Friday, May 26, 2017

warping lid...

A reader asked about a lovely box he had made of white oak sides and solid zebrawood top. About a week after cutting the lid from the body of the box, the lid warped severely. Here's the story in his own words.
When I retired, in 2015, I wanted to make wooden items. Your box books got me started. By now I have made a dozen and been guided by your hand and refer to the books all the time. If you have the time I would appreciate your advice on a problem I have never had before.

8 days after completing this box the lid started to bow. 8 days!! The first week dead straight. I have tried cauls holding it bent the other way for 5 days, still bowed almost 1/8” in the middle. I can get it straight after using a heat gun, but not while the heat gun is heating it up. It straightens as the wood cools off to room temperature, but after an hour it bows again?! 175F degree oven for a few hours which does the same thing as the heat gun, as it cools, it’s straight, but a few hours later, it’s bowed again?! Sprayed water on the concave side to increase swelling put on the cauls, let it dry overnight, no effect. I have 12 days to correct this problem before presentation to a HS grad, my granddaughter. The lid and box are white oak, and the grain pattern flows around the box, ( so I don’t really want to redo the lid) and that oak was dead flat and straight AND dry when I cut it. It had been in the shop two years. The lid insert is book matched Zebrawood panels 3/8” thick I cut from a bigger piece. I believe it was dry too. But I never put a meter on it. I believe the problem is in the Zwood. It was a very tight fit inserting the Zwood into the rabbeted top of the box, before I ran it through the tablesaw to separate the lid from the box. But why 8 days to show up!?
My questions in response where:
How is the lid panel held in place? Is it a floating tongue and groove panel or is it simply glued in place? If it is glued in place, the answer is easy. To my eye it seems immediately apparent that it’s a tight fit, and that the zebra wood panel has expanded, forcing the lid to bow.

It appears to be a lovely box, but for the problem you (he) had with it. Dealing with expansion and contraction of wood is a challenge. Both expansion and contraction offer challenges. Build without allowing for expansion and the problems do not take long to become apparent.
It turned out that my observation was right. He had glued the panel in place. A painful lesson learned. Wood as it expands and contracts can exert an amazing amount of force. It can push joints apart, or if glued in place, will likely bow. So how can he fix it in time for his granddaughter's graduation?

I have had some luck getting boxes to come apart after removing the metal parts and putting in the microwave. It sounds crazy, but I’ve put just a bit of water in the corners of the joints and heated for as long as 15 seconds at a time.

That can soften the glue (elmers or tightbond) to the point that things can be moved or even pried apart. But the top panel being glued in place will require a lot of steps in the microwave and there is the risk of irreparable damage.

It may just be better to bite the bullet and make a new lid. And the lessons learned, painful as they are, will not be forgotten. The reader suggested that I share this to help others avoid a simple mistake. Allow solid wood panels the opportunity to move. They will.

I learned my own lessons in this regard and what my reader experienced is not uncommon.

Make, and create.

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