The dome

Your telescope really needs room to move in the dome and depending on how many people you wish to share the skies with. Your telescope also needs plenty of clearance for people to move around it in the dark without bumping it or tripping over things. (A dim red light inside will also help.) My 12 inch Celestron is fairly short, but quite bulky with all its attachments, so I want to be able to move freely around it.

My plans have changed from a 4 meter high dome from ground to apex, to a 3 meter high dome with a 1 meter sunken front entrance and back to 4 meters again. This is because of local land authority restrictions on class 10 outbuildings on private property. Look up your local authorities before you build anything. The Photo below is the plan. It looks simple enough but I think there will be plenty of challenges. God will help me no doubt.

The 110 triangles that make up the hexagons and pentagons that form the dome are made from 5mm plywood, scored from equipment packaging boxes.  I cut 48 triangles in 2 nights after work with a jigsaw. I don't know if it's the cold or my back that eventually stops me. Patience is the key here. Before you decide to build in plywood, think about cost of  whatever you are going to coat it in to make it weather-proof and secure from potential break-in. The area of the outside surface of the dome is about 17 square meters, including allowance for a little wastage. 

I tried a couple of ways to join up the triangles to form the polygons. A trip to the hardware stores proved that aluminum or any sort of thin metal was prohibitively expensive. I purchased a roll of embossed plastic that seemed thick, flexible and durable enough. I just hoped that liquid nails would bond it to the wood properly. Unfortunately I don't trust glue. Never have. It proved to be time consuming and not strong enough anyway. I was so exasperated to have come this far after deliberating for so long on what to make this darn dome out of.

After a night off, I thought God would provide a solution if I asked in His own good time. The following day, my prayers were answered. The solution cost me nothing either. Some metal strapping from the scrap bin at work and some small hexagons and pentagons cut from the scrap plywood screwed in the centre. Make sure you get a good supply of screws, (500 should do it). They should be long enough to get through the ply, biting in past the taper. You can angle-grind the sharp protrusions off later or fibre-glass over them if they are short enough. 

Joining the polygons together  was a little slow at first but then the next door neighbor, God bless him, came over to lend a hand. You really need a second pair of hands for this part of the job. When he left, my brother in law took over for a while. God and his timing. It went together so well and the speed of it astonished me.

To join the polygons together I used the same method of steel strap bits and ply hexagons in the joins. Only this time I used glue under them as well as screws for added strength and peace of mind. In hindsight I should have used glue (liquid nails by the way) under all of them. On other sites I have seen people put the dome together from the bottom up, but I started in the top centre, turned upside down at first, and worked my way down. Make sure you turn it over before it gets too heavy or it may break.

Once you have all the polygons joined together, you can remove the metal straps, as the dome is now held together at every joint by the little plywood polygons. You will find it is also very strong! The geodesic design is one of only a few architectural structures that actually gets stronger, the bigger it gets. Any gaps left in between the wood, I used an acrylic poly-filler, so that later the fiberglass will have a surface to bond to instead of going over a gap. If the gap is large you can put some tape behind it until it dries. If the gap is huge you can cut a thin strip of ply to fill it. If you have too many very large gaps, you may want to re-think going ahead with the dome at all. Pulling it apart and starting again may be the option there.

For easy calculations on triangle dimensions for different sized domes, go to this site www.desertdomes.com/domecalc.html it is an excellent calculator. All you have to do is enter in the dome size and select whether you want it made out of a few big triangles, or lots of small triangles.