A veneering balance


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.....
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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/fplgtr/fplgtr113/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
"

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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

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Not sure why a thin veneer "unbalanced" would be any different than five plies versus four plies. Thick veneer, I'd balance. A quarter inch isn't veneer, it's wood. You can glue up thick and reduce quickly after with your planer to near veneer.
Old boys used to take the lumber core, cross-veneer to hide and joints, then apply the primary on the good side, two of whatever on the opposite.
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GeeDubb wrote:

Gary:
First, I'm glad you made your post, I'm a couple of weeks from doing the same game board and had just assumed that David Marks was being anal. Now I assume he learned this the hard way.
On the show for the chessboard, he uses the same veneer on both sides of each strip. In other situations, he's used other woods for the backing veneer (e.g. cherry backing with madrone burl front). My guess is "similar density" is adequate.
~Mark.
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I'm also in the midst of this project. I'm using some different materials partially due to expense but also availability and quality. Our local Woodcraft had some nice Padauk so the field it that and maple. I also was warned by a friend to make sure I veneered both sides to prevent warping. As somewhat of a novice for "fine" woodworking, I can't tell similar density from a hole in the ground so I opted to do what Marks did and use the same material on both sides of the substrate. Instead of apple plywood, I just used 1/2 MDF, This seems to be working so far. My one problem was that I don't have a drum sander and I was afraid to put such thin veneers through the planer by themselves to I laminated them on both sides of the MDF and when they were dry, I jointed one side of each and then put them all through the planer. This actually worked quite well although it's obvious from a cross section that the veneer thicknesses vary a bit. I'm keeping my fingers crossed that this won't affect the warping issue.
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