Chapter 2, Lesson 4 of 4
Learn how to process boards with cathedral figure and remove or avoid
distortions that are common with this grain pattern.
Boards exhibiting cathedral figure may be attractive to you, but that
rippling grain effect requires some care to harvest parts from it
successfully. This lesson will provide you with some pointers on how to
avoid or remedy the most common problem with cathedral grain: cupping.
|Although the cathedral figure is beautifully defined on this board, it's neither centered in the board nor straight with the edges. Use a chalk line to get the geometry right. Center the hook at one end, hold the other end to center, and snap the line. Measure to the nearest edge of the board, then measure the same distance on the other side of the line at both ends.
You will decide which end will give the best figure for the length and width of the part you need. If the harvested board is not wide enough, search for some straight-grained, riftsawn, color-matched material and glue a piece on each side.
The result is what would have been there if all trees were made perfect!
The first and last boards that come from a plainsawn log normally have
cathedral figure - it's the grain that looks like the undulating ripples
of a pebble tossed in a pond. Boards with cathedral grain are the most
prone to cupping. They will always cup away from the heart of the tree.
That's because the tissue on the top half of the board is more
tangentially oriented than the tissue on the bottom half. So shrinkage
is greater on the top half, hence the cupping.
If the cupped board has a moisture content of 8% and you can flatten it
by jointing and planing to get the thickness you want, it's not likely
to cup again. So use it for its beauty and don't worry about the
likelihood of distortion.
If it's cupped more than can be removed by a jointer/planer, the
solution is to saw it down the center of the cup, flatten the two
boards, and reassemble with a butt joint. You don't have to flatten the
two pieces individually. They can be reassembled in alignment, then
flattened - same difference. You will hardly be able to detect the
material missing from the center, especially if you saw with a thin-kerf
In a badly cupped board that's worth saving, saw it into three pieces to
reduce the effect: the narrower the boards you saw, the more you reduce
|Look at the edge of this cathedral-grained board. The severe angle of the grain to the face of the board is called short grain. A rail made from this, if stressed, would be prone to breaking along the short grain. Consider this firewood, not furniture wood.