Hi David,
We used urea glue for the face veneering operations, and all pressing was
done in multi-layer hot presses, using 1/8" thick 60" x 72" aluminum cauls
(plates) on either side of the "sandwich" of five ply. The presses would
accomodate about 12 or 15 layers, and were steam heated by coils running
through each layer. Quite a plumbing nightmare, with flexible hoses and
joints to accomodate the layers opening and closing. Temperatures and
pressures were adjustable, depending on what we were laying up. The plant
was not air conditioned, and in the dog days of summer, the area around the
hot presse would reach 130 degrees. I don't know how those guys could stand
it for an 8 hour shift!
We also had "cold presses" and used a different formulation of animal glue
that was mich slower curing, overnight in almost all cases. Cold pressing
allowed us to lay up very thick stuff, like the 41 ply pin blocks we used in
the grands (the panel that holds the tuning pins).
We also used some polyvinyl and a few other types of glues for some of the
assembly operations, like applying moldings to lids, and even had a special
formulation for some of the high frequency gluing presses (radio frequency
curing, sort of like your microwave at home, but way bigger)!
One of the keys in keeping panels flat is allowing for the amount of
moisture (water) that is added to a panel each time it goes through a gluing
operation. Whether it be hot pressed, cold pressed or other, gluing dumps a
lot of moisture (and therefore instability) into elements that you have
taken a lot of care to get pretty dry before you glue it up, so that
moistture has to come out. We had "hot houses" to condition the stacks of
panels while they were coming back to equilibrium after pressing, and we
actually had tons and tons of pieces of old railroad iron (3' sections of
track) that we would pile up on the tops of the stacks to hold the top 5 or
6 panels down flat. These stacks of panels would typically stay in the hot
house for 72 hours to get the moisture from the gluing operations back out.
In fact, the 9' concert grand rims (the big serpentine curved piece that
forms the side wall of a grand piano) were about 3-1/2" thick, with 29 plies
of 1/8" hard maple veeners, and these monsters had to stay in their special
hot house for 21 days to cure out. Otherwise they would end up looking like
a pretzel!
babygrand
"David" wrote in message
...
babygrand wrote:
Hi Gary,
I designed pianos for Baldwin for 27 years, and I always found it wise
to
pay particular attention to "balanced construction". Whenever I strayed
from
this fundamental principle, it usually came back to bite me in the butt!
The term "balanced construction" applies not only to physical properties
such as veneer thicknesses and grain direction, but also to moisture
content. In addition, we always tried to use a five ply construction,
using
a core or substrate from either edge glued lumber (usually poplar) or
either
particleboard or MDF; two faces of veneer (usually .028" to .036"
thick),
and then two inner plies, between the faces and the core, of poplar
cross
banding, usually .125 thick. The cross banding, as it was called, was
laid
at 90 degrees to the grain direction of the core and two faces,
primarily to
give strength to the laid up panel, and to resist warping or twist. MDF
was
actually superior in its stability to wood cores, but of course much
heavier, and caused problemns when you had exposed edges of MDF to
finish
(or hide).
As to the moisture content, we always tried to dry our lumber cores to
between 6 and 7% moisture content, and preferred the cross banding
around
10%, and the face veneers between 8 and 10%. In many cases, we used
different specie for the "lining veneer face" (the underside or backside
of
the panel). We normally used gum veneer for this, but were very careful
that
the moisture content of the gum matched whatever specie we were using
for
the face; i.e., walnut, cherry, oak, mahogany, maple, etc. Making a
panel
with dis-similar thicknesses of face veneers, or worse, no lining
veneer, is
almost a sure recipe for disaster, even with a very thick or rigid
substrate.
Where we really got off into the wilderness was when we used highly
figured
veneers for accent pieces, or decoration, such as flame crotch mahogany,
or
different type of burl veneers. These pieces typically had a grain
direction
that wandered all over the map, and we usually use a lining veneer grain
direction of 45 degrees away from the face veneer. These were always the
hardest panels to keep flat, and we learned that there were some things
to
simply avoid, as they were were nearly impossible to keep flat and free
of
warp or twist.
However, if you pay close attention to "balanced constructiuon", it will
usually turn out well.
For further reference, consult a publication by the US Forest Products
Lab.
They have a "Wood Handbook" that is quite detailed, but contains a
wealth of
information about wood characteristics as they apply to furniture
making.
Just do a google search, or check out
http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm Most
of
the chapters can be downloaded in Adobe .pdf format, and are rich in
useful
information for any woodworker.
Hope this helps.
babygrand
"
GeeDubb" wrote in message
...
At the end of last year I made a chess table for my daughter using a
method
by David Marks. I varied some things using what I had in stock such as
using 1/2" birch ply (instead of 3/4" apple ply....) as well as cutting
the
veneer a full 1/4"+ thick vs. the 3/16" Marks used. Now in reading the
write up of the show on DIY.com I saw nothing relating to veneering both
sides of the ply but in watching the show I notice that Marks did indeed
veneer both sides though he never covered this step.
The table turned out fine as I framed the checkered glue up rather
quickly
and experienced no warping. Trying to be thrifty I also constructed two
more chess boards (hoping to sell them at a later time) setting them
aside
while I finished the table for my daughter. A couple of months have
gone
by
and to my surprise, both of these boards warped, one quite badly and the
other enough to notice.
I know there have been discussion about the need or not of balancing
veneers
but there never seemed to be a real consensus. I ended up adding 1/4"
veneer to the back side of the board. Of course this didn't bring the
boards back into flat but I was able to sand each board flat w/o them
re-warping. It's a good thing I cut these so called veneers so thick
otherwise I would have wasted some perfectly good quilted maple and
walnut.
Now the big question, when balancing veneers on a substrate should the
veneers be similar in density? I ask because I ended up using alder to
balance the maple/walnut. Another question, should both sides be
finished
equally? By this I mean oiled/varnished/lacquered with the same number
of
application coats?
Gary
I was therefore I'm not.....
Now that's a post that makes reading the NG worthwhile! 
What glue(s) did you guys use for veneering? clamping/cauls or vacuum?
Dave