Wood Compound Angle Connection
Dome Kits no connector connection. We don't believe there is anything prettier made of wood than the spherical geodesic structure connected with the compound angles cut on the ends. This connection method shows all the geometric angles and done correctly is
truly a piece of art.
There are different types of geodesic geometry and different frequencies. They all have the basic concept to finding the angles at the node points (connection of the struts). From the center of the sphere (ball) a line is projected through the outside surface. This gives you the radial and axial angles. Where these intersections take place depends on the geodesic geometry and the frequency of the intersections.
This is definitely the most labor intensive and difficult connection system to cut with all the proper angles. Most all geodesic dome kit manufactures will not attempt this connection
method and instead try to sell you a $5000 steel connectors. Dome Kits uses the 4
frequency Icosahedrons geodesic geometry. This only adds to the complexity of the manufacturing process but simplifies the construction method.
There are a few inherent advantages to this connection system over the steel bolt together hub connectors. You are not drilling big holes down the center of your wood strut. With the compound angles cut to properly fit under compression, as the wood swells and contracts it does not move or change the connection angle as the steel bolted hubs. 3" wood screws have great holding power without undermining the integrity of your wood strut.
The geodesic geometry Dome Kits uses has been changed from the original 4
frequency Icosahedrons geometry and any other geodesic dome manufactures use. The changes were made to simplify the manufacturing and construction methods. There are 5 different cord lengths and different angles on each end of the 5 struts.
This web page is created to share a generic connection for an all wood connection system. There are
three saws I have used over the past 30 years that can cut a 60 degree angle and a 9 degree angle at the same time.
The radial arm saw, a modified miter saw with the stops removed and
drilled out and Sears sells a 60 degree worm drive skill saw. This is a special order
item and cost near $300. This is a must if your a dome building contractor.
All the wood geodesic dome kits manufactured by Dome Kits are cut with a radial arm saw. All the different angles are cut within one-tenth of one degree. You can not be this accurate with a skill saw. A bolt together steel hub system may move in and out fifteen degrees or more. If your geodesic structure gets to far out of round at the lower levels it can become
difficult and even impossible to complete.
All these compound angles were cut with my 60 degree Sears worm-drive
circular hand saw. You don't need a tape measure or level to put together your geodesic frame together. If your connections are not as perfect as the pre-cut kits from Dome Kits your exterior plywood may not fit as
accurately. This also holds true with the drywall on the inside of your geodesic structure.
In the hemisphere of the 4V geodesic structure there will be 6 pentagon connections and all the others will be hexagon connections. There will be 5 deferent triangles if you use the construction method that Dome Kits uses. If your connections come together
accurately you can cut 4 to 5 pieces of plywood at a time. This is one of the
advantages of using the 4V Icosahedrons. Your plywood and drywall can be mass produced and easier to
handle by one person.
The pentagon connection angles are 72 degrees and 9 degrees. The hexagon angles are 60 degrees and 9 degrees. You will be cutting 54 degrees off each side of the pentagon strut. REMEMBER! The A lettered strut is one directional. The one end is the pentagon and the other is a hexagon. I mark my A struts with an arrow (A>) so I know what end is the 54 degree pentagon and the other will be a 60 degree hexagon cut.
The lower levels of your geodesic dome structure carry all the weight of the structure. This adds a great deal of pressure pushing outward on your connections. Adding a 18" or 24" steel strap on
the outside of your horizontal struts is one off the best way to enhance
the structural integrity of your connection and geodesic structure. All hardware stores offer Simpson Strong -Tie galvanized engineered strapping.
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.
This is the Simpson Stronge-tie Gazebo connector #GT6Z. If you don't like the way your connection looks or fits together this connector can be a nice compliment to the rigidity of your connection and
structure. The plywood is the most important structural part to any structure not just geodesic structures. The building code requires nailing around the outside edges no more than 6" apart. In many areas you have nailing inspections for your plywood and drywall.
On the geodesic structures you are relying on end nailing or perimeter nailing. OSB and particleboard have poor shear quality and should NEVER be used on geodesic dome
structures. Multi layer plywood is your best choice for a lasting structurally
strong geodesic wood structure. If you are building a structure to live in you will want to use 2X6 material. This will give you the
minimum insulation R-value of R-19 using fiberglass bat material. The roof area of geodesic structures are not vented. Dome Kits
recommends you use spray on foam or rigid foam insulation. This gives you a moisture barrier and triple the R-value.