards

[Eric Viglotti]

Hello,

I am working on an engraved serving tray idea and to do this, it looks best if the wood used is one solid, wide boards rather than a glue-up of smaller boards. I've done a few of these and have used 4/4 maple one time and cherry another time. The boards I have been using have been 9 to 10" wide and about 18" long all in one piece. Since they are wider boards, they are definitely flat sawn. I end up coating them with 2 coats of urethane on the front, back and all sides. One of them has been completed for about a month and doesn't seem to have cupped or warped, but what are the chances I can still get away with this concept? The wood has all been properly dried and is from a reputable hardwood dealer. Am I still doomed to using a board this wide for this function or do you think I might be able to get away with it? Granted it doesn't need to stay absolutely perfectly flat forever, but as a serving tray, the person using it ideally shouldn't notice anything warping, rounding or cupping.

And Dave, great post on this topic, super informative which is what led me to quote it here

Thanks!

Sean,
I apologize if this is all a review for you, but your questions made me think that maybe you aren't thinking about wood movement and why bench glue-ups are always done quarter sawn.
One of the most critical requirements for a good bench is that it is flat. This is why torsion box benches (like your door) are good assembly tables. If you're working on assembly on a warped bench, you'll have problems.

Flat sawn boards edge joined don't stay flat. Therefore, benches are not usually built that way--because it turns out to be a waste of time and wood. There's a reason bench tops and counter tops all look the same, and it's not just looks.

Remember that as wood changes moisture, the rings expand and contract. If you slice a board tangent to the rings, flat-sawn, then it will expand and contract across it's width the most. Boards almost don't change length along the grain at all. And if you saw a board where it's "width" goes from the bark in towards the middle pith of the tree (quartersawn), it will expand and contract across it's width the least. The THICKNESS of a QS board is the part that is tangent to the growth rings, so the thickness will change.

Now, if you have flatsawn boards (which 14" wide pine is likely to be), and you look at the ends, you'll see that there are rings included, it's a slice of across the surface of a log. As the board changes moisture, it will "cup" and un-cup, and they way it does it is this: The "curve" of the rings will flatten out. So if you start with a flat board, with the rings facing up like "U", those rings flattening out will make the actual board center raise up and the edges turn down.

If you edge join flat sawn boards, you should alternate the rings, up..down...up...down so as the whole thing flexes, it will on AVERAGE stay a wrinkled flat.
But that's not really what you want right? Therefore, the way to keep the top surface from cupping/flexing, is to cut boards into 2" strips, turn the strips on their side... and viola, you have them in a quarter sawn configuration now! You glue a bunch together, all the end grains should look like this: ||||||||. You alternate any grain curve like this: ()()()()
NOW when the wood moves, the top and bottom surface will remain flat, and the only movement will be that the thickness of the top increases and decreases.

If you could get a giant 2" thick slab of hardwood from a tree with 27" radius, that was cut from the bark to the center of tree (quarter sawn) then it would make a perfect bench top. Since it's expensive as hell and not readily available since 1900, we instead just buy a bunch of cheaper flatsawn lumber, cut it in strips and fabricate that giant QS slab.

When you do your glue ups, its all long-grain to long-grain, and will be massively strong without any other reinforcement or splines. The only function of biscuits, splines, etc. would be to keep it all aligned as you glued up a bunch of strips. Not otherwise needed. Many folks just glue on 2 boards at a time and build up their slab over a week or so. Or you could assemble on a flat surface... oh wait ... OK, the door would work with some paper on it, then use a router sled to flatten it. Or a planer, build two and join.

Here's a great link of more reading on the subject that I've found useful:
Basic Wood Anatomy and Behavior

Hope that helps!

