Tuesday, November 25, 2008

Woodworking in America: Medullary Rays

One of my big take-aways from the conference was learning about the medullary rays in trees, a topic addressed in the session on wooden planes with Don McConnell and Larry Williams from Clark & Williams Planes and Roy Underhill. Brian Boggs also talked about medullary rays in his seminar on understanding wood for chairmaking.

The medullary rays are wood fibers that run perpendicular to the grain. They are what gives quartersawn white oak the flecks that are integral to the beauty of Arts & Crafts furniture. With the flecks, you are seeing end grain, which is darker in color than long grain and causes the contrast.

In a tree, the medullary rays help stabilize the structure and allow moisture and nutrients to flow back and forth, while the grain of the tree allows the moisture to flow up and down. Generally speaking, all trees have medullary rays, though they are more pronounced in some species than others. Medullary rays start in the center and run straight out like the hands of a clock.

They stabilize planes in the same way they stabilize trees. For planes, which are also often made of quartersawn lumber (Beech in the case of Clark & Williams planes), the medullary rays help distribute moisture from one side of the plane to the other. This effect helps keeps the wood stable as it counteracts the effect of the moisture running the length of the plane through the end grain.

Brian Boggs spoke about medullary rays in the context of finding parts of the tree that serve different functions as parts of a chair. My memory on which parts go where is a little sketchy here, so if anyone who attended that session can fill in the blanks, please comment. All that said, I'm going to dive in and do a bit more research to understand this stuff better.