"toller" wrote in message
...
I have a butternut shelf screwed between the legs of a table with pocket
screws. Since that is not particularly secure, I put a support under it,
also between the legs. To avoid problems with wood movement, I made the
grain run the same as the shelf; actually I just used cutoffs from
trimming
the shelf. So, while it is better, it still isn't too great.

I had a brilliant idea; replace the butternut support with a walnut
support
with grain running the other direction (across the shelf). Because of the
improved grain direction and the improved material, it will be many times
stronger.
I figure I can do this because, according to my chart, walnut moves
grainwise almost as much as butternut does cross grain. And if anyone
notices the different wood, it will simply look like a design accent.

Is this idea sound?

Certainly, if you make the holes on either end oversize to allow for
movement.

BTW, you need a new chart. Might I suggest
http://www.fpl.fs.fed.us/documnts/fp...tr113/ch03.pdf They'll let you
know that wood in general moves 0.1% overall along the grain while your
butternut moves ~ .2% per EMC percentage point tangentially (6.4/30%). EMC
summer of 15%, EMC winter of 6% means more than an an eighth per foot.