(Also Posted in abpw)
I would like to run this past the group. For years we have been told that
the best way to glue up slabs, like table tops, was to alternate the
direction of growth rings using 4"-5" boards. Occasionally this caused us
to rip and join a perfectly good 18" to 24" slab of hardwood and end up with
a slab with discontinuous grain pattern -- necessary for the integrity of
A couple of years ago I was building a 8/4 Oak table top for a coffee table
and was unsure of the best rip widths for the glue-up assembly with this
heavy material. I posted to forums of a couple of woodworking magazines and
was surprised at a response. A magazine editor said that with heavy stock,
with fairly large radius growth rings, it was ok to rip at 4" to 5" and glue
them back together in their original position. He claimed the glue joints
did an adequate job of relieving the stress and I could retain the original
appearance of the slab.
The post came slowly -- after I had ripped and glued in the conventional
(alternating) manner. The top looked fine but I still
Disclaimer: I really (really) am no expert, I'm just giving my
Say you rip the slab with a glue-line rip blade and the pieces don't
need rejointing when you are done - there has been zero movement. It
seems to me that with regard to internal stresses existing in the
wood, you've either done nothing to relieve them or they didn't exist
in the first place. Then you reglue the pieces back together, and
you've lost a few kerf-widths of wood. I'm not sure you've
accomplished anything. Does the fact that wood glue is stronger than
the wood itself make the slab stronger as a whole? Maybe very, very
slightly. If the pieces needed significant rejointing, my guess is
that you have probably increased the structural integrity of the
However, it's my understanding that the reason you alternate flipping
the boards over is to create an alternating warp pattern. Rather than
risking the whole board being in one big cup, you end up with a series
of little up and down cups across the width of the panel that tend to
even each other out.
Jay - You have hit on the concern I had. I didn't think the glue joint
would be much of a factor in controlling cupping. A saw kerf and shallow
planing might 'disappear' but the cupping still do seem to be a factor
There are certain factors to take into account :
Will the slab be held in place (such as a tabletop or a countertop)
which would help keep it from "cupping" , as opposed to.... say a lid
for a blanket chest or such. Is the wood quartersawn, in which case
the tendency to move or cup is greatly reduced. In our shop we
generally go for "the best face", matching color and grain . If it IS
for a tabletop, be sure to allow for movement by enlarging the holes
for the screws that hold it down. (or by other methods)
As I noted in response to Jay above, I am having trouble with cupping not
being a factor even when restrained as a table top. My thinking (right or
wrong) is that an 8/4 slab of oak might be able to generate enough cupping
force to damage itself as well as table structure.
Again - any one else have experience with this.
absolutely. you have to use some common sense. the skirts of the table
can help to hold the top flat, but it would be ridiculous to expect
for instance a 3/4" x 3" stick to restrain an 8/4 top that really
wanted to twist around.
you can estimate the capacities of the parts and what they will do in
opposition to each other. set some blocks a distance apart and span
them with the part in question. apply force in the center and note the
the thing that makes a table stay together is getting all of the wood
to a decent moisture content and milled for stress relief before
assembly, not forcing it to dry straight after assembly.
First, realize that it's not specifically the orientation or the absolute
radius of the rings that count in cupping, but the difference between the
smallest and the largest arc in the same piece. The science of shrinkage
says the earlywood shrinks more than latewood. Where there is
proportionally more latewood - near the heart, it shrinks hardly at all.
Look at a log left to dry on its own, and you'll see that it cracks radially
to relieve this induced stress. Split the log green, and notice that it
dries with no radial checks, but with a crowned center. Note also that the
crown you see most often - on softwood, is the result of a large change in
moisture content, beginning at the fiber saturation point, a condition the
boards should never experience again.
The answer, to me, is to get rid of that center, something rarely a problem
when hardwood lumber is sawn for grade. Only when it is sawn
through-and-through as softwood commonly is, does it become a real problem.
That's where and why I'd rip - the center of the tight arc to relieve
stress, and then I'd probably find the best match not by reassembly of cut
faces, but by mating sapwood sides.
As usual, Hoadley has a good section on this, as does the late Tage Frid.
Sun, Aug 1, 2004, 1:07pm (EDT-1) firstname.lastname@example.org (RonB) says:
(Also Posted in abpw)
I would like to run this past the group. For years we have been told
that the best way to glue up slabs, like table tops, <snip>
Dunno. I suppose in part it'd depend somewhat on what your
definition of "slab" is. I've seen coffee tables with a top cut
dianogally from logs, they're one piece tops, and seem to be doing fine.
Not sure how thiick they were. Some of them were some pretty damn bit
tables too. Some had the bark left on (not my choice), and some off.
The highway of fear is the road to defeat.
- Bazooka Joe
JERUSALEM RIDGE http://www.banjer.com/midi/jerridge.mid
I attended a 3-day seminar by Frank Klausz and he had a
definite opinion on this. He said he uses the best face
of each board on the top, regardless of growth direction.
Use dry wood and seal all sides and you won't have a problem.
For those who alternate growth ring direction and do a poor
finishing job, he said they'd get wavy slabs instead of cupped
ones. Then he laughed with us. (I trust his word since I haven't
built any large/thick/wide-slabbed furniture yet.)
Best bet: Use quartersawn wood for flatter slabs. ;)
Would you like to buy some -more- swamp land, sir?
- Let Exxon send their own troops -
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