TECH TIPS PAGE TWENTY ONE
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Building Tip - More on Miniatures by Ted Behne
Previous articles outlined the process for selecting a canoe to model, reducing its dimensions to one-quarter scale, making a "blueprint" of the canoe, constructing a reusable building platform, making a gunwale frame, making thwarts and installing them. This article will focus on splitting cedar, an obscure but important skill that underlies many of the steps in making a birchbark canoe.
The wood is Northern White Cedar (Thuja Occidentalis) and it's pretty amazing stuff. It is light, easily carved, bends well and is naturally rot and insect resistant for decades with no weather protection. For canoe building, only the creamy-white wood in the middle of the tree is used. The darker sapwood, growing nearest the bark, is too weak and does not bend well. The heartwood at the center of the tree is prone to decay. Both the sapwood and the heartwood should be discarded.
One of cedar's major assets as a canoe-building wood is its tendency to split smoothly along lines of grain. Indeed, in the hands of someone who is skilled at splitting cedar, it can be difficult to distinguish split wood from a similar piece that has been planed and sanded. But more importantly, split cedar is stronger and bends more reliably than sawn cedar. That's because sawing cuts through the lines of grain and significantly weakens any component made with the wood. Many old museum canoes are so well built that they look as though they were made with power tools. Much of that smooth finished look comes from the builder's skill with a crooked knife, but creating the rough blanks to make gunwales, ribs, sheathing and headboards comes from the builder's skill with splitting.
So what's the secret? How does a novice learn to split cedar like a pro? The same way you get to Carnegie Hall: practice, practice and more practice. Theoretically it makes no difference whether the cedar is wet or dry. It should split equally well, if it's fresh. But in practice I have found that wet cedar splits more reliably and more easily than dry cedar. Cedar splitting is a particularly valuable skill for making sheathing blanks. Good quality cedar can literally be split down to a single growth layer - only a few thousands of an inch thick - so thin that it looks and feels like paper.
Start by soaking the cedar overnight. Then mark a line at one end of the rough blank to begin the split. Start the split with any sharp blade, and then "wiggle" the split open enough to allow fingertips to take over the work. Ideally, the split should be made in the exact center of the blank. The centerline approach equalizes the stresses on both halves of the split and requires only that equal pressure be applied to both sides. But if a split begins to wander to one side or another it can be moved right or left of center simply by applying a heavier "pull" on the wood in the direction you want the split to go. To get sufficient "pull" to move the split line one way or another you may have to jam the cedar blank between two table legs (or your own legs for that matter) to get sufficient leverage. This "pull" phenomenon can also be used to maintain an off center split from the beginning, such as when removing a sapwood strip from a larger chunk of wood.
Try both methods until you master them. You will ruin a few cedar blanks, but the skills you will acquire from the practice will serve you well for many future projects. Next, turn your attention to making ribs, the essential skeletal structure of the canoe. That process will be described in next month's newsletter.
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