Shelf Grain Direction & Wood Movement Help

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Forum topic by lblankenship posted 05-13-2020 11:08 PM 194 views 0 times favorited 4 replies Add to Favorites Watch
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53 posts in 1085 days

05-13-2020 11:08 PM

Topic tags/keywords: question wood movement grain direction design

Hey guys,

Quick question, I was curious which direction I should orient the grain of a shelf if it will be seated in a dado on each side? I made a small step stool for practice a couple months back and was worried if I glued the end grain in place on the dados the board would expand/contract and cause the whole thing to twist. So for the stool I glued the edge grain in place.

I’m getting ready to start a bookshelf very similar in design to the stool but I was planning on doweling the shelves in place.

I’ve attached a photo of the stool for reference and a model of the bookshelf I’m getting ready to start.

4 replies so far

View jdh122's profile


1167 posts in 3629 days

#1 posted 05-14-2020 12:18 PM

For a bookcase I would put the shelves in with the grain running from side to side. This does put the shelves in a crossgrain situation relative to the stretchers on the sides, but the shelves would be weaker in the other orientation (and funny-looking too, I think). If the shelves were in dados I would only glue the front six inches or so, allowing the shelves to expand and contract toward the back. If you’re doing dados plus dowels then put one dowel glose to the front edge and another 4-5 inches further. For a third dowel toward the back you could probably get away with reaming out the hole front to back a bit. If you’re planning dowels with no dado that’s a bit trickier, you might be able to make the back dowel hole in the shelf into a very short ellipse that will allow for movement.
Of course it all depends on scale – for the top shelf you can get away with not accounting for movement at all. The middle one might work too, but I’d be reluctant to make the bottom shelf without some kind of strategy.

-- Jeremy, in the Acadian forests

View bilyo's profile


1137 posts in 1914 days

#2 posted 05-14-2020 02:54 PM

I like your stool. Very cleaver design and your construction looks superb. You did the shelf or step the correct way. Any movement in the wood will have no effect as the legs are not connected horizontally. If you had oriented the step the other way, any movement would stress the top joints of the legs. However, in this case, because the whole thing is small, the effects would be minimal.

I must respectfully disagree with Jeremy regarding the book shelves. The same concept applies. Orienting the grain side to side will create a cross-grain situation that will likely result in splits and cracks and, possibly failed joints. If you glue or dowel only the first few inches, then you have very little holding it all together. This strategy would work with a sliding dovetail but, not a dado. If you feel that you must orient the grain side to side, then you should connect the two leg sets with stretchers or frames and then simply lay the shelves on them and fasten down with clips or similar devices. Having the stretchers will also give you the benefit of more rigidity and resistance to racking of the whole structure.

View bondogaposis's profile


5808 posts in 3162 days

#3 posted 05-14-2020 03:05 PM

You are going to have to allow for movement of the shelves in one way or another unless you use plywood for the shelves. The stool looks great, you can’t really run the books shelves in the same grain direction though.

-- Bondo Gaposis

View lblankenship's profile


53 posts in 1085 days

#4 posted 05-14-2020 04:32 PM

Thanks guys, yeah I ended up having the end grain face outward on the stool last minute because I was worried any way I attached the end grain to the legs would result in one leg getting pulled one way more than the others with expansion/contraction. Ultimately causing the whole thing to become twisted and unstable. By gluing the edge grain I would know that if it does move, the whole stool would just get slightly wider or more narrow.

I should also mention these shelves are only going to be 12” wide at their longest dimension. Not sure if that changes the concern for strength if the end grain is facing out. I might consider adding stretchers beneath and attach the shelves with clips to those and see how the design ends up. If not, I might just stick with keeping the end grain facing the front and back.

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