[Joe Jensen]

The book "Understanding Wood" is a great resource. It shows how wood moves with humidity changes and how it moves usually about 3X more when tangential to the grain (flat sawn). The warp happens on wide boards because the grain does not run perfectly perpendicular to the face or perfectly parallel to the face but rather a combination. The science also shows that unless the finish is a super thick epoxy like finish humidity still gets through causing movement. I have a kitchen table made from 5/4 red oak that is flat sawn. The pieces are about 5" wide and I alternated the growth rings so it stays flat but between summer and winter it changes width by about 3/8". It is finished with pretty thick polyurethane on all sides. I do not believe your piece will stay flat.

[Mel Fulks]

When planing take wood off the convex side , that might change as you work. Don't set it down flat ,lean it against something when you are not working on it, put some feet on finished tray
so that air is always on both sides. If time allows plane some then stand it up with air on both sides, and check for warp
before resuming planing. Put equal number of finish coats on both sides.

[Robert Engel]

If a board that wide hasn't cupped, it simply means it is completely stabilized OR nothing adverse has happened to it yet. You would definitely want people to be aware of getting the tray very wet or storing with unequal air exposure for extended lengths of time

Personally, I think you should do breadboard ends.

Finish will not prevent movement. Neither will alternating growth rings. These are two common myths.

[Joe Jensen]

Alternating growth rings does not eliminate warping due to changes in humidity. It does however make the warp of each board smaller and when the warp alternates the overall panel looks flatter. In the college text book "Cabinet Making and Millwork" their recommendation is to have boards no wider than 3-5X the thickness and to alternate growth rings. In the book "understanding wood" you learn why wood warps. Since you can't prevent humidity changes from making the wood move, you must plan for the movement. When you see wide glue ups crack it's because there was enough movement pressure in the wide board and the panel was not allowed to move. Could be because it was glued to a bread board end or the frame underneath. Could be because it was screwed to the base in a way that would not allow movement. And, I've seen examples where the panel was allowed to expand and contract, but not warp, and because the pressure was so strong to warp, the panel cracked. You see this in exterior doors if they were not careful to use quartersawn material.

If a board that wide hasn't cupped, it simply means it is completely stabilized OR nothing adverse has happened to it yet. You would definitely want people to be aware of getting the tray very wet or storing with unequal air exposure for extended lengths of time

Personally, I think you should do breadboard ends.

Finish will not prevent movement. Neither will alternating growth rings. These are two common myths.

[Eric Viglotti]

Very good info thank you. Three questions on this:

1. Would some thin wood strips screwed to the underside help at all? Or would that just make the wood crack as it tries to move but can't? Or if it would work, how thick of wood should they be made of?
2. When you mention the epoxy option, what type of epoxy are you thinking?
3. Lastly, I see plenty of live edge things out there, like live edge cutting boards like this: https://www.etsy.com/uk/listing/6429..._click=1&frs=1 (not sure why my link is from the UK ) How are they keeping the same type of thing from happening or maybe they do have the same issue but just don't worry about it as it's understood that "live edge" may cup, bend or warp over time?

Thanks!

The book "Understanding Wood" is a great resource. It shows how wood moves with humidity changes and how it moves usually about 3X more when tangential to the grain (flat sawn). The warp happens on wide boards because the grain does not run perfectly perpendicular to the face or perfectly parallel to the face but rather a combination. The science also shows that unless the finish is a super thick epoxy like finish humidity still gets through causing movement. I have a kitchen table made from 5/4 red oak that is flat sawn. The pieces are about 5" wide and I alternated the growth rings so it stays flat but between summer and winter it changes width by about 3/8". It is finished with pretty thick polyurethane on all sides. I do not believe your piece will stay flat.

