Q: We use a long, slender piece of wood (pool cue) that must be perfectly straight and stay straight. How can we do this?
A: Wood has three basic directions, with properties that vary in each of these directions. The directions are tangential (parallel to the rings when looking at the end grain), radial (across the rings), and longitudinal (along the length of the lumber or vertical in the tree). To minimize warp in a very critical product, the first step is to make sure that the piece you have is perfectly aligned with the three directions. In other words, if you split the piece lengthwise with a wedge starting at one end, the split would go down the entire piece and not deviate to the side. We would say then that this piece of wood has zero slope of grain (SOG=0). Because of this grain alignment, it will not warp when the moisture content changes, except in very rare cases.
How do we get the grain aligned so perfectly? When sawing the piece, we first split the log into smaller segments. The split faces will be parallel to the grain, and so we saw the small pieces parallel to these split faces. Having said this, if you are really alert you will recognize that when you split the wood, there are actually two directions that you need to split - tangential and radial alignment - to make sure that the piece is right at zero SOG in both directions. This is why you cannot just use a quartersawn board for zero SOG because quartersawing only aligns the radial direction. Does zero SOG sound expensive? You bet! But for an expensive product that must stay straight, it is worth the effort.
Have something to say? Share your thoughts with us in the comments below.