Expansion gaps for flawed design.

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Forum topic by ShaneMartin posted 03-22-2011 10:28 PM 814 views 0 times favorited 4 replies Add to Favorites Watch
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4 posts in 2042 days

03-22-2011 10:28 PM

I have a random question for anyone out there. In a very bad lapse of design judgement, I put a picture frame border around a solid slab table top. This is obviously going to be compromised before too long due to expansion. The idea dawned on me of putting expansion gaps in the underside of the slab. The 1/4” expansion gaps would run lengthwise with the slab, spaced every 4” or so, and the depth would be 1/4” shy of the thickness of the top. The gaps would stop just prior to running into the frame border.

My thought is that it’s all about push and pull and whether the hygroscopic forces exceed the force that the glue joint/wood fibers provide. Just wondering on the chance of this working.

4 replies so far

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#1 posted 03-22-2011 10:39 PM

if your wood expands and is trapped by the frame, it will bow up in the thin spots and create raised lines, and if it shrinks, instead of a clean glue joint failing, it will tear the board right apart where it is thin, giving you a big ugly crack, you are just moving the weakest link in the chain instead of removing it, and overall, weakening the whole top. if you want to resolve this, chop off the ends and make up the length with a breadboard end with expansion space. If that doesnt fit with your style, I suggest you either live with the split miters and seems, or seal the hell out of the top with a good shellac to minimize moisture movement, and hope for the best. worst case: you make a new top.

maybe someone on here will be more creative with a solution, but as far as traditional techniques, I dont think you have many options.

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#2 posted 03-22-2011 11:35 PM


What kinds of wood did you use for this project? Unless it’s something REALLY reactive I don’t think you’ll have much to worry about. We tend to overstate expansion problems today what with the stabil environment created by central heat and cooling. If this were mid-eighteenth century New England, you could have cause for concern, but I wouldn’t worry. I have built stuff with massive cross-grain problem potential, painted one side and left the other bare, and after years of use and abuse, they still look as new. As Drew says, the worst would be you start over. Doing what you propose would crreate a self-fulfilling prophecy. Leave it be and see what happens. You might be pleasantly surprised.


-- Steve in KY. 44 years so far with my lovely bride. Think I'll keep her.

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222 posts in 2508 days

#3 posted 03-22-2011 11:46 PM

I agree with steve that unless splitting would be a disaster, if you are selling the piece or whatever else, leave it and you may get lucky, sealing it well will help. but I disagree that swelling is not an issue, it really depends on where you are. I live in Massachusettes, and I have a 14×14 end table I built 5 years ago thinking I could ignore this, checkerboard top with frame, within two years it opened every miter, and one of the seems along the end grain of the center, that side of the frame was only attatched to about 3 inches when it finally broke off. I still havent rebuilt the top, every winter it looks great, every summer those miters have a 3/64 gap that drives me nuts, oh and once they separate, there is nothing preventing bowing, so one of the corners doesnt sit flush even when it does shrink.

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4 posts in 2042 days

#4 posted 03-23-2011 12:18 AM

thanks for your replies guys. to answer yalls questions…the slab is black walnut, measuring 1” thick by 47” long by 17 1/2” wide. the border is 1/4” peruvian walnut on the inside with 1 1/2” black walnut on the outside. As far as my location goes, I currently live in NC, but will be moving to San Diego in June, which who knows what that change in humidity will do. As far as sealing it, I’ve put a couple of coats of that Maloof finish on, and will probably put on some poly to finish it off.

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