So, I'm going to be building a quarter sized nearodesic polyhedron ("quad")
dome (1 rmax sheet = 8 triangles) for BRC this year.
My foamcore and masking tape prototypes (1:12 and 1:5 scale) have been
going well. I'm learning how to do the tape hinges, and how to miter the
edges with a razor and angled metal guide. I'm thinking that the full size
version will be relatively easy to prepare and construct. My end result is
a 6' high, 12' diameter dome that folds down into a 4' x 4' x 15" high box.
Minimal tape is required as all but one edge of each quad is hinged with
fabric and adhesive. Only the top square, and 4 "corners" need to be fully
taped together.
I'm seeing lots of people commenting on how the BFT (bi-filament tape) is
not really UV resistant, so it flakes off eventually. Also, that it's
barely a semi-permanent solution, even if you do tape hinges instead of
one-time assembly. I've considered many different types of ways to join the
triangles that would last more than one or two times:
- zippers (needed like 400 of them, really really expensive)
- button snaps and straps (would glue on the snaps to the boards, then use
a strap to snap them together; this is not weather proof at all)
- velcro (again, pretty expensive if you use the really good velcro, which
is likely the only way to guarantee structural integrity and
'weatherproof-ness')
- magnets (even using strong ones (N45), embedding them in the edges of the
triangles, they could jsut fall out, and still not weather proof. also $$$)
..and a couple of other ideas. I've learned that putting metal
hooks/rods/bolts (binder clips) through the boards will just rip through it
with a strong enough tug. They could end up just getting loose and boring
out big holes. Using plus-shaped ("+") hooks/rods to fasten some sort of
fabric over the joints are slightly better because they resist being pulled
like a wire cutter through the board, but you would have holes in the board
and water could get in. Also, excessive force would also just make the
holes looser and ruin the boards eventually. But the idea of using some
sort of fabric seems to hold merit.
My main goal is to build something that can easily be packed away, and
assembled multiple time. Realizing that the main principles of a good BM
structure are to seal out rain, dust and light, I think I've come up with a
possible solution, but I'm curious why I can't find anyone who has tried it.
* I'm hoping to get some cautionary tales or some encouragement on using
sport nylon (as opposed to ripstop), and some Super 77 or 80 or 90 spray
adhesive, instead of the traditional tape.*
The cost might be a little more expensive up front (depending on some
factors), but I'm thinking that the nylon will last much longer than just
about any tape and is probably just as strong (if not stronger) than BFT.
>From what I've read, a lot of people end up using some 77 spray anyway
because of the lubricating residue on the boards. I'm curious if it's more
UV resistant (or at least the adhesive would be) and therefore survive the
endless sun bathing better. Also, the concept of cutting fabric into strips
and using spray adhesive as a backing gives the user many more options when
it comes to materials (stronger fabric and/or stronger glue), rather than
just limiting to such a rare find as 6" BFT. Though I'm sure that sport
nylon "tape" is even more rare. You can also make the strips as wide as you
want, so you are not limited there either.
I've built a prototype of a hinged triangle using foamcore, sport nylon and
Super 77, which seems very, very strong. Stronger than masking tape anyway.
I'm thinking that while it's not waterproof out of the box, I could always
spray with some scotchguard, or tape over everything with the foil tape.
Foil tape would also help any concerns on fire-hazard as the adhesive is
quite flammable. I put a hairdrier on it for about 10 mins on high, to see
if excessive heat made the glue loosen, but it did quite well. I'm thinking
the higher temp ratings of 80 or 90 adhesive will help in that area. Maybe
instead of foil tape. I can spray with some sort of coating that will
protect against fire and water at the same time.
For cost comparison, my project would be using about 6 rolls of 60yd tape.
That's about $20 a roll. Plus about 4 rolls of foil tape (for outside only)
at another $20 a roll. I'm thinking that a can of adhesive will last quite
a long time, so I may only need about 3 cans at about $20 a pop. The fabric
is not that expensive (maybe 5 dollars a yard), so I think all in all, I
might come out saving a little cash (if any at all), but ending up with a
much more permanent/reusable solution.
Anyway, what do you all think? I'm going to be purchasing a piece of
polyIso to test. I'm going to make a single "quad" using this nylon and
adhesive, then leaving it up on my roof for a week or two to see how it
handles the weather. It's Santa Monica CA weather so not quite the same,
but should give a good indication as to whether it will survive at all.
Thanks for reading!
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