Pinewood Derby Car Tutorial, Slide 18
Using a file and 100-grit sandpaper, remove the remaining corners and create a smooth curved surface. Carefully look at the shape from different angles to detect flat spots and asymmetries. Run your fingers over the surface to find places that don't feel right because they are flatter or more curved than they should be.
Once you are happy with the shape, sand the entire car with 150-grit and then with 220-grit sandpaper. Wipe the surface with a damp cloth. Let the block dry for a few minutes. The surface will feel slightly rough. Sand it again lightly with 220-grit paper, just enough to remove the roughness.
[As an aside, if you happen to be interested in computer graphics or computer-aided design, you may have noticed that refining the surface of the car by cutting off the corners and edges, as shown in the previous slide, is the real-world equivalent of constructing a subdivision surface in the computer. The original edges and corners are the equivalent of the control mesh, and cutting all of them off corresponds to a subdivision step. Cutting off all the new corners and edges that were produced in the previous step constitutes another subdivision. An infinite number of subdivisions produces a completely smooth limit surface. The limit surface tends to have a pleasing shape without unwanted creases, flat spots or abrupt changes in curvature. Of course, in the real world two or three subdivision steps is about as far as you can take cutting off corners with a chisel and a plane. After that you have to switch to a file and sandpaper.]
Pinewood Derby Car Tutorial, Slide 18
Using a file and 100-grit sandpaper, remove the remaining corners and create a smooth curved surface. Carefully look at the shape from different angles to detect flat spots and asymmetries. Run your fingers over the surface to find places that don't feel right because they are flatter or more curved than they should be.
Once you are happy with the shape, sand the entire car with 150-grit and then with 220-grit sandpaper. Wipe the surface with a damp cloth. Let the block dry for a few minutes. The surface will feel slightly rough. Sand it again lightly with 220-grit paper, just enough to remove the roughness.
[As an aside, if you happen to be interested in computer graphics or computer-aided design, you may have noticed that refining the surface of the car by cutting off the corners and edges, as shown in the previous slide, is the real-world equivalent of constructing a subdivision surface in the computer. The original edges and corners are the equivalent of the control mesh, and cutting all of them off corresponds to a subdivision step. Cutting off all the new corners and edges that were produced in the previous step constitutes another subdivision. An infinite number of subdivisions produces a completely smooth limit surface. The limit surface tends to have a pleasing shape without unwanted creases, flat spots or abrupt changes in curvature. Of course, in the real world two or three subdivision steps is about as far as you can take cutting off corners with a chisel and a plane. After that you have to switch to a file and sandpaper.]