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Question About Seasonal Wood Expansion

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Forum topic by Rex B posted 852 days ago 1047 views 0 times favorited 7 replies Add to Favorites Watch
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Rex B

310 posts in 875 days


852 days ago

Topic tags/keywords: lumber wood movement expansion red oak question

Hi guys. So I am starting to build a coffee table based on an “I Can Do That” article from Popular Woodworking back in 2008. I like the look of the table, and it fits my skill level pretty well. You can find the article here, but you have to be registered with the site to view it. Here is my solid model of the table:

My concern with the design is that it involves a solid wood panel surrounded by a solid frame, and it seems like the top will expand/contract across the grain and bust something apart. The author tells you to join all 8 aprons to the legs with pocket screws, which I am planning on doing, then hammer a few nails through the aprons into the tabletop. He then goes on to briefly explain that using nails here will allow for seasonal expansion because they can bend back and forth. But having the aprons (including the short ends) pocket screwed to the legs makes a rigid external frame, so does allowing the wood to move inside this frame really help? The wood is red oak.

The solution I came up with, with the help of a friend and fellow woodworker, was to use plywood for the top and shelf. I got some nice plain-sliced plywood and cut it into boards, which I will shuffle around and then glue up as if I were using solid wood. Hopefully this will disguise the fact that it’s plywood. I have already started down this path, so I’m not so much looking for solutions here, but rather opinions as to whether my concerns were well founded or not. I think the table will turn out fine the way I am building it. It just surprises me that a magazine would publish a seemingly poorly-thought-out design.

Sorry for the wordy question. Thanks in advance for your opinions/discussion.

-- Rex


7 replies so far

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CharlieM1958

15683 posts in 2843 days


#1 posted 852 days ago

I’d have to agree that the design seems a little suspect with regard to wood movement.

I’m not sure how to do it without changing the design completely, but I don’t think I’d attempt to glue up pieces of plywood as if they were boards. In my experience at least, you can never glue up a panel so perfectly that it doesn’t need planing or sanding to level the joints. Try that on plywood and you stand an excellent chance of going through the top layer of veneer, resulting in an ugly mess.

-- Charlie M. "Woodworking - patience = firewood"

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Rex B

310 posts in 875 days


#2 posted 852 days ago

Good point Charlie. The design actually uses battens underneath the panels.

Each plank is screwed to these battens from the underside, so I’m not relying on glue on the plywood edges for strength and alignment. Hopefully this will eliminate the concerns you brought up.

-- Rex

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CharlieM1958

15683 posts in 2843 days


#3 posted 852 days ago

Maybe so….. if I’m wrong, it won’t be the first time. :-)

-- Charlie M. "Woodworking - patience = firewood"

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rance

4128 posts in 1785 days


#4 posted 852 days ago

The saving grace for this looks to be the slatted shelves. It does not appear that they are edge glued(judging from the use of the cleats underneath, also the fact that they show the lines separating them). If it were solid from edge to edge(or glued edge to edge), there would be a problem. With the narrow slats, unless they are assembled tightly, then they can allow for movement . Each one is attached to the cleats underneath and they move individually, in reference to their fasteners, not as a whole shelf.

Edit: I agree with Charlie, I would not glue the plywood edge to edge. The strips are fine, just use the cleats underneath.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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Rex B

310 posts in 875 days


#5 posted 852 days ago

Thanks Rance, your analysis makes a lot of sense. You are correct, the article doesn’t call for glue between the boards, but it does say to use clamps to pull them tightly together as you screw the battens on, with one screw in the center of each board. It looks like the author was taking expansion into consideration, but it still seems like there might be problems down the road. It would be interesting to see if the one he built has developed any cracks.

So I’m still glad I’m using plywood, and will definitely use the battens to attach things. I may still use glue on the long edges of the strips, but it would just be to make myself feel better. Or I may skip that and just glue/screw the battens to the bottom.

-- Rex

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rance

4128 posts in 1785 days


#6 posted 851 days ago

It is just conjecture.

If using solid wood, the original builder will likely have problems if he pulls them together with clamps before fastening. You actually want just a little bit of slack between each one. He is correct in putting one fastener in the center of each slat.

Even with ply, I would not glue them. You might consider tongue & grove.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View a1Jim's profile

a1Jim

112008 posts in 2202 days


#7 posted 851 days ago

Hi Rex
I have helped student after student who have pulled plans and designs form magazines with bad designs and incorrect measurements and many times no thought to wood movement, You would think that someone publishing woodworking magazines would have someone who knows something about woodworking and how to check measurements. I’m glad to see you gave some thought to this design before just throwing it together.

-- http://artisticwoodstudio.com Custom furniture

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