Grain orientation and shape are critical design considerations in wooden planes. The best example of this is probably the coffin bodied smoother. Simplistically it seems shaped to fit the hand and there are a number of myths about the reason for its grain orientation.
We feel that the shape and grain orientation of a traditional coffin bodied smoothing plane evolved primarily for two basic reasons. The iron must be firmly forced against the bed by the wedge and the toe section of the sole must remain in the same plane with the heel section of the sole through the usual seasonal humidity changes.
It must be understood that wood is a relatively plastic material. Moisture moves through wood at a slower rate than through the air. This means that the surface of a piece of wood will generally have a different moisture content than its interior. Wood also expands and contracts according to its moisture content. The wood is usually under some stress because of this and the surface is actually deformed very slightly by this stress. This isn't a problem as long as the differential moisture content isn't too severe. We're all aware of the need to season green wood for this very reason. The thickness of the wood is an issue here...the thicker it is, the longer it takes for moisture to move through it.
We also know that water migrates through wood fastest through the length of the wood's cells. Most cells are oriented with the height of a tree and that's why we coat the end grain with an impermeable substance during seasoning. This slows moisture transfer with the air from the ends of these cells and limits the stress caused by uneven drying.
No comments:
Post a Comment