Wood expansion

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Forum topic by lateralus819 posted 06-26-2015 01:14 AM 927 views 0 times favorited 6 replies Add to Favorites Watch
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2241 posts in 1913 days

06-26-2015 01:14 AM

I need to add a bottom to a box. I was thinking of using a solid wood bottom. Poplar.

Would 1/8” allowance be enough over a 12” width? Im gonna try and get a piece thats QS or close to it.

Also would I just glue one side like on drawers?

6 replies so far

View Ghidrah's profile


667 posts in 1246 days

#1 posted 06-26-2015 01:54 AM

I think it depends on the MC of the piece when its milled, if it’s high the piece will shrink more and become very sloppy. If it’s dry, low mc when cut it should be fine.

-- I meant to do that!

View jerryminer's profile


927 posts in 1465 days

#2 posted 06-26-2015 03:41 AM

Here is a great on-line resource for figuring shrinkage rates for various species and moisture conditions:


-- Jerry, making sawdust professionally since 1976

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927 posts in 1465 days

#3 posted 06-26-2015 03:44 AM

Also would I just glue one side like on drawers? – lateralus819

What? never heard of that. I don’t glue my drawer bottoms. If you want to glue, I would just glue the center area—-maybe 2-3 inches

-- Jerry, making sawdust professionally since 1976

View jdh122's profile


1018 posts in 2841 days

#4 posted 06-26-2015 06:01 AM

According to the shrinkulator, yellow poplar could vary by as much as 0.21 inches in QS and 0.38 inches in flatsawn over a 12 inch width. Seems like a lot to me, and it’s based on the guess that the woods moisture content could vary from 4 to 14% over the seasons, which seems a bit high. If it were me I’d allow for a bit more than an eighth of an inch, but as Gidrah says, it depends on the moisture conditions of the wood at the time of construction. Buiding it in the summer means that the wood is probably relatively expanded so you want to leave less room for expansion but ensure that it won’t fall out when it shrinks.

If you can get QS eastern white pine, it’ll only move by about a tenth of an inch over those same moisture content estimates.

-- Jeremy, in the Acadian forests

View SirIrb's profile


1239 posts in 1254 days

#5 posted 06-26-2015 11:22 AM

Why not 1/4 ply fitted into a 1/4 oversized dado?

-- Don't blame me, I voted for no one.

View djwong's profile


176 posts in 3243 days

#6 posted 06-28-2015 08:31 AM

I made some 13in wide trays with 3/8in thick vertical grain douglas fir panels I glued up. I usually cut 3/16 grooves on all sides to house the panel. I allow 1/8in (more or less) clearance on all four sides. The panels I use are dry and have acclimated to my workshop for several months.

-- David W. Cupertino, CA

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