"Mike Marlow" wrote in message
...

"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?

Is this because you're still having stability problems with the supports
in
there, or because you are exploring a bit and just want to play with the
artistic side of this? The potential for wood movement does not, by
itself
necessarily make for instability. In what way did you attach the supports
you mentioned, to the table legs?
--
The issue is not movement, but strength. The supports are attached to the
table legs by pocket screws.

Between the legs, both the shelf and the support are crossgrain, and
butternut is very weak cross grain. A more rigid attachment would have
helped; had I planned better, I would have glued the support to the shelf,
and then glued the assembly to the legs with biscuits. But I assembled the
legs to the upper case body first, so gluing the shelf in afterwards wasn't
going to happen.

So, I have to try to clean up afterwards and make a strong rigid assembly.
I don't have any figures, but I bet a lengthwise walnut support is 5X as
strong as a crossgrain butternut support, as well as being substantially
more rigid.

I did some tests and found that two pocket screws in butternut will hole my
full weight, as long as the structure is rigid. As soon as it moves a
little, it breaks apart.

And yes it is a bit artistic. I generally only get artistic when forced
into it by practical matters.

Thanks.