Tophat Kiln Layout Directions
This method uses the fact that a circle can be easily divided into 6 equal parts by using the compass setting that drew it to strike a series of arcs starting anywhere on the edge and advancing the pivot to the crossing points created by these strikes until you have gone all the way around the circle. Try it first on a sheet of paper to clearly understand what you are about to do.
The reason we use this method to create the pattern board rather than a protractor is accuracy. The compass method is absolutely accurate when performed correctly. In contrast, a protractor , especially a small one, generates parallax errors that add up to a rather poor result on a project this large.
You will need:
a sheet rock nail
20" of black annealed wire (often used to tie rebar together)
a sharp #2 pencil
a 40" x 40" piece of 5/8" or 3/4" AC plywood
1. construct a compass made of the sharp pencil, the nail and the wire wound as shown.
2. set the nail at least 20" in from the edges of the very smooth, flat piece of plywood.
3. adjust the wire until the pencil scribes a circle 14.25" in radius (28.5" DIA).
4. use a straight edge to draw a single line that passes through the center. Mark the two places it crosses the circle.
5. set the nail at one of the cross points and swing it left and right to obtain two more cross points.
6. on the other side of the circle, repeat step 5, obtaining two more cross points. This divides the circle into 6 sections.
7. use a standard bow compass to draw 12 new arcs as shown above. Where these cross represent the other 6 sides needed.
8. draw lines through the center connecting the rest of the cross points creating 12 equally spaced rays.
9. place a framing square on a ray where it crosses the circle and draw a line first left, then right.
This is the inner face of the brick. Repeat this step for each of the 12 brick faces creating a 12 facet figure.
10. lay the precut bricks on the board so that their inner faces match the inner guide lines.
11. trace the outside of the bricks and trim the board to match the layup as shown.
12. this pattern board is also used to layup and construct both the base and the lid to the kiln.