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Reply by bobro

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Posted on Cutting board and workbench grain orentation?

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bobro

320 posts in 1212 days


#1 posted 11-10-2014 07:55 PM

When you glue pieces of wood together, you theoretically get one big board. So theoretically a workbench top of flatsawn 2×4s oriented to so it’s 4 thick would move primarily in the vertical axis, as one big beam. When glued side to side, a 2 inch thick tabletop, the movement would be to the sides, as one big board.

If you cut a piece of wood and glue it back where you cut it, this does indeed act once again like a single timber, but if you glue various pieces of wood together, the movement tendencies of each might be close enough to not matter, or they very well might be contrary to each other. So you might be in essence creating a big piece of tension wood. Of course you might want to do this, deliberately, for example in the case of “smile, frown, smile..” orientation of flatsawn boards in a tabletop. The cupping tendencies (outward from the heart of the tree) will cancel each other out to a greater or lesser extent.

In the case of a bench top glued up from a bunch of flatsawn 2×4s, oriented to 4 inches thick, twist, cup and spring in the individual boards are almost certainly going to be canceled out overall. It’s possible though unlikely that you might get unlucky and glue several boards together at the edge that all have the same tendency in terms of bowing. This could make one corner of the table pop a wheelie, or take a nose dive. You’d have to be really unlucky to get enough similar spring tendency going on to bow the top as whole.

I have seen an IKEA tabletop, made of machine-scarfed boards glued up in flatsawn orientation, bow as a whole, so looking down it didn’t look like II, but ((. And somewhere I have a chunk of birch salvaged from some other IKEA thing that’s laminated up from several pieces and on paper should be extremely stable, but it has a strong twist. Lamination isn’t magic, you have to think about orientation and choose the best pieces you can.

By the way it isn’t strictly true that you get a quartersawn top by turning flatsawn boards on their sides and gluing them together. It’s more of a sort of, sometimes, depends thing. You weren’t talking about that but it’ll surely come up.

Hope this is helpful- it’s so much easier to discuss when you can draw what you mean as you go.

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.


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