Replies

1. 
   scott_murray | Mar 04, 2002 06:18am | #1

   *
   Billy
   The usual practice when doing laminating is to place a lamination of the same (or similar) wood on the back (or under) of the substrate as well. This stablizes the substrate and (guess what) reduces the risk of cupping.
   The second part of your post is a different matter. The movement of wood when you cut it is a reaction of the stress or tension in the wood itself. Cut your piece a bit big, four square it close to your finish dimensions, then let it sit for a few days to stabilize. Then bring it to final dimensions and it should be okay.

   Scott Murray

1. 
   Jon_Arno | Mar 04, 2002 06:44am | #2

   *Billy, it sounds like the piece of yellow pine may have had a case of "case hardening", resulting from the way it was kiln dried (the drying stress was not relaxed late in the kiln process, which is often the situation when the wood is dried for construction, rather than cabinet making applications.) If you had planed down the yellow pine first, taking equal amounts off of both faces before bonding it to the walnut, you might have avoided most of the problem. Even so, it is a risky proposition to bond two different woods (of the same thickness) together. They will function like a barometer, if their shrinkage characteristics are especially divergent. It is better to design the project so that the more stable species dominates. It will then function much as the substrate in veneering. Another helpful precaution is to bond the members so that their end grain is convex to the outer surfaces. The members will then have a tendency to want to separate at the center where the bond should be the strongest and thus able to prevent either from cupping.As for why your other walnut stock is distorting, do these pieces contain the pith of the log?...Or juvenile wood tissue (immature, sapling wood from close to the center of the tree) on one face? Walnut is usually very stable, and while it is possible to screw it up bigtime with a poor kiln drying schedule, unless one of the above situations prevails, it normally doesn't distort.

1. 
   Jon_Arno | Mar 04, 2002 04:31pm | #3

   *Barometer? I meant hygrometer, of course. Thermostat would have been another good example, except it's based on heat...where two metals with dissimilar shrinkage properties are bonded together and bend in response to a change in the temperature. Woods do the same thing, except in response to changes in humidity...Anyway, Scott's solution of a third ply on the back would also help to prevent distortion. It might even be a way to fix the problem, if the current cup in the drawer front will come out under clamping pressure.

1. 
   Mike_Taylor1 | Mar 04, 2002 05:43pm | #4

   *Gluing two dissimilar woods together is usually an invitation to trouble. I've put a lot of fronts on drawers, but always used 4 screws from the back. An advantage to that is they can be replaced later. Never done it with 3/8" thick stuff though.