4V Steel T-Bar Dome
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These are #10 X 5/8" Pancake head self-drilling screws. The self-Tapping (drilling ) screws are needed to screw threw the connector washer and t-bar steel strut. Other self-tapping screws can be used and this structure can be built without these connectors . The reducer washers are not something you find in the average hardware store. You will need to find a contractors Electrical Supply house during week days.
An extra pair of hands is always nice to have. Drywall carpenters work with light gauge steel studs all the time and will always have adjustable C-clamps. When using your self drilling screws you must have the steel clamped tightly together. These C-clamps come in 4" and 6" sizes and with and without feet. Any locking pliers will work. A pair of tin snips (metal cutting scissors) is needed to cut the light gauge T-bar steel. A cordless drill with a magnetic Philips head screw tip works well for this project, but any drill motor with a screw tip will work.
In the Dome Kits connection system the T-bar struts will come together in the center of the 3" to 1/2" reducer washer. Center your reducer washer at the apex of the strut points. The sides will need to over lap each other so you can connect the two T-bar struts and the connector together with a screw. You will have to cut the corner off at lest one side of the T-bar strut to get the ends to meet in the center.
If you have any spherical design, engineering or building code questions please send us an e-mail and we will try to reply as quickly as possible. info@sphericalstructures.com

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All your T-bar struts will be cut square or flat on the ends to proper length. During the construction you will cut the 30 degree angle off one side of the corner to create a tight fit and meet in the center of your connection. You will find one screw in the center of your strut will hold securely since all the struts are holding each other in alignment. This is your completed connection on the inside of the geodesic structure.
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For the outside connection you can use a larger reducer washer than you used on the inside. A 4" to 3" works well to center itself over the 18 degree angle that peaks in the center. The screws must penetrate the center of your T-bar and it can be difficult to clamp this connection for this process. Let the self tapping screw do the work and don't apply a lot of pressure. You will find that spinning the self-tapping screws at high speeds may burn up the cutting tip.
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Dome Kits prefers using the 4V (frequency) Icosahedrons geometry to create geodesic structures. Unlike the 3V used by most dome manufactures the 4V has a horizontal flat line (great circle) at the hemisphere. This makes your foundation connection easier using the geodesic triangles. Once your structure is complete you can remove the area you have decided for your doors and windows.
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The 4 frequency (V) uses smaller triangles than the 3V dome structures. This makes a stronger geodesic structure and also makes the components smaller, easier and safer to handle by one person during construction. Looking up at the center of the hemisphere you see the pentagon point of the five sided Icosahedrons pyramid.
Dome Kits answer to low cost housing. The introduction to geodesic dome building. Light gauge steel T-bar (drywall) ceiling grid geodesic frame. Rigid foam insulation, waterproof stucco exterior and your choice of finished interiors. Ideal for a garage, barn, storage shed or small home. The material cost starts at under $1200. These are the smallest do-it-yourself geodesic structures that Dome Kits offers. These geodesic structures were designed to range under 30' in diameter or 900 square feet of floor space.
You will be starting from the bottom on your frame work with the D lettered struts. These bottom 20 struts will be of different material than the rest of the frame.  1 1/2" X 1 1/2" framing angle. Locate the center of your circle and place a stack or nail to hold your tape to measure the radius and location of the D struts. These structures do not require to be built on a level surface and can be built on any surface. As you complete each row of triangles you will notice that the structure will begin to level itself and take shape. The bottom D struts will become flat and straight.
In Dome Kits framing diagram you will notice all the A struts make up the Pentagons. The Icosahedrons geodesic structure uses the same major triangle to create the total geodesic frame. Start from the center of the pentagon where all five A struts meet and follow it down from the A-B-B-A struts to the next corner and pentagon of the major triangle. Now if you travel horizontal across the A-B-B-A struts you will meet the third corner of the major triangle. Bellow this major triangle you have the same triangle turned upside down. You have five major triangles at the top of your Icosahedrons geodesic frame (the icosa cap). Around the middle of your spherical structure you have ten major triangles facing each other. And to complete the Spherical ball shaped structure you would have five major triangles (the Icosa cap) at the bottom facing down. In the major triangles there is what is called the Frequency ( the total number of struts from the pentagon center to pentagon center). Dome Kits uses the 4V (frequency) Icosahedrons A-B-B-A.
This diagram is to represent a 4' x 8' piece of foam or any other sheet material you wish to use. There are five triangles in the Dome Kits 4V geometry. In Dome Kits T-bar geodesic frame we have optimized the 4' T-bar strut to build the 24' geodesic structure.
The diagram is showing one of the ways to optimize your sheet goods. You have five triangle combinations; A-A-C, C-C-C, B-C-D, D-D-E, E-E-E. You can save some time and materials by cutting the triangles to align the equilateral sides. The B-C-D triangle can be turned over (reversed) to optimize fabrication. You can glue the two end pieces together to create another triangle.
The cord lengths are calculated by multiplying the formula X the diameter you wish to build.

Example for the 24' diameter Dome Kits 4V dome.

A - 1.52 (30 struts) _____1.52 X 24' = 36.48 -- 36"-1/2"
B - 1.79 (30 struts) _____1.79 X 24' = 42.96 -- 43"
C - 1.76 (90 struts) _____1.76 X 24' = 42.24 -- 42"-1/4"
D - 1.88 (70 struts) _____1.88 X 24' = 45.12 -- 45"
E - 1.94 (30 struts) _____1.94 X 24' = 46.56 -- 46"-1/2"

Your measurements are calculated in decimals. If you round them off to the nearest 1/4" you should be fine. The 24' diameter was chosen because the longest strut is the E strut with a final length of 46-1/2". Using cross T's with a length of 47-1/4" we could not go much longer. The 30' diameter is ideally optimizes 10' strut material and 4' sheet materials. The 39' diameter optimizes 12' long strut materials. Light gauge steel has always been the superior building material over wood. The Spherical Designs Organization offers many prefabricated light gauge steel spherical structures designed to work with rigid foam insulation for the owner-builder and general building contractor.
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We need some way of checking our 18 degree connections and strut angle during construction. My method for this is to use one of the 4' T's and cut the back side 2' from the ends so it will bend to a total of 18 degrees. Take one of the inside reducer washers and screw it in place over the cut out area on your T to hold it from moving. Once you have screwed your washer in place double check your new template to see if it is holding at 18 degrees. 
Now during construction, once you have screwed the inside strut and connector in place you can clamp your new 18 degree jig to the inside of your struts face to face to hold it in place while you screw your outside reducer washer in place. Once your outside reducer washer is connected your strut should hold itself at your 18 degree angle. It never hurts to have another pair of eye's double checking the construction diagram. This is the fun part of the puzzle. This connection system is very forgiving and the light weight materials make this spherical geodesic structure a great  project to start your geodesic dome building adventures.
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The Drywall T-bar ceiling grid can be purchased at the local drywall and light gauge steel stud contractors supply house. It comes in boxes of 4' cross T's and 12' main T's. This is also your source for 1-1/2" x 1-1/2" wall angle for the bottom foundation D struts, rigid foam insulation, exterior synthetic stucco, screws and tools. Once you know the diameter of the geodesic structure you wish to building and have calculated your strut lengths you can optimize the materials that will work best for your dome structure. These geodesic structures were designed by Dome Kits to range under 30' in diameter or 900 square feet using these products. There are 250 struts in the 4 frequency geodesic structure which 20 of these will be 1-1/2" angle for the foundation row.
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