Movement in walnut or plywood? - Woodworking Talk - Woodworkers Forum

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post #1 of 11 Old 12-04-2016, 10:34 PM Thread Starter
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Movement in walnut or plywood?

I recently made a large top for a receptionist desk in kiln dried walnut. I used 3/4" stock in varied widths with glue and wood biscuits on the lengths and ends of the wood. Since it was a large 'L' shaped top and I wanted the look of a thicker slab, I cut a piece of 3/4" plywood to the same shape and screwed it to the bottom of the joined walnut. After about two months, the entire top is 'cupped' and far out of square. Is this due to the Walnut not being acclimated?
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post #2 of 11 Old 12-04-2016, 10:53 PM
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Yea, you got wood movement. It's not a good ideal to laminate solid wood to plywood. If the solid wood shrinks in width or expands it will either bow or split because the plywood doesn't move very much. There might not be a solution other than replacing the tops. You might remove the screws and hope the glue lets go. If that helps you could elongate the screw holes and put the screws back in. It would be better to use pan head screws and not torque them down tight. The solid wood needs to breathe.
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post #3 of 11 Old 12-05-2016, 10:33 AM Thread Starter
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That's what I thought, thanks for the reply. I wonder if only a few screws would work too so it's not anchored in as tight?
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post #4 of 11 Old 12-05-2016, 08:05 PM
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This probably isn't a acclimation problem.....it's a build issue. As Steve said solid and ply don't cooperate together UNLESS you know how to attatch each other and allow for MC changes (this will happen everyday 24/7/365 of some sort of movement). Another tip for thick look is to just add a edge around/double thickness...be sure the endgrains match also (hint make top 4" longer and wider, slice 2" off EACH end and 2" off EACH side, rotate them under keeping cut edges together [corners get mitered] you just doubled your thickness visually and the grains match perfectly and it "looks" as a slab thickness)

This is also your second post concerning build issues pertaining to MC/acclimation and wood. Nathan I think you need to study a little more in depth on moisture and joinery. Look into older craftsman methods. They had to build for movement due to very little controlled enviroments in those days. You may also have a MC control issue in your shop area from bringing in the barnwood and stacking near the KD'd wood....THEY WILL swap/try to balance MC levels making the KD go above needed specs. Try running a large basement size DH in your shop to pull RH under control. I have one running 24/7 at 45%RH = approx 8- 9%MC depending on temp. That keeps wood well balanced BUT I STILL have to build/joinery wisely...a client may not have the same convenience/control !!! You seem to have the ambition to build let's carry it to the next level and go for craftsman (a higher knowledge level).

We enjoy helping here. The advice given to you has been a long journey for me....lack of true craftsmen in my life and books (internet now). I had a lot of advice that wasn't proper and a lot of trial and error to realize everyone DIDN'T know what they were talking about!!!

We enjoy pics!!!!
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post #5 of 11 Old 12-06-2016, 12:03 AM
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Quote:
Originally Posted by nathanvaughan View Post
That's what I thought, thanks for the reply. I wonder if only a few screws would work too so it's not anchored in as tight?
You could attach plywood to solid wood if the solid wood was finished underneath the plywood. Then to prepare the plywood you would make holes that were elongated and when fastened use pan head screws and just make them barely snug. The idea is if the solid wood wanted to expand or contract it wasn't restricted in any way with the plywood.

About the finish, solid wood is much more stable if it's sealed on all sides. It's like wetting one side of a kitchen sponge, it would curl up. Wood does much the same thing so when you use any large solid wood panel such as a table top it's important to seal the underside. Wood draws moisture out of the air so if the moisture content is higher on one side than the other the board will bow. Sometimes these guys get into trouble by gluing up a table top one weekend and leave it laying on their work bench until the next weekend and what happens is the moisture in the air can get to the top but not the bottom and it bows.
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post #6 of 11 Old 12-06-2016, 10:28 AM Thread Starter
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Here is a photo of the desk I made.
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post #7 of 11 Old 12-06-2016, 11:02 AM
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That's a lot of cross grain. I think eventually you will have an issue with the boards cracking.
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post #8 of 11 Old 12-06-2016, 03:02 PM Thread Starter
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What would you recommend to make this top without movement? If the walnut was a true 1" thick with no base do you think it would move? I used a tung oil sealer
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post #9 of 11 Old 12-06-2016, 07:25 PM
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What would you recommend to make this top without movement? If the walnut was a true 1" thick with no base do you think it would move? I used a tung oil sealer
In around a decade or so the right side of the top is likely to shrink 1/8" to 1/4" in width. There is no way to avoid it with solid wood. A top of that design would have been better made out of walnut plywood and banded with a solid wood edge. Plywood would be free of any noticeable wood movement. Tung oil is a good sealer but it won't have very much to do with wood movement. Wood is a living thing and over time it will shrink and is also in humid weather swell up.

What is shown in the picture is a table top which has a breadboard end on it. When it was made the edge shown was flush and sanded smooth and over time the center part of the table shrunk leaving the breadboard end sticking out. The breadboard end doesn't shrink lengthwise.
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post #10 of 11 Old 12-06-2016, 11:21 PM
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Quote:
Originally Posted by nathanvaughan View Post
What would you recommend to make this top without movement? If the walnut was a true 1" thick with no base do you think it would move? I used a tung oil sealer
That is a beautiful top!!!

Think of solid wood as a live thing/ almost human....it breathes, it moves, it starves, it swells, temp effects it and also moisture. When it gets more food (moisture) than needed it gets fat/swells width wise but not height, when it doesn't get enough it skinnys up/shrinks width wise but not height. Too much moisture on one side the skin swells and bows one sided.

I believe the cross grain width I see would move (guessing) 1/2" or more form summer MC to winter MC (usually around 3-4% change) as a full glued top. There is a guide on this movement on the either here or www.Woodweb.com .

Movement with or without plywood backing doesn't effect the solid wood....it still moves....it's alive!!!! Always seal both sides at least 1 coat.
There are many different fastening techniques that allow solid wood to float.....slotted holes is the most common solution used for hidden fastening. Some use cleats that slide in slots.

Have a Blessed and Prosperous day in Jesus's Awesome Love, Tim
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post #11 of 11 Old 12-07-2016, 11:38 PM Thread Starter
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Thanks for all the help! I'll be experimenting with the slotted holes for the future. I did not seal the bottom of the boards so that is good to know. I'm also looking into other sealers for Walnut I just like the look of the oil.

Thanks,

Nathan
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