Next a full length of flat bar was given a curve using the bending jig. Handling a curving 6 meter long flat bar on my own proved a rather daunting task and called for a lot of (often comical) improvisations. The iron snake seemed to have a mind of its own and was not going to give in without a fight!
The full 6 meter long flat bar fell short by a little bit from completing the whole circuit and had to be lengthened by a small stretch which was later carefully welded at both ends and filed down to provide as smooth a transition as possible.
The completed ring was then wedged well into the routed channel and held in place by several anchoring low-profile clips designed for the purpose and arrayed all around the ring.
An order for an assortment of steel sections and galvanized metal sheeting was made and the day after ..the crane arrived.
..and the Iron Curtain falls
..from that day on and for about a year my workshop became rather crammed and at times I had hardly room enough to squeeze my way to the door..
Next I welded a square frame of 5 cm wide angle that would serve as the metal support for the wooden circular base on which the castors would be arraigned.
This would also define the perimeter of the roof of the observatory and serve as a convenient frame to work on during the construction.
For this purpose a set of four short ‘legs’ cut from the same angle iron were bolted to the four corners converting the frame into a low table. To improve support of the circular beam four sections of angle iron were welded at the corners converting each corner into an isosceles triangle and the metal frame support for the doughnut into an octagon.
With the circular roof beam bolted and the whole checked for horizontal by spirit level, the mating ring of double plywood that would form the base of the dome was placed over it and the two clamped together to make sure they matched perfectly. The router jig was placed over the top one and a circumferential channel about ½ inch deep routed along half way the width of the beam. This formed a gutter for the flat bar that would form a metal rail to glide over the castors.
Several sheets of ¾ in plywood were purchased and construction started with the fashioning of two rings,
each made up of a double layer of plywood sandwiched, screwed and glued together.
Trying out the doughnut
Care is taken to avoid end joints from overlying others. This is automatically prevented by displacing the top segments by about half their length.
The double layer of wood would provide the base support for the dome and a rail-on-castors system for enabling axial rotation of the dome.
The dimensions of the rings i.e. their width and radii were worked out from scaled models.
Having sandwiched the two layers of plywood together to form a 1½ ” thick beam, a length of 2″ x 1″ was clamped at both ends exactly over the diameter and another shorter length pivoted through its center like the minute hand of some giant clock. To this was attached the router harness in such a way as to allow careful final trimming of the inner and outer circumferences of the ring and result in an even curve.
As the metalwork would surely entail a certain amount of bending and curving it was considered essential to provide some sort of reliable metal shaping gadget and this was the end result…crude but proved very useful.
Steel section bending jig
This jig was made out of bits and pieces of leftover channel and three roller bearings. A section of tubing was welded to the central one to allow for a “handle” to be attached. The jack handle controlled the bending force and the round bar with the black knob attached was linked to the release valve . Although ideally best suited for bending round bars, it managed to do the trick with flat bars too, requiring a little patience and frequent realignment of the bar being fed to prevent slipping and/or warping.
The bending force was provided by a car jack I had lying around.
Various plans were considered and one of the earliest was that of a geodesic dome. Some models were tried out.
While this looked like providing a reliable way of producing a spherical structure, its construction in metal was thought to require a large number of joints and also its rigidity would be further compromised by the need for opening up the window apertures required. For a while I pondered on using wood or fiberglass but I am more at home with steel and somehow I find it easier to manage.
Finally it was decided to build a dome made up of 16 vertical sectors made from galvanized steel sheeting.
I was still unsure as to the best way to support these segments internally and this is where I found the ideas and descriptions of other enthusiasts like John invaluable. But the final decision had to wait until the project was already well underway. After all, a lot needed to be done and materials assembled before it became necessary.
After lengthy browsing of internet resources and weighing up pros and cons as well as the inevitable monetary considerations I decided that my new OTA would take the form of a Celestron 8 ” SCT on an AVX mount. This comes complete with a rigid and chunky tripod suitable for mobile field work but of course I was already planning on a more permanent fixture.
Still, until such time as this was available the telescope on its mount and tripod ventured out on the roof on many an occasion and instantly proved its worth with the AVX taking over control from my not-so-nimble fingers. The ‘Go To’ feature and the 40,000 objects on the mount’s database meant that literally the Cosmos was my oyster! It proved a very good teaching aid, familiarizing me with the location of celestial objects and their apparent spatial relation to each other.