I received this question in episode 4 of the Ask Brian Boggs Show:
I assume you use wide boards for many of your projects. How do you prevent wide boards from warping? I realize selection is important, but are there any other ways to prevent warpage?
There are many ways to prevent warping nevertheless selection is critical. Selection for us, means beginning at the log yard where we look at the grain in the bark. We look for logs that do not have an abundant medullary twist. For the most part, trees will have certain quantities of wind, which results in their grain not growing in a straight line from the ground up to the branches. What happens is the grain grows more into a slight spiral, which usually develops into a right-hand screw shape in the northern hemisphere of the world. Now, on the southern hemisphere (below the equator), I believe trees develop a left-hand screw shape. In both situations however, the grain will spiral downward. The more it spirals, the more twist and warp the tree is going to develop. This is one way to avoid various problems.
In cherry lumber it is nearly impossible to see this. This is a good reason to purchase logs instead of lumber. Walnut, oak and more coarse grain woods will usually get flat-sewn board on the edge. For quarter-sewn boards you will see this more on the face, even on the edge. This clearly shows the grain direction. When viewing the boards pay careful attention, and try avoiding, one that have wind in the grain. This will prove to be very useful. If you are dying your own wood, you will want to gradually dry as well as keeping it weighted. This will help alleviate some of the stress that will cause boards to begin warping later on. However, most boards do inevitably warp to some extreme depending on diverse factors (ie. moisture content). Wood will continually swell or shrink. To help minimize this, bolting them down is always a good procedure. Bolting the boards to a cross member is a necessity – either by trestle table or a four-legged table.
ou need to make sure to have a secure bond in order to keep the wood from lifting off the frame by using enough of the movement allowance in the screw attachment as to keep the wood from traveling laterally because of shrinking and swelling. I say this, but as a note, wood will eventually travel; however, you can slow its movement by placing a great deal of finish to the surface.
On that note, I would like to add there is one method I thoroughly enjoy which helps ‘almost’ eliminate movement, shrinkage, warping and cracking. We call it an Engineer Top. This method requires using a thick birch ply core and a band-saw veneer application. This will give you the beautification and integrity of the solid wood top while maintaining the stability of the plywood. Plus, in my view, it really is a great solution. This helps opens up options for designing table bases and other pieces of furniture in a market where solid wood demands a mechanical and structural way of keeping boards within the furniture flat (traditional furniture is always addressing this issue).
Engineered panels, whether tabletop or cabinet sides, using ply core and band-sewn veneer face typically eliminate the issue and also open cleaner design options. Let me finalize by saying, ‘cleaner’ means ‘parts’, which simply are used to maintain flatness of the surface. This task is taken care of internally within the other panels.