Dry wafers on disks
November 10, 2011 | 6:00 pm CST

Q: How can I dry wafers or disks from a tree so I can make round tables about 3 inches thick? My first attempt resulted in some very large cracks that made the tables unusable.

A:  The concern with large disks is that they will split (one large crack and perhaps a few smaller ones) no matter how carefully the wood is dried. The species that shrink a lot (oak, beech, hard maple) will have more problems with large cracks than the lower shrinking species (basswood, soft maple). There is a procedure in Drying Eastern Hardwood Lumber, US Dept of Agric. Handbook No. 528. (This book is at all large libraries and can be obtained at smaller ones through interlibrary loan.) The procedure, which involves making a paste out of egg whites and salt, was used on a historic elm tree here in Madison, Wis. It worked on most of the pieces. Coating them with polyurethane, or even acrylic, is possible.

An alternative, then, is to dry several disks (#1 through #5) but before drying put a saw kerf in each disk. This will make the crack develop where you want the crack to occur. Each kerf should be in a different location in each disk, one at "noon," one at 3 o'clock, one at 6 o'clock, etc. Then, when dry, cut out a wedge from the disks #1, #2, #3, #4, etc., with this wedge containing the saw kerf crack. Then, go to disk #5 and cut wedges out of uncracked wood at the correct location so when wedge #5 is put into the hole in disks #1, #2, #3 and so on, the wedge will match the hole perfectly with the grain being almost perfect too! Just kerf each disk in a different spot, so that the wedges from #5 will fit. Clear?

There is a chemical called PEG (Polyethylene glycol-1000, a relative of antifreeze) that can be impregnated into green wood. When the wood tries to shrink during drying, the PEG prevents shrinkage. One key requirement with PEG is that the wood must be porous so that the PEG goes deeply into the wood. Elm, white oak and many other species containing heartwood probably will not be porous enough to get good treatment.

Another possibility in some situations is to drill a large hole in the center of the piece before starting to dry the disk. This hole will give the wood room to shrink. In all cases mentioned above, the disks should be dried quite slowly.

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.