I have an old trunk in my backyard
The trunk is 18 ft height and the diameter at the top is 2.8 ft

Step 1:

I think I am obsessed with the geometry of truncated Icosahedron
(These and all others Platonics and Archimedians geometric solids)
but for this project, I will built a regular geodesic sphere

On the top  of a tree trunk in my backyard

before I do the real one, i decided it is better to make a prototype.  (I know all implications that occur when you scale a model or make with different materials :)

Dimensions for the real sphere:
To build a sphere with a radius of 4.25 feet requires:
70 Struts 2.63 feet each bend angle 18o
60 Struts 2.32 feet each bend angle 16o
52 Bolts, 52 Nuts, & 104 Washers

Originally I was at Safeway and bought 2 boxes of 100 straws for $3.99
Then I calculated the size of the straws based on the maximum possible length of the straw (5.5 inches)

Dimension for the model
The maximum possible size of the straw was 5.5 inches:
70 Struts 5.5 inches each
60 Struts 4.8 inches each
52 Bolts, 52 Nuts
model trunk diameter 5.99 inches
model trunk height 37 inches

Step 2:

The first step was to cut 70 straws (Struts) with 5.5 inches each and cut 60 straws (Struts) with 4.8 inches each. I made a small device to guarantee all cuts were the same without needing to measure one by one. I used a heavy trunk and a side of a table as a reference to cut.  I measured one time only, the heavy trunk did not move, so, all subsequent cuts are the same. (this technique guarantees the quality of the production process)

Step 3:

I bent and made holes in both sides of all 130 straws

Step 4:

I assembled the first pentagon with the short straws (4.8”) inside and the long straws (5.5”) outside.

Step 5:

I then assembled 11 other pentagons (total 12 pentagons) all the same.

Step 6:

The first assembly step was, in each vertices of the pentagon, I attached another vertices of another pentagon

Step 7:

I then attached the sides of the all pentagons

Step 8:

By repeating this operation again and you will have two half spheres ready to be connected.

Step 9:

Connect the 2 vertices of each pentagon with the 2 other vertices of  the other 2 pentagons 

I made it at Techshop

Step 10:

after that I got a piece of a tree trunk (diameter 5.99 inches and 37 inches in length)

Step 11:

I tied the geodesic sphere to the trunk

To mock the final product of this Intructable

Step 12:

Once the prototype showed satisfactory structure and stability, I decided to go for the real project

Step 13: End of SubInstructables - BUILDING a SPHERICAL MODEL FOR STUDY

Step 14:

To make a quick test on the real size, I was at home depot and bought 5 pieces of 10 foot ¾ EMT Conduit 

Step 15:

After that I made 3 cuts in each. Two cuts with 2.63 feet (2” 7’ ½) and one with 2.32. (2” 3’ ¾) the result was 4 struts, 2 with 2.63 feet and 2 with 2.32 feet

Step 16:

Filed the ends

Step 17:

then bent all ends

Step 18:

then, I punctured to make a hole in each end

Step 19:

I made a 25/64 diameter hole in each end

Step 20:

After that I bent all ends with a angle of 18 degrees for the long ones and 16 degrees for the short ones

Step 21:

with all struts, bolts, washers and nuts ready, I started the assembly of one pentagon to check the overall process

Step 22:

Looks good

The next step was to buy 28 pieces of  10 foot ¾ EMT Conduit and make 11 more pentagons a total of 12 pentagons
About 320 feet of conduit ¾ 10’ (1408 Lbs ~ 700 kg)

As you can see, I made it at Techshop

Step 23:

The only step I feel deserves a comment in this part of the process was when I took all the remaining pieces,
with the support of the Dream Consultant of Techshop to help me find a better way  to quickly band the pieces to the correct angle 

Step 24:

Then I assembled the 2 half spheres

(see the video Instructable - Geodesic Sphere)

Step 25:

and put the two halves together to make my geodesic sphere

(see the video Instructable - Geodesic Sphere)

Step 26:

Then I drove home with my sphere safely tied to the bed of my truck

Step 27:

After 1 day I revised all plans including the detailed process to assemble the Geodesic Sphere in the top of the tree trunk, after all that, I discovered that the tree trunk did not reside on my property  :((

it was a bitter discovery,

well, anyway, never give up

any suggestions as to what I can do with my sphere?
be nice :)



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Very good idea, I will decide in 2 or 3 weeks and do it :)
thanks for the suggestion :)

It's plenty large enough to turn into a small chicken coup, though access might be a bit of an issue. could also add thin plexi or clear heavy-duty plastic and make a sort of temporary greenhouse.

Personally, I'd suspend a light-weight medium (like bark from the stump) in the center and grow air plants inside (epiphyte). The sphere is open and airy and almost fantastical, so "floating" plants hanging out in there seems quite fitting to me.

Dig up the root structure of the trunk and move it onto your property.......

I have 2 other trunk in my property suitable to do it but...
the enchantment was broken
that sphere was born for that trunk
no other trunk will feet

she need find a new path in her life
may be a room or a chicken house

the sphere now need a new destiny



Is the trunk's property owner friendly? Worth a shot to talk to 'em.

Is property of CalTrans, probably I am out of the game ...ahahah...
but I am waiting suggestion (nice ones) about what to do with this sphere :)

They'll never know! Looks like the land is not commonly accessed at all.