When the tank is properly positioned, run intersection of the a pencil around its plywood's center line and circumference to trace its the tank's circle. Bend outline on the plywood. the flashing slightly to Now you're ready to follow the actual draw the actual cusp. involute pattern, and You'll need three feet of make a pencil mark thin, flexible wire (don't where the flashing ends use string, which could on the involute pattern. stretch and deform the This mark is the shape of your cusp), and "flashing layout line" a heavy, black pencil. that will be used in a Tightly tie one end of the later step. wire to the pencil near its The last step before point, and then position actually cutting out the the pencil's point as involute pattern is to shown in the illustration. mark the location where Wind the rest of the wire the tank support around the tank in a clockwise direction, and rackets will be mounted: Cut the center support Take one of the four tank and both sheets of support brackets and hardboard to length. Above The cusp's center it five inches to Because each hardboard original sharp angle the right of the will form half of the must be altered to 90 plywood's center line; curved reflector area, the degrees so that a square place another one five width of each sheet must 2 X 2-inch "reflector inches to the left. equal half the perimeter center support" can be Position the brackets so of the involute curve. used as the backbone of that they're square to the However, as Illustration the assembly. In later plywood's factory edge, D shows, one of the steps, aluminum flashing with their inner corners hardboard sheets will will be added to recreate just touching the tank's overlap the other by 1/8 the initial shape of the circle. Mark this location inch, so one of the sheets cusp. for future reference. must be trimmed by this That's it. Now you're amount. Use a tape Building The Reflector ready to put your pencil measure or a length of marks to use. wire to measure the Now (at last) you're length of one half of the ready to begin some Cutting The Involutes involute curve (the actual construction, distance along the adding the top cleats, Take the sheet of perimeter between the
When the tank is properly positioned, run a pencil around its circumference to trace its outline on the plywood. Now you're ready to draw the actual cusp. You'll need three feet of thin, flexible wire (don't use string, which could stretch and deform the shape of your cusp), and a heavy, black pencil. Tightly tie one end of the wire to the pencil near its point, and then position the pencil's point as shown in the illustration. Wind the rest of the wire around the tank in a clockwise direction, and intersection of the plywood's center line and the tank's circle. Bend the flashing slightly to follow the actual involute pattern, and make a pencil mark where the flashing ends on the involute pattern. This mark is the "flashing layout line" that will be used in a later step. The last step before actually cutting out the involute pattern is to mark the location where the tank support rackets will be mounted: Take one of the four tank support brackets and center it five inches to the right of the plywood's center line; place another one five inches to the left. Position the brackets so that they're square to the plywood's factory edge, with their inner corners just touching the tank's circle. Mark this location for future reference. That's it. Now you're ready to put your pencil marks to use. Cutting The Involutes Take the sheet of Above The cusp's original sharp angle must be altered to 90 degrees so that a square 2 X 2-inch "reflector center support" can be used as the backbone of the assembly. In later steps, aluminum flashing will be added to recreate the initial shape of the cusp. Building The Reflector Now (at last) you're ready to begin some actual construction, adding the top cleats, Cut the center support and both sheets of hardboard to length. Because each hardboard will form half of the curved reflector area, the width of each sheet must equal half the perimeter of the involute curve. However, as Illustration D shows, one of the hardboard sheets will overlap the other by 1/8 inch, so one of the sheets must be trimmed by this amount. Use a tape measure or a length of wire to measure the length of one half of the involute curve (the distance along the perimeter between the