That is interesting, I have usually attributed those kinds of checking differences to different species rather than grain orientation within a species. For instance red pine, our cousin of scots pine, tends to check with many smaller checks where eastern white pine tends to relieve its drying stresses in one or two major checks. I'll start paying more attention to grain orientation and checking within a species. I don't think mild spiral is a huge deal as long as the grain within a piece doesn't become too short and weaken it. In the round the grain never "runs out" and is fairly balanced. As we saw or hew a timber we cut across the grain and also create places for the stress to concentrate as it dries. Thanks Ken, more to think about.
My experience is with log more than heavy timber, a lefty in a wall of righties is trouble, its unwrapping in a different direction from the rest of the wall and hard to keep put.
Mo,
The switch from juvenile to mature wood is gradual and in pines is normally considered to happen around the 20 year old period. Nature varies alot as does the age of a part of the tree. To drop in one more level of magnification, individual cell walls are made up of several layers of microfibrils, bundles of filaments. The S2 or middle and thickest layer of the cell wall is the one of most interest usually. In juvenile cells the microfibrils align at an angle to the upright axis of the tree, they are slanted at an angle of up to around 30-40 degrees. As the tree matures the MFA comes more in line with the axis of the tree. This is below "grain" level but I think it does have an effect on grain, or the orientation of cell to cell up the tree. I suspect this is due to the proximity of the apical meristem and its auxins. As the tip moves farther away from a section it "matures" and produces straighter alignment, further away yet and the spiral reverses. (That's all pure speculation on my part)
The MFA does affect shrinkage and direction. Shrinkage occurs as the water bound between the microfibrils leaves the cell walls. This is the "bound water" as opposed to the "free water" that is within the cell lumen and doesn't affect shrinkage as it leaves. As the water leaves the microfibrils can move closer together, this is the level where shrinkage occurs. If the fibrils are oriented vertical the wood shrinks in width and thickness...normally. If the wood has a large proportion of juvenile or reaction cells with a steep fibril angle the wood shrinks lengthwise as it dries. If a board has juvenile wood along one edge and normal wood along the other, the board bows as it dries. If the grain spirals the board twists.
