Looking for...

[seawasp]

Hollow but not inflatable (i.e., rigid) spheres, or better yet 12" - 24" sections of such rigid spheres, with the diameter of the sphere being about 4' (48").

Edit: For use in experiments with a longer focal-length microphone that needs a parabolic (except not parabolic) dish. Needs to be very cheap (i.e., I doubt the tank-ends mentioned by one poster would work out -- they're probably many dollars each.) -- I'm thinking of a few bucks a pop or less.

Comments

[shana.livejournal.com]

This is a little small but: http://www.plasteelcorp.com/foamshapes/smoothfoam_styrofoam/10073-1.html

[seawasp]

Too small and too thick. I'm thinking of something like the plastic balls you see in the ball pits except 4 feet across, or a small section of such a ball (like a miniature snow saucer)

[argonel.livejournal.com]

Do you have any material preferences? Plastic, Aluminum, steel? And for sections are you looking for shallow dish shaped pieces or pie pieces?

I'm guessing that you want something that looks like the roof panels of a mini observatory.

[seawasp]

I'm looking for shallow dish-shaped pieces. Material is not an issue, low cost and a reasonably smooth (though doesn't have to be mirror-smooth) finish is.

[seawasp]

Addition: curvature is important. Spherical (or, I suppose, parabolic, but that would almost certainly be custom, and expensive) curvature for about 48" or so (24" is too small, 96" too large probably)

[argonel.livejournal.com]

I don't have a specific source for you, but I would recommend talking to a tank fabricator. Most tanks have hemispherical endcaps that are welded to to a central tube section. For example Arrow tank http://www.arrowtank.com/ is very local to me, but not local at all for you. Depending on your specific requirements you may even be able to make a deal for a scrap piece that fails testing.

Alternately you might be able to get the endcap off a decertified propane tank for cheap.

[argonel.livejournal.com]

Another source for hemispheres, http://www.amsind.com/ . Armadillo Aerospace was using them as a supplier for spun aluminum hemispheres to be welded together into rocket fuel tanks.

[alex swavely (from livejournal.com)]

You could get them made from plastic via vacuum thermoforming fairly inexpensively

[brownkitty.livejournal.com]

Does it need to be a complete and perfect sphere, or would spherical connectors from a playland maze be adequate for your needs?

[seawasp]

As I said, sphere sections; like a satellite dish, sorta. Though if I have a whole sphere, I can cut the sections out.

[kpreid.livejournal.com]

Especially large outdoor lamp globes?

[mouser.livejournal.com]

What do you need it for so we can guess better?

[seawasp]

A parabolic-except-it's-not dish for a microphone. With a long Focal Length.

That's REALLY cheap.

[mouser.livejournal.com]

Oh.

Get a wok. They're almost the right shape.

[kgbooklog.livejournal.com]

Sounds like you want a used satellite dish, though consumer ones are probably too small. Any telecoms going out of business near you?

[seawasp]

Satellite dishes have the wrong radius of curvature; they're designed for a much closer focal point. Unless they're BIG satellite dishes, which is larger than our target size.

[kengr]

Ask local metal fabricators about getting spun metal "bowls". Odds are that if they can't do it themselves, they can point you at someone who can.

[kengr]

Oops. missed the price bit.

Used dogloos?

Or just get the right sized weather balloon, rig a frame to hold it and apply fiberglass on the top half?

[dragoness-e.livejournal.com]

Beach balls of the semi-rigid plastic variety?

[argonel.livejournal.com