Geodesic Dome Connector Plates

© Brooke Clarke 2009

Since the 1960s when Bucky Fuller (Wiki) was at San Jose State I've been interested in Geodesic Domes (Wiki).  Back then (no internet) I bought every book related to domes I could find and all of them left me with the question "What is a geodesic dome?".  The Sunnyvale patent office files by class number rather than by patent number like ALL the other patent libraries.   This allows manual searching a given class number.  This is the library serving the semiconductor industry among others.  Anyway, after reading Fuller's patent
2682235 Building construction, Fuller Richard Buckminster, Jun 29, 1954, 52/81.3, D25/13, 403/115, 52/630, 403/56, 403/144, 52/519, 343/872, 52/DIG.100
it's clear that alternate vertices are just above and just blow the surface of a regular surface like a spheroid or ellipsoid.
This is but one example where fundamental information that's in a patent is left out of books.  So for some things the only place where you can get the basic idea is by reading patents.

I read each edition of the "Whole Earth Catalog" (Official web page, Wiki) and the biggest problem was making a dome water tight.  But for use in a garden to keep the wild animals from eating plants that's not an issue.  There are other problems, see the dome Wiki.

This particular page was motivated by my interest in the sheet metal connector plates that are available to make single frequency domes like the StarPlate.

The StarPlate was sold by Strombergs Chickens who hold the patent rights.  It's intended to join five struts (2x2, 2x4, 2x6 lumber) to make a single frequency dome where the strut length is up to nine feet.  Their instruction sheet shows: Carport, Wood Shed, Machinery Shed, Storage Building, Greenhouse, Ice Fishing Hut, Corn Crib, Screened House, Vertical Sided Building, Gazebo, Chicken Coup, Hutch, Basic Framework, Covered Sandbox, Cabana.
Note: This plate is different than the CH5 that has provision to connect to either 5 or 10 struts.  See patent 4384801 below.

The primary strut mounting hole is about 0.406" I.D.  (5/16" bolt)
The primary mounting hole for the axillary struts is about 0.390" I.D. (5/16" bolt")
The nail holes for the auxiliary struts are about 0.165"  (? nail size, maybe #8 screw?)
The central hole is about o.365" I.D.  (5/16" bolt?)  Why is this hole here? Contact me if you know

See my fasteners page for diameters.

The distance between the mounting hole center for any of the primary struts to the center of the center hole is about 2.4".  This dimension would need to be added to both ends of the strut hole-to-hole length to get the center-to-center length that's the same as one side of a triangle face.

The CH5 is different than the StarPlate in that the CH5 has provision to attach 10 two-by boards.  Five are the same as on the StarPlate and the additional five are between the StarPlate five.  The auxiliary boards go between the hub and the center of the strut opposite the the hub (to the strut connecting the struts on either side of the auxiliary board).  The auxiliary board can be connected to the CH5 using either a single bolt or using two nails/screws.  The auxiliary board needs to have it's far end miter cut so that it's end is parallel to the strut.   A single nail can be driven through the strut into  the auxiliary board.   The auxiliary boards could be the vertical boards in a doorway and the regular struts omitted.

This was the plate that came in the kit of 11 plates from Strombergs Chickens!!  It looks like they are now shipping the CH5 instead of the plain plate.

Bill of Materials

25 Struts or 5 struts treated for foundation + 5 longer struts for roof overhang + 15 struts for walls and top plate
50 5/16"  carriage bolts might be 2.5", 3.5", 4.5", 6.5" ,etc. depending on size of strut lumber (2x2, 2x3, 2x4, 2x6).
50 5/16" nuts
50 5/16" washers
It might be better to use Loctite 222 instead of lock washers.
Update;
Stromberg's Chickens now offers kits that include the nuts, bolts and washers for either 2x2 or 2x4 struts.

Description	#	unit	$/unit	Total
2"x4"x10' struts	20	ea	2.66	53.20
2"x4"x10' pressure treated struts	5	ea	6.00	30.00
carriage bolts 5/16x4-1/2" for 2x4 lumber 5/16x2-1/2" for 2X2 lumber	2	box	28.87/25	57.74
5/16" washers	2	box	4.50/25	9.00
5/16" lock washers	2	box	4.50/25	9.00
5/16 Nuts	2	bag	4.23/25	8.46
shade cloth (top & South) (6'x30' roll)	2	rolls	30/roll	60
shade cloth to wood clips	4	bag	4/30	12.00
1" chicken wire (9 side triangles) (3x50 roll, 3x25 roll	2/1	rolls	28 / 17	73.00
tbd door
Total

Single Frequency sizes

The StarPlate literature suggests that nine feet is the maximum strut length.  This may be based on building codes and may assume plywood or other sheeting covers the dome thus subjecting it to snow loads. 
The StarPlate Connection by Norm Lee says they were designed to use either:

Length	Material	Additional Bracing
6'	2x2	none
8'	2x4	none
10'	2x6	eve cable1 or central post

Note 1 - Yurt (Wiki) is the term for a building that uses an eve cable.  That way an arched or peaked roof can be supported without a truss.

There's another limitation on size and that's based on the length of common sizes of lumber and how straight they are.  In my case I want to build a cage for a garden that will keep out Deer, Rabbits, Turkeys, Squirrels, Birds, etc. so there's no snow load and the building weight is very low.  There's no runoff water consideration.  I don't think this would be called a green house, maybe a Garden Cage or better a Garden House.

  SimplyDifferently - Dome Calculator -1V/L1 2/3 Icosahedron Dome calculator. 1V: Single Frequency, L1: there is only one strut length, 2/3 of a circle not a full ball.

This table ignores the connector plate and is theoretical in nature. 
Strut Length is between two adjacent central hub junction points.  The idea is to get some feel for how strut length relates to dome size.

side feet	S	2	3	4	5	6	7	8	9	10	12	14	16	18	20
Lumber		2x2	2x2	2x2	2x2	2x2	2x4	2x4	2x4?	2x6	2x6?	?	?	?	?
triangle ht	h	1.7	2.6	3.5	4.3	5.2	6.1	6.9	7.8	8.7	10.4	12.1	13.9	15.6	17.3
triangle area	A	1.7	3.9	6.9	10.8	15.6	21.2	27.7	35.1	43.3	62.4	84.9	110.9	140.3	173.2
Floor area	B	6.9	15.5	27.5	43.0	61.9	84.3	110.1	139.4	172.0	247.7	337.2	440.4	557.4	688.2

h = Triangle Height =SQRT(3)*S
A =  Triangle Area = 0.5*S*h
B = Floor Area of pentagon = 1.720477*S*S

Note: If the strut length exceeds the size of the covering material then the auxiliary strut will need to be installed.  This is not really a two frequency dome since the shape of each surface is still an equilateral triangle (Wiki).
It can be attached at the plate end using either a bolt and/or nails or screws between the main struts.
At the other end it will need to be cut at an angle so that it can be attached to an adjacent strut using a couple of screws or right angle StrongTie - metal A brackets.
The instruction sheet has the needed cutting angles.

4498800 Junction Plate, Ulrich Sielaff (United steel Products Co.), Feb 12 1985 403/172 ; 403/217; 52/81.3 - CH5 Gazebo Hub Plate

Fig 1 & Fig 2

Fig 5 & Fig 6

4384801 Junction plate, David O. Hamel (East-West Design Group)  May 24, 1983 - the StarPlate

Fig 1 StarPlate

Fig 3 StarPlate with Struts