Wood movement

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Forum topic by Grantman posted 07-25-2010 02:39 PM 1063 views 0 times favorited 5 replies Add to Favorites Watch
View Grantman's profile


109 posts in 3445 days

07-25-2010 02:39 PM

I am building a sofa table, 6’ long x 12” wide. The base is 1/2” copper pipe and the top is 6/4 Canary Wood. Rather than one solid piece six feet long, I have two 3’ pieces “connected” by copper pipe. As you may be able to see on the attached drawing, when placing the two pieces on the top of the frame now, they’re too heavy for the top rail and it sags in the middle. I’ve exaggerated the drawing for effect. (bottom drawing)

Sofa Table

If that doesn’t work, try this.

I am planning on inserting three pieces of copper tubing to match the three bottom rails between the two slabs of canary wood. The pipe has a nominal 5/8” O.D. but actually measures .635. On a test piece last evening, I was able to bang the pipe in but it’s too tight. I think I need a 21/32” or 41/64” bit.

My question is, how much space around the pipe should I allow for wood movement? The one advantage of using the 5/8” bit is that there’s no chance of the pipes bending and therefore no dip in the middle. If I get a larger opening, the wood may sag a bit.


Thank you.

5 replies so far

View Sawkerf's profile


1730 posts in 2488 days

#1 posted 07-25-2010 03:16 PM

If I understand your problem, you’re trying to support a 12” x 72” x 1.5” thick board on a framework of 1/2” copper pipe. The board is in two pieces which will be joined end-to-end with pieces of copper pipe – sort of like dowels in the ends of the boards.

If I have this right, you probably need to add some kind of center support to your framework to prevent the joined boards from trying to fold like a hinge under their own weight. Even a single, solid, piece of lumber that size will sag a little if it’s only supported at the ends, and two pieces that are mechanically joined end-to-end will want to sag even more.

You need some kind of support under the joint.

-- Adversity doesn't build reveals it.

View Howie's profile


2656 posts in 2342 days

#2 posted 07-25-2010 03:17 PM

If I understand you correctly you are inserting the copper into the ends of the 3’ pieces to join the wood. If that’s the case the wood will expand across the table not the lenght of the table. I’d use the 5/8.

-- Life is good.

View CharlieM1958's profile


16229 posts in 3638 days

#3 posted 07-25-2010 03:44 PM

If I understand your question, which was how much space to leave around the pipe, the answer is none. You want a nice tight fit, the same as if you were joining them with dowels. Wood movement surrounding the pipe is not going to be an issue.

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

View Grantman's profile


109 posts in 3445 days

#4 posted 07-25-2010 03:47 PM

I guess the picture links didn’t work. ;-(

Sawkerf – each half of the table will be supported by four upright pieces of copper 9” from each end or 18” between the supports. The maximum span unsupported is 21” in the center between both slabs. (9” from each end and 3” between the slabs.) They’re not just attached at the ends but as evenly as I could make it.

View Grantman's profile


109 posts in 3445 days

#5 posted 07-25-2010 04:19 PM

Thanks Charlie and Howie, too, in addition to Sawkerf. I never thought of the dowel analogy but it makes sense. 5/8” it is.

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