TECH TIPS PAGE SEVENTEEN
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Creating the 1/4 Scale Building Platform
The last issue outlined some of the preliminary steps in making a scale model birchbark canoe. Selecting a canoe was discussed including the importance of carefully reducing its dimensions to accurate scale. A procedure was presented for preparing a ¼-scale "blueprint" of any of the canoes depicted in the Adney and Chapelle book, "The Bark Canoes and Skin Boats of North America."
This article will deal with how to make a quarter-scale building platform that can be reused over and over with many different styles and sizes of model canoes. As with all other aspects of building model canoes, a building platform should be made just as it would be for a full-size canoe, using the same materials and the same techniques, only scaled down to smaller size.
A full-size building platform consists of wooden planks, about two inches thick, at least a foot wider than the canoe to be built and several feet longer at each end. It is crowned up to two inches higher in the middle than at the ends, to help control the amount of rocker in the finished canoe. A full size platform is typically about 20 feet long and about four feet wide. Reducing the dimensions for a quarter scale model yields a model platform that is five to six feet long, about one foot wide and a half-inch or more thick. Suitable pre-cut lumber can be found in the shelving area of Home Depot and most other building supply stores.
To make my model platform portable, I fastened it to an extra tall sawhorse that I built especially for the purpose. I screwed down one end of the platform to the sawhorse, then positioned a 3/8" dowel, widthwise, (more about this later) under the exact center of the platform before I screwed down the other end. The resulting building platform is slightly crowned in the middle, which helps to control the amount of rocker in the finished model. I made the sawhorse extra tall to work either sitting on a stool or standing up.
In a full-size canoe, stakes are pounded into the ground to hold the bark upright while it's being lashed to the gunwale. With a model, I use 3/8" diameter dowels as "stakes." I drill slightly larger holes into the building platform and insert the stakes into them to hold the bark in place.
I buy 3 ft long, 3/8" diameter rods at Home Depot and then cut them up into the various lengths I need to hold the model in place. The "stakes" at the bow ends are about 8" long and the ones nearer the center are about 4" long.
If the building bed is flat, the resulting canoe can develop more rocker than is wanted. If the building bed is crowned in the center, the amount of rocker in the finished canoe will be reduced by the amount of crown at the center. More crowning equals less rocker, less crowning equals more rocker. Each canoe requires a separate decision about rocker and crowning. A typical full-size canoe with moderate rocker would have about 1 1/2" to 2" of crown at the center of the building bed. At one-quarter scale the measurement becomes 3/8" to 1/2". A 3/8" to 1/2" dowel inserted widthwise under the center of the building platform serves the purpose perfectly.
Next issue will cover other preliminary steps such as measuring and making scale-size thwarts, gunwales, ribs, sheathing, pegs and roots for lashings. These preparation steps constitute about half the total construction time for any canoe. They can be done at your leisure, with no particular timetable, and stored until you are ready for assembly. It's relaxing and rewarding to see steady progress as you complete one component after another. If you are hesitant because you feel you may not know enough to do it right, I will be happy to coach you through the step-by-step process at no charge.
More on Miniatures by Ted Behne
You can view it here.The crown in the middle of the building bed helps control the amount of rocker in the finished canoe. When ribs are forced into the center of a canoe, they stiffen the gunwales and lift the ends off the ground. This rising profile at each end is called the "rocker" of the canoe. Some canoes need a lot of rocker, i.e., those designed to run rapids or to slice through ocean waves. Others need very little rocker, i.e., those designed for use on flat water.
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