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Gluing solid wood bottoms

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Forum topic by grego posted 11-27-2012 08:39 PM 1486 views 0 times favorited 6 replies Add to Favorites Watch
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grego

70 posts in 1248 days


11-27-2012 08:39 PM

A very basic question about wood movement.

Paul Sellers has this wonderful series of Youtube videos on making a dovetailed box. One thing he does is glue a solid wood bottom directly to the bottom of the box. I’ve read in several places how box bottoms need to “float” in grooves because of expansion as the wood absorbs moisture. Is this advice all wrong or perhaps exaggerated?

Here’s the youtube video where (at the start) he talks about gluing the bottom.

http://www.youtube.com/watch?v=gcQATQLzDuw&feature=relmfu

I tried emailing a question to the master himself about this. He seems to be an incredibly busy guy so I’m not surprised I didn’t hear back.

Appreciate the Lumberjocks’ good advice!


6 replies so far

View DS's profile

DS

2131 posts in 1087 days


#1 posted 11-27-2012 09:13 PM

Generally speaking, you are correct—you should NOT glue a solid bottom into a dovetailed box.

You CAN, however, tack glue along end grain in the center of the panel with the rest left loose—that would still allow expansion without catastrophic results.

Some people glue along only one edge for a similar result, but to me that puts a high burden on the other edge for all of the expansion clearances.

Also note that the rules can be fudged if your bottom is plywood or MDF instead of solid wood, as there is minimal expansion with these materials.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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CharlieM1958

15702 posts in 2885 days


#2 posted 11-27-2012 09:44 PM

I know it goes against conventional wisdom, but I have made many, many boxes with glued-on solid wood bottoms and/or tops, and I have yet to have a single problem caused by wood movement. I will add the caveat that here in southern Louisiana humidity levels remain pretty high throughout the year, so wood movement might be somewhat less of a problem than it is in colder climates.

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

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grego

70 posts in 1248 days


#3 posted 12-03-2012 05:55 AM

Thanks guys.

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Blackie_

3445 posts in 1179 days


#4 posted 07-26-2013 11:53 PM

Looking at the box, I think it all derives around the size of the box, such short sections of wood, there shouldn’t be much if any at all wood movement and as Charlie, mentioned I’ve made a many of bandsaw boxes and all of the bottoms are glued in place on these.

-- Randy - If I'm not on LJ's then I'm making Saw Dust. Please feel free to visit my store location at http://www.facebook.com/randy.blackstock.custom.wood.designs

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JAAune

829 posts in 983 days


#5 posted 07-28-2013 01:20 AM

I don’t remember what the rule is for cross-grain joints but door makers and old-school cabinet makers usually do have numbers they use. 6”-8” is typically the absolute maximum I’ll glue in place for cross grain joints. That’s still pushing things a little since some woods will expand and contract over a 1/16” across that distance.

I do have an old box I made before I learned real woodworking and the 10” wide top and bottom are still intact despite being glued in.

-- See my work at http://remmertstudios.com and http://altaredesign.com

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Bernie

414 posts in 1503 days


#6 posted 07-28-2013 04:35 AM

The opening comment in the video is what jumped out at me… he glued the long grain wood to long grain wood and the end pieces are short (in width) enough so the wood movement is minimized. You have to understand that wood only moves across the grain and doesn’t move the length of the wood so if your building a box 30 inches tall, 30 inches wide and 10 inches deep, the box will only move across the width of one of the 30 inch dimensions and the 10 inch depth (30 inches long) is minimal in its’ movement.

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

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