Notes from Brani about spheres
info from FLG Los Angeles division expert Brandi. she did some work with acrylic (plexiglass) spheres.
Forwarded message ----------
From: Brandi Hugo <firstname.lastname@example.org> Date: Feb 2, 2007 12:46 PM Subject: Re: plexi spheres To: Michael Prados <email@example.com>
sure, no problem. Send on to the list.
Potential problems with vacu forming spheres:
1) the larger domes (over 24" or 30" ish) have a tendency to get these thin spots around the edges which means the area where they stick them back together- essentially the 2 hemi spheres are plexi "welded" back together. around the seam there are thinner spots and on really big spheres there can be these weird little marks (almost square little rivet looking really thin spots) that I think are there depending on the size of the mold they use. Honestly they seem more common on the really large ones, but they have lots of little imperfections. Well, those spots are right on a seam which means it's already weak there to begin with, but that makes it worse and they literally explode if you drop them. Not good.
2) depending on the size of the dome, you need to use cast plexi sheet instead of rolled. Very expensive. I think the cast plexi sphere that had a 3' diameter cost me around 750-1000 dollars with materials and labor. This is colored plexi, not clear, mind you. the sheets are a $150 or higher and you need basically a whole sheet for one of those. Many places have white and clear but they recommend certain thicknesses for certain sizes because of the variation in thickness near the edge. i didn't find that even with the heavier plexi that it was that strong but I also went with the thinnest plexi I could for the lowest weight. the finished sphere didn't weigh much more than 20 lbs, if that, it's hard to tell. it did have a lot of stress on the portion that hung from the ceiling, and that was the thickest part. i could send you a drawing to better understand what I am talking about, if necessary. What I am getting at is that the bigger the sphere, the less material there is at the edges and seams and depending on the size, you may need a different type of acrylic.
3) they aren't totally round, they are pretty round though. they may roll funny, I think that's what they are talking about with the lexan. But in lexan's defense, it's stronger AND usually more UV resistant. Plexi gets very brittle without the sun, and more so with the elements (playa not so nice) but you may end up with a slight ellipse anyway
4) if you are going white or clear I know a few sources to buy pre- formed ones. it will be cheaper. i had to vacu form because I wanted custom colors. If you want to do stress testing, you can buy the hemi spheres relatively cheap from security camera people (even get a scratched one or something) as they use them for the domes to hide cameras. You can get mirror plexi too, but i think it's pretty expensive in the hemi sphere and sphere realm.
So i'll attach a photo of the finished lights so you can see that they aren't totally round but pretty close and if you have any specific questions about the process, I may be able to tell you yes or no, or whatever. I actually worked with the spheres quite a bit- i drilled holes and created a wire harness and little tie wrap deal to hold them all together in order to hang them and light them so I did get up close and personal with several spheres and hemi spheres. I actually have a few 18" hemi spheres laying around that I can photograph if you need. I think the big daddy blue one is 36" diameter and it's less round as it goes up... the other 2 are 24" diameter.
Hope this helps...
--- Michael Prados <firstname.lastname@example.org> wrote: > Hi Brandi, > > that's really useful information. the dome formers said the spheres > wouldn't be "perfect" but I had a hard time getting a really clear > idea what sort of imperfections they would have. > The thinning is > definitely an issue. > > is it ok for me to send your email to the swarm list? > > any other thoughts on how to get strong plastic spheres? > > -mike > > On 2/2/07, Brandi Hugo <email@example.com> > wrote: > > Mike- > > > > this may be redundant info but I have some experience > > working with 3 foot plus plexi spheres and hemi spheres. I actually > > had a group of them fabricated for > > me when I did a lighting design project. The smaller > > ones are a bit better (maybe 18"diameter)but when you > > get into the 3 foot diameter ones, they get REALLY thin in spots and > > shatter really easily. They are also > > pretty expensive as you know. I think the only way you > > can go big like that with plexi or any material which > > will be further weakened by the sun is by using a non > > vacu-formed version. The sun really wreaks havoc on > > plexi and I imagine any extra stress would lead to an > > early demise. They just can't take any stress, weight, > > even a rough touch- they pop really easily. > > > > I have more info, if you need, but from my experience, > > wiring inside of those things is a real bitch and very > > hard to work with. > > > > can't wait to hear more about swarm, i'm excited especially since i > > don't understand any of the GPS stuff... very fascinating. > > > > best of luck!! > > -brando > > >