What is flatsawn and quartersawn lumber?
One is a cut parallel to the radius of a circle. The other is a cut across the tangent, i.e., at a right angle to the radius.
Quartersawing is like cutting the log into pie shaped quarters and either cutting smaller wedges or rotating to cut parallel to the prior cut, to get one board.
The other method, which only yields a partial radial cut, is to cut the pie shaped quarter up parallel to the radius.
The type of cut depends on your purpose. Certain joints, such as a miter joint, are best made with radial cut lumber.
Usually when I need quartersawn, I buy rift and quartered, which is cost and materials conscious. You get some with growth rings at 90 degrees to the width of the board, and some with the growth rings at a slight angle to the width of the board. Rift is sometimes called comb grain, as if you dragged a comb with paint on it along the length of the board and made vertical lines on it.
Gene Wengert, forum technical advisor