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?

You probably wonder how I ever get anything built, working like this.
Fortunately I have a lot of time.

"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.

"George" george@least 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?

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.

If I am reading it correctly, table 3-5, butternut moves 6.4% tangentially
and walnut moves 5.5% radially, for a difference of 0.9%.
That is closer than the radial differences of most woods, and everyone says
to ignore movement radially. (Of course, everyone could be wrong.)

We must be reading different charts, because table 3-5 says butternut is
very stable, while your figures show it is very unstable. What table are
your figures from?

"toller" wrote in message
...

"George" george@least 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?

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.

If I am reading it correctly, table 3-5, butternut moves 6.4% tangentially
and walnut moves 5.5% radially, for a difference of 0.9%.
That is closer than the radial differences of most woods, and everyone
says
to ignore movement radially. (Of course, everyone could be wrong.)

We must be reading different charts, because table 3-5 says butternut is
very stable, while your figures show it is very unstable. What table are
your figures from?



Once again, having difficulty interpreting your question. I see a long
piece with grain running E-W prospectively screwed to a flat piece with the
grain running N-S. I interpret cross-grain as tangential, long grain as
along the piece.

The figures from 3-5 represent the average from ~30% MC - the fiber
saturation point - where wood begins to shrink, to zero MC - oven dry.
Thus you take the percentages, divide by 30 to get the % for a 1% change,
multiply for total change.


Look at 3-1, where A is influenced mostly by radial, B by tangential
shrinkage. The virtually shrinkless dimension is along both, not across.
If you put a long-grain rail across a tangential, or even radial grain
board, you'll want to allow for the movement as indicated.

In woodworking, success allows for the movement by fixing the wood where we
want the relationship to be unchanging, and "floating" the other attachment
points.

Look at 3-1, where A is influenced mostly by radial, B by tangential
shrinkage. The virtually shrinkless dimension is along both, not across.

You are correct, I was confused. Thank you for pointing it out to me. My
chart isn't wrong; I just didn't understand it. In fact, my chart says 1/8"
over a foot, which is what you got also.

But, the text with my chart ("Wood" by Fine Woodworking) says that the
movement is reduced by half when varnished; so that is 1/16" over the 12"
shelf.

The problem is that both the cross grain butternut shelf (fortunately most
of the grain is radial) and the ripped walnut are pocket screwed to the
legs. The shelf can't expand its 1/16" without putting stress on the
support's screws.

The screws have 10 threads per inch. If I back each screw off a half turn,
that will be putting 1/10" of slack into the supports; so when the shelves
swell, they will not stress the support.

Does THIS make sense?

"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?
--

-Mike-

"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.

"toller" wrote in message ...

I had a brilliant idea; replace the butternut support with a walnut
support with grain running the other direction (across the shelf).

Is this idea sound?

If I understand your post correctly, your main concern revolves around the
'cross grain' situation betwen the shelf and its support(s)?

From your description, the way you attach the supports to the _legs_, if you
are indeed doing so, should be irrelevant for all practical purposes.

If there is no mechanical attachment between the shelf and the new supports,
IOW, no screws, nails, brads, pegs, etc.or glue, and the shelf is just
sitting on the support(s), then wood movement should not be a problem
between the two.

However, most any time you create a "cross grain" situation between two
pieces of wood that are _fastened_ together in some manner, you will need to
address the cross grain situation. There are a number of ways to do this.

But, you can't really get a definitive answer until you specify the method,
if any, by which you are attaching the new support(s) to the under side to
the shelf?

--
www.e-woodshop.net
Last update: 11/06/04

"Swingman" wrote in message
...
"toller" wrote in message ...

I had a brilliant idea; replace the butternut support with a walnut
support with grain running the other direction (across the shelf).

Is this idea sound?

If I understand your post correctly, your main concern revolves around the
'cross grain' situation betwen the shelf and its support(s)?

From your description, the way you attach the supports to the _legs_, if
you
are indeed doing so, should be irrelevant for all practical purposes.

If there is no mechanical attachment between the shelf and the new
supports,
IOW, no screws, nails, brads, pegs, etc.or glue, and the shelf is just
sitting on the support(s), then wood movement should not be a problem
between the two.

However, most any time you create a "cross grain" situation between two
pieces of wood that are _fastened_ together in some manner, you will need
to
address the cross grain situation. There are a number of ways to do this.

The shelf is pocket screwed to the legs, and the support is pocket screwed
to the legs.
The butternut support is also screwed to the shelf. I had planned on doing
the same with the replacement walnut support. As a former engineer, I know
that stacked beams are substantially more rigid when fastened together.

However, my belief is that grainwise walnut and crossgrain butternut are
close enough in movement that it is not an issue. If I am wrong, I can
sacrifice the screw between the two; the walnut support will still be much
stronger than the butternut.

Thanks.

