Building the internal stem
January 21, 2011 § Leave a comment
Internal stems are what the strips are attached to at the bow and stern. They can be made out of a solid piece of wood, but it’s easier to laminate several strips. These strips are bent around the bow and stern forms. When you’re stripping the canoe, the stem gives you a good surface to glue the strips to at the ends. Internal stems are also important in terms of strength and helps the canoe better handle impact.
Because the internal stem is hidden within the boat, its appearance is less important than that of the external stem. As a result, I’ve decided to experiment.
I had some strips of white cedar left from the previous build. The stock is perfect for the internal stem in that its soft and bends easily. I’ve also used pine in the past. I don’t have a steam box and don’t really feel like building one. That said, I know that cedar typically responds well to the heat gun. It’s still a little nerve-wracking to wrap the cedar around the bend of the form, expecting at any moment to hear the tell-tale crack of wood that has been overstressed.
For the first internal stem, I stack 3 knot-free strips of 1/4 inch white cedar. Instead of doing one strip at a time, I apply glue between all of the strips at once and apply heat. I gradually tighten the strips against the form, heating all the while. Just as I tighten the final clamp, I hear the wood splintering. When I investigate, there are a series of small splits in the wood on the edge where material. Because the edges will be planed off anyway, I decide to leave it.
For the second stem, I soak 3 cedar strips in water overnight. The theory is that since it’s the dead of winter, the first strips have dried out somewhat. Soaking them will hopefully allow them to absorb moisture and make them easier to bend, particularly with the addition of heat. I apply glue (Gorilla Glue, in this case) to the strips and stack them. I clamp the stack to the end form as follows…
…and add more clamps and pressure as I work around the curve. No splintering. In fact, the wood is bending smoothly and easily.
The final result looks pretty good.
Note that I’ve taped the form. This is to prevent the stem from sticking to the form. Before I begin stripping (the canoe), I’ll tape the edges of the station forms as well.
I’ll let the stems dry before planing the edges and mounting the end forms to the strongback.