Attention was now turned to the roof of the ‘room’ under the dome which apart from the dome itself would consist of four angular sections that would cover the area between the bottom ring supporting the dome on castors and the four corners of the square perimeter made by the angle iron frame. The shape and fashioning of these sections had been on my mind for a while.
Naturally, each of the four pieces would have to follow the contour of the base of the dome on their inner edge i.e. have a rounded edge stretching the length of a quarter of the circumference. The two outer edges of the piece would have to make a right angle with each other and extend some distance beyond the perimeter of the square chamber to allow for rain to drop off the sides. Because of the closeness of the diameter of the dome base and the sides of the room it would necessitate the angled sections to be rather narrow at their outermost reaches i.e. where they meet with their neighboring counterparts. This was rather worrisome to me as I was afraid the plywood would be vulnerable to breakages at these points, especially in the phase of construction.
Furthermore the four corner roof sections would have to show some degree of downward slope from their inner to their outer edge or one would risk the water pouring on them from all around the roof of the dome would end up finding its way inside.
Four cardboard patterns were fashioned to fill the area from the wooden ring on the inside extending out beyond the sides of the room and slope downwards and forwards as they do, so as to allow for water drainage. These were at first made to be identical but it was found that small differences existed between the four corners and minor alterations in the patterns were necessary to ensure that the four fitted in together. A lot of taping and stapling had to take place but eventually I got the four cardboard corners to match all the surfaces and the next job was transferring this to marine ply wood making use of my trusty jigsaw.
Marine ply is rather pricey here and to make the best use of the sheets I had, took a lot of conjuring and conjecture! The plywood was cut up and glued to best fit in with the shapes required.
The necessary gradient slope was obtained by raising the inner edge of the 4 corner roofing sheets on the 5mm thick metal beams that braced the square roofing frame and supported the ring at the corners. Wooden wedges were hammered between the angle iron frame and the inner edge of the corner sections to ensure this stayed higher than the outer border. These later became redundant when glue and fiberglass were added to fortify the structure and bind the four pieces together, merging them with the base ring beam. Some of the small wedges remain in place till today and from time to time slip off on their own.
The sections were reinforced with more plywood on their inside lower surface to improve their strength and help hold their shape.
… four right angles
They were all treated with generous doses of an acetone/resin 6:1 mixture with a small quantity of hardener added and further primed with wood preservative and several coats of wood primer before their final coating that was matt black below and matt white on top.