"toller" wrote in message

However, my belief is that grainwise walnut and crossgrain butternut are
close enough in movement that it is not an issue.

Don't count on any cross grain situation not causing some trouble over time
unless you fasten the two correctly. It does not have to be involved. As has
been suggested, if you are going to use screws, just slot the screw holes in
the walnut supports in the direction of anticipated movement of the
butternut shelf and you should be fine. If you make the screwholes oversize,
consider using a washer under the head of the screw if it doesn't show.

If I am wrong, I can
sacrifice the screw between the two; the walnut support will still be much
stronger than the butternut.

You are absolutely correct, any wood span should be stronger with the grain
running lengthwise.

--
www.e-woodshop.net
Last update: 11/06/04

"toller" wrote in message
...


The shelf is pocket screwed to the legs, and the support is pocket screwed
to the legs.
The butternut support is also screwed to the shelf. I had planned on
doing
the same with the replacement walnut support. As a former engineer, I
know
that stacked beams are substantially more rigid when fastened together.

However, my belief is that grainwise walnut and crossgrain butternut are
close enough in movement that it is not an issue. If I am wrong, I can
sacrifice the screw between the two; the walnut support will still be much
stronger than the butternut.

Thanks.



Hey toller, can you post a pic of your table over on ABPW?
--

-Mike-

Hey toller, can you post a pic of your table over on ABPW?
--
My internet company doesn't do ABPW, but I already posted a picture of it on
my website to show the person I am building it for.
http://www.frontiernet.net/~toller/table.jpg

You can see the area I am concerned about in the lower left. The shelf is
butternut, the grain goes the length of the table. The shelf support is
walnut, grain goes perpendicular to the shelf.

The grain in the side panel is the same direction as the shelf and the top.

(The top is on temporarily, just to show proportions. It still has to have
a finished edge put on it.)

On Thu, 20 Jan 2005 16:36:42 GMT, "toller" wrote:


Hey toller, can you post a pic of your table over on ABPW?
--
My internet company doesn't do ABPW, but I already posted a picture of it on
my website to show the person I am building it for.
http://www.frontiernet.net/~toller/table.jpg

You can see the area I am concerned about in the lower left. The shelf is
butternut, the grain goes the length of the table. The shelf support is
walnut, grain goes perpendicular to the shelf.

The grain in the side panel is the same direction as the shelf and the top.

(The top is on temporarily, just to show proportions. It still has to have
a finished edge put on it.)



float the top, the side panels and the shelf. put solid stringers
between the drawers, at the top and bottom of the side panels to match
the ones supporting the shelf. and use a better joint than pocket
screws.

"toller" wrote in message
...

Hey toller, can you post a pic of your table over on ABPW?
--
My internet company doesn't do ABPW, but I already posted a picture of it
on
my website to show the person I am building it for.
http://www.frontiernet.net/~toller/table.jpg

You can see the area I am concerned about in the lower left. The shelf is
butternut, the grain goes the length of the table. The shelf support is
walnut, grain goes perpendicular to the shelf.

The grain in the side panel is the same direction as the shelf and the
top.

(The top is on temporarily, just to show proportions. It still has to
have
a finished edge put on it.)



Thanks for posting that link toller. It's much easier to consider these
things with the visual. I would not worry about the cross grain condition
presented by the shelf supports on the ends of the table. Remember that the
movement numbers you see in the charts are for unconstrained wood and you
have wood that is constrained by the assembly. Look at the table in your
kitchen for example - it has this very same construction. Look at styles
and rails in a typical face frame construction - same thing. Cross grain
construction does not make an absolute problem condition.

There - having said all of that... this thread has gone on long enough that
I need to ask - were you originally posing your questions because you are
concerned for cross grain construction as a principle, or because you are
dealing with a problem? If memory serves, you did not state a real problem,
but more of a concern. But then again, I've often had to admit that my
memory was the second thing to go...


--

-Mike-

"toller" wrote in message ...

Hey toller, can you post a pic of your table over on ABPW?
--
My internet company doesn't do ABPW, but I already posted a picture of it
on
my website to show the person I am building it for.
http://www.frontiernet.net/~toller/table.jpg

Sorry to say it, but your design, as shown in the photo is probably not the
best for longevity.

Then again, it may last forever.

Next time consider using M&T joints for the "rail" (your "support") between
the legs, and attaching a "cleat" to the inside of the rail as the shelf
support. Then attach the shelf to the cleat with screws in oversize or
slotted holes.

Here is poor picture, but a much better way, but not the only one, to attach
a lower shelf between table legs:

http://www.e-woodshop.net/files/ShelfSupport.JPG

Be particularly wary of the advice you've received in this thread to
"ignore" cross grain situations ... it is simply wrong and misguided.

Hell, just ask to see some samples of their work before making up your mind
to rely on such advice.

--
www.e-woodshop.net
Last update: 11/06/04