How to build an acrylic dome

[MadProps]

Hey! I am building props for a production of Beauty and the Beast, and have figured out the magical rose problem, using electromagnets, but am having trouble finding an economical method of building the large bell jar that it sits in. It needs to be plastic/acrylic since it's around 70 kids, and clear (obviously) with a diameter of around 10-12" and about 18" high. Any ideas? Possibly casting it from a mold, but have never done this, and not sure where to start.

[Footer]

A vacuum form machine would be the way to go. Do you have access to one or someone that does?

[FatherMurphy]

Trying to vacuform something one piece 18" tall and 12" in diameter would be a bit of a challenge, I think...

Might be easier to think of it as a two-part problem, a hemisphere and a cylinder. You might have a glue line to deal with, but if the match it close enough, it shouldn't be very noticeable. If you have a sign shop in the area, they might be good people to check with, since they deal with a lot of strange plastics and shapes.

I'm not thinking of anything off the top of my head that's that size/shape/clear that you could simply buy and use part of, perhaps someone else will think of something. Candy machines do keep coming to mind, though.

[rochem]

For our production last year, we just basically used an off-the-shelf part from something that we paid only a couple dollars for. All it needs to be is a clear dome thing right, nothing special about it? I wasn't involved in getting it and so couldn't tell you where it came from, but I'll try to ask my TD next time I see him.

[Van]

Vaccu-forming "acrylic" material can be a PITA ! A few years ago, when working for a local Scenic House. I was asked to create a "Space Helmet" for a cucumber....... Yes a cucumber. It was for the touring company that does Veggie Tales. I was daunted. This thing had to be 20" tall, about 18"in diameter at the bottom and then tapering to a rounded point. If you've ever seen and of the veggie tales videos with them in space you'll know what I was emulating.
Anyway, I did some research and eventually found a Teflon based plastic called PTFE. You've probably seen it used as a slider on something, it's usually white and slippery. They make a sheet version of it that is clear and one demonstration of it's properties that I observed was a mask with a long pointy nose that was about 24" long and only about 1/2" in diameter. For those of you familiar with Vaccu-forming you know that this shape would be practically impossible to pull from a standard piece of plastic.
Ok long story short, too late, you could easily pull a shape like that from ptfe, you can try acrylic, but everything I've every pulled from Acrylic, if it's more of a curve than say a skylight shape, tended to fail miserably.

[MadProps]

I don't have access to a vacu-form machine, so I was thinking of creating the two seperate pieces idea-a cylinder and a hemisphere. They only problems in this would be a)finding the pieces and b)attaching them together seamlessly. I wish I could make it as one piece, but with the size, it just doesn't seem feasible within my budget.

[venuetech]

a search for "acrylic dome display cover"
turned up this unit for $229. I dont think you could tool up for that cost plus your time costs.
this is their largest unit so there may be one sized closer to your requirments.
The company also has a note that states this product may take up to two weeks to produce and ship.

15" dia
24" high

Display Accessories, Display Cases, Curio Cases, Glass Domes And Shop Display Cabinets By Fine Home Displays

apparently it is called a Cloche or English Belljar, often used to protect plants from frost.
suggested search "glass cloche" these would have a knob on top that would give it a bit more character.

[erichart]

I've used those bell jars before... it was for a university production, so it couldn't have cost as much as $229. They're sometimes used to display butterflies. Try floral stores or any of the craft chain stores (Michael's, Hobby Lobby, etc.)
If you do decide to fabricate it out of two parts, I don't think you can get a seamless weld unless you laser-weld it. If you can get the two parts to fit together snugly, and the edges are super-smooth (by flame-polishing with a blowtorch), you can get an almost invisible seam by gluing the two halves together. Try a sample to see how much an almost-invisible seam will bother you from the audience seating.

[Thefoxygranpa]

Don't forget to check out your local thrift stores. I've seen those dome displays in both acyrilic and glass at the local goodwill. Sometimes clocks are put into them.

[davedietlein]

I just bought a 20 inch dome on-line for $145.00. I am curious what you paid for your electromagnetics. I am now looking for inexpensive ones.