[Dennis Peacock]

The LOML wanted me to make her a kitchen table. I had several pieces of 5/4" Red Oak boards in the shop and decided to make her a table from that wood. She wanted breadboard ends on her tabletop and I told her that with seasonal wood movement, she'd see the difference between the width of the tabletop and the breadboard end...due to seasonal wood movement. She didn't understand what I was trying to explain to her. In under 1 year, she got to see what I was talking about. In the winter, the top was narrower than the breadboard ends. In the summer, the top was wider than the breadboard ends. She was asking me about it once again and I told her that from my observance over the past year, that her tabletop moved a total of 3/8", from it's narrowest point during winter to it's widest point during summer. - Now.....she tells people about her moving tabletop and then explains seasonal wood movement to those that are curious enough to sit and listen to her.

Wood moves, just how much? That depends on species.

[Prashun Patel]

A month isn't enough to notice movement. You need a full year of temp and humidity changes to understand its orbit.

You can help the tray stay flat enough by either using dovetailed battens underneath or breadboarding your ends. Keeping a serving tray flat mechanically is easier than a table.

Last, the belief that 'it looks best if the wood used is one solid, wide board' is context dependent. By cutting out the center area of wide boards and then regluing the rift and quartersawn halves together, you can sometimes end up with a more uniform looking, stable, and apparently seamless tray. I have become less religious about maintaining a wide board for wide board's sake, and have appreciated the dividends this has paid in the long run. YMMV.

[Lee Schierer]

Hello,

I am working on an engraved serving tray idea and to do this, it looks best if the wood used is one solid, wide boards rather than a glue-up of smaller boards. I've done a few of these and have used 4/4 maple one time and cherry another time. The boards I have been using have been 9 to 10" wide and about 18" long all in one piece. Since they are wider boards, they are definitely flat sawn.

I think you'll be fine. The tiger maple serving tray, about 14x20, in the photo below is made up of several pieces edge glued together to make the tray bottom. They have held together for over 20 years with no problems. Just be sure to keep your wide pieces stacked,stickered and weighted while awaiting assembly and finishing.
snaktab1.jpg
The finish was applied equally on all surfaces. Design note. The original purpose was a breakfast in bed tray so the legs fold up for storage.

[Joe Jensen]

For below:
1) The wood strips would have to be very rigid and if rigid enough the wide board may crack.
2) The finish would have to be very thick and it would look like a layer of plastic. You could build up a lot of layers of polyurethane or use a pour over epoxy finish that they use for bar tops.
3) Thicker boards warp less. I recently saw a live edge table that was maybe 30" wide and 12 ft long. It was maybe 1.5" think and warped like crazy. the shop had it on a very deep discount. Doubt they can sell it.

Read that book. The science is clear, wood moves and with the knowledge of the book you can better design and select the right boards for projects.

Very good info thank you. Three questions on this:

1. Would some thin wood strips screwed to the underside help at all? Or would that just make the wood crack as it tries to move but can't? Or if it would work, how thick of wood should they be made of?
2. When you mention the epoxy option, what type of epoxy are you thinking?
3. Lastly, I see plenty of live edge things out there, like live edge cutting boards like this: https://www.etsy.com/uk/listing/6429..._click=1&frs=1 (not sure why my link is from the UK ) How are they keeping the same type of thing from happening or maybe they do have the same issue but just don't worry about it as it's understood that "live edge" may cup, bend or warp over time?

Thanks!

[Mike Henderson]

Couple of things I do to address this issue.

For a serving tray, I make the bottom fairly thin, maybe a quarter inch thick (and sometimes thinner) and the bottom is captured in a groove in the sides. If the sides are wide enough (say 2 inches, maybe less) they will keep the bottom from warping. Someone earlier mentioned breadboard ends, and the sides, in-effect, act like breadboard ends. I never had a problem with the bottoms of my trays warping.

You do need to give some space in the grooves to allow for the expansion of the bottom. You can put space balls in the groove on the sides to keep the bottom tight (so it doesn't rattle).

The second way is to use veneer. You can purchase wide veneer if you want it to look like a single board. Attach this to 1/4" MDF and you have a stable, strong bottom. You can do a different veneer on the show face and the bottom if you want, or put a design, such as a radial match, on the bottom if you want plain on the show face.

Mike