Dome construction

After substantial consideration, I realized that an octagon roof would appear too 'industrial' for a back garden. In the March 2001 edition of 'Astronomy Now,' I read an article detailing the backyard observatory built by Chris Newman. He had built an 8-foot dome from plywood. This inspired me to follow a similar course. I did the trigonometric calculations, spherical geometry and some drawings and then set to work constructing it.

I had two halves of a 3m diameter ring bent from 80 x 80mm mild steel angle, a full ring is more difficult and expensive to transport. The halves were leveled and welded together and I drilled and countersunk 40 holes, which would attach it to the plywood structure of the dome.

The cutting of the curved sections of 18mm ply was very tedious and the fabrication and fitting of the thin plywood skin was extremely slow and laborious.

My wife Amanda and son Matthew.

To my surprise and satisfaction the dome came together without any major problems. The dome structure is very strong and the thin ply skin when bent becomes surprisingly rigid. To prepare the top of the base section I had to fit some 18mm ply flat roof sections around the edge and a circular upstand to prevent rainwater running inside. The dome and flat roof sections were waterproofed using a high quality glass fibre reinforced roof coating. Eight 100mm heavy-duty rubber tyred rollers were fitted for the domes steel base ring to rotate on. The dome now had to be lifted on to the observatory base structure. I calculated that with the shutters removed it weighed at least 215 kilos.  

I arranged for 7 friends and neighbours to gather together one Saturday morning. They were promised some beer in exchange for 10 minutes of their muscle. Eight of us proved to be only just strong enough to lift this large heavy structure about 15 metres into position, 10 or 12 people would have been safer. The dome fitted perfectly on the eight rollers and precisely around the weatherproofing upstand, which I new would be tight.

Inside, I fitted four adjustable lateral positioning rollers and four locking bolts to hold down the dome in high winds. Domes tend to withstand high winds well, since a wind from any direction should push the dome downwards.  Moreover, this dome is rather heavy. That said, I feel safer with the locks in place. I fitted a bright flood lamp on a dimmer switch inside the top of the dome and a 15 watt red pygmy bulb in each corner hidden from direct view shining light downwards also controlled by a dimmer. A carpet was fitted to the floor and a burglar alarm was fitted.

Base construction << Previous page   Home   Next page >> Equipment