ARCHITECTURE: Geodesic Models Summary.

From: IN%"[email protected]" "List for the discussion of Buckminster Fulle
r'
s works" 28-MAR-1992 17:54:03.04
To: Howard Lawrence <[email protected]>
CC:
Subj: Tensegrity and octetruss models (Summary)

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Date: Fri, 27 Mar 1992 18:27:00 GMT
From: Mitch Amiano <[email protected]>
Subject: Tensegrity and octetruss models (Summary)
Sender: List for the discussion of Buckminster Fuller's works
<[email protected]>
To: Howard Lawrence <[email protected]>
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<[email protected]>
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I recieved some good information, thought it might help someone else, so I'm
posting this summary.
My model is comming along nicely. Just buying the parts right now, but it looks
like
it will come together without too much trouble.

Ideas: (paraphrased)

From: [email protected] (Peggy L Richards)
Read _An Introduction to Tensegrity_ by Anthony Pugh,
LOC: TA658.2 P85x, copyright 1976, University of California Press,
ISDN: 0-520-02996-8 (cloth/hard) or 0-520-03055-9 (paper), 121pp.

For a strut member: 3/4 inch diameter wooden dowel, cut to 9 inch lengths,

To fasten tension members to compression members:
"...18-gauge wire brads (those nails with virtually no head), about an
inch to
1.5 inches long and blunt the points. Warning: Use of steel nails,
pins,
etc. can be dangerous. Pound two nails into each strut end, with a wide
gap between them and at least .5 inches protruding from the wood:
_________________________________
/^\
/ -------o
STRUT (yeah, right) \ -------o two brads, repeat for other end
\ /
_______________________________\/

As tension members: 2 inch #14, or 1&1/2 inch #12 rubber bands hung over
one
of the brads.

A note: "Most of the above was summarized from Mr. Pugh's book..."

From: [email protected]
Company which "makes little plastic components for building various sorts of
models."
Plastruct, ..."located in the City of Industry...California."
"Any good hobby or architectural supply shop in your area should have a
catalog."

Another company based in England which owns the designs Plastruct struts are
made from. He can dig up the names if someone is interested.

A good resource book: "Thomas Register of American Manufacturers",
"...which can be found in many large libraries.

From: [email protected] (Jim Flanagan)
For compression members: "...buy thousands of bamboo skewers..."

Tension members: Rubber bands

To fasten:
"...chop off the pointy
bits, and bind two (or more, depending on the tension in the model)
together with rubber bands thus:

==x=============================x==

then take another rubber band insert it between the two sticks at one
end, then with half a turn drag it down to the other end and hook it
in there. One completed strut. With practice one person can make a good
deal of these in an evening. A hint for keeping the structure together
while building is to use another band to keep a connection firm
(somtimes
a connection will slip. Spectacular explosions attest to the amount of
tension is held in one of these structures...).

~~
//
==x=============================x=x=
//
//
//
~~

To increase tension: twist the rubber bands an odd number of revolutions.
( Why an odd number, Jim ? )

From: me :-)
While considering this, I came be some of my own solutions.

Resources: Check out a good boating supply shop. They make use of a number
of tensile materials and fasteners.

Tension members: Boating supply shops carry in bulk what might cost you
$$$ to get pre-cut: rope, cables, and that elastic cloth cordage (like
the kind used in the Tensegritoy). The elastic cord cost about $13 for
a 50 foot roll.

Tough Tension members: Nylon coated steel cable, 3/32 inch, with crimpable
aluminum cable sleeves. Use the sleeves to make loops in the cable ends.
Cable can be accurately measured by looping around two nails set in a
block of wood and pulled tight. Sleeves can be crimped on one at a time.
The nylon coating makes it less likely to have wire splinters, and
makes for a neater finish.

Taking up slack: Tiny turnbuckles. expensive at >50 cents a pop.
Jim Flanagan's idea to increase the tension of the rubber bands by
twisting
them will work here, too. You just won't be able to twist up very much.
Many forms of strain relief hardware can also be used to give springiness
to inflexible cables.

Compression members: Aluminum or brass tubing, 3/8 inch diameter. Aluminum
costs about $1 a foot, while brass is about twice as expensive.
Neither is hard to cut, given a midget pipe cutter, about $5.

Fastening members together: A hollow tube may be plugged with a variety of
screw anchors, both metal and plastic. Then a small bolt or screw stock
can be securely mounted. Some washers are all thats needed to complete
the connection if you chose to use bolts. For screw stock, you also
need nuts, and can use round-ended cromed nuts for a finer finishing.
For both, cable or rope loops can simply be looped on. Make sure the
loop is smaller than the washer, or it might slip.

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