Replies

1. 
   mapleman | Mar 26, 2007 08:26am | #1

   Paul,

   It would  really be best to cover the opposite side with a veneer of similar thickness as the front. It doesn't have to be the same species (walnut in your case). I would recommend against using hardboard or plywood. You want to treat both sides of the panel the same to minimize any warping issues.

   Good luck and let us know how it turns out.

   Lee

2. 
   JohnWW | Mar 26, 2007 02:12pm | #2

   Both sides should be covered with a veneer of real wood, with the grain running in the same direction, and with a somewhat similar rate of movement. 

   At 1/8 inch thick, the veneer is going to act like solid wood and possibly develop cracks when attached to a plywood backing.  You could just saw the walnut to 1/4  to 3/8 inch thick and skip the veneering.

   John White, Shop Manager, Fine Woodworking Magazine

    

1. 
   AdamCherubini | Mar 26, 2007 02:30pm | #3

   Does anybody know what the problem is, John?Is it the moisture barrrier of glue? Would the sme thing happen with a high pressure laminate? Or the differential movement of two different woods? What if he chose MDF as the substrate? What would happen then?I've got veneers on pine 4/4 x 12" x18" or so samples in my shop. The boards were flat when I bought them, flat when I veneered them, and have remained thus. I veneered the heart side. What should I expect to see?Adam

1. 
   JohnWW | Mar 26, 2007 02:59pm | #4

   The plywood core won't expand and contract with moisture changes and the veneer will.  If the veneer shrinks when exposed to drier air it will cause the plywood to cup just as though you put a bar clamp across the plywood panel and tightened it.  By placing a second veneer on the back side of the plywood, the two veneers fight each other and the panel will stay flat.The closer the match between the movement characteristics of the two opposing veneers the better the chances are that the panel will stay flat. 

   If you are working with plastic laminates, it pays to laminate both sides of the core, there is a cheaper thin "backer" laminate actually sold for this purpose.  You can't back a wood veneered panel with a laminate since the two have radically different reactions to moisture.

   The problem has nothing to do with the glue used and will occur to a greater or lesser degree with any core material.

   As to the samples in your shop, are the veneers going cross grain to the solid wood core and have they been exposed to a dryer or wetter environment since you made them?  If the samples haven't gained or lost moisture they will stay flat.

   John W.

2. 
   Buster2000 | Mar 27, 2007 01:51am | #5

   Adam,

   I found this Faq over at Joe Woodworker.  Interesting veneer stuff:  http://www.joewoodworker.com/veneering/faq-veneering.htm

   Anyway their claim is that the water in the glue causes the cells in the veneer to expand.  As the glue dries the cells shrink again, and will warp the board if not counter balanced by wood on the other side.

   I suspect that John is correct, thicker veneers on a man made sustrate will warp since the veneer continues to act as wood.  Thin veneers on the other hand can be somewhat 'tamed'.

   In your case I assumed you used more 'traditional' veneering techniques.  I suspect that hide glue does not have the same water content as modern glue.

   Buster

3. 
   cadiddlehopper | Mar 27, 2007 03:03am | #6

   GotAll,

   I like John White's suggestion of making solid wood panels rather than veneer that is so thick. The finished product seems to be wasteful of a precious wood as well as your time. It is also risky. I have used veneer about 1/10-inch thick. I will never make it that thick again. You may be doing this because your planer limits the thinness of the wood. I found that a drun thickness sander works much better than a planer and can produce material much thinner. In fact, the panels may be veneered rough side out then sanded smooth.

   Cadiddlehopper

4. 
   oldusty | Mar 27, 2007 05:11pm | #7

   Hi Paul ,

              If your panels will reside in a frame , the frame won't let the panels warp to any significant amount , regardless of the exact composition .
   Assuming all components are dry .

      The entire frame would also have to warp , it's not going to happen ,imo.

    Now if you just let those panels exist with no frame to keep them flat , even a solid wood panel can warp without a frame around it .

    Try a frame and panel mock up like a small door and see for your self , especially if the frame and panel assembly is glued and attached to the cabinet there will be insignificant movement in the frame and panel in general .

           Table tops and other pieces that get veneered that may not be glued into place or permanently fastened down are much more vulnerable to warpage caused by an off set center of moisture content .

                         good  luck            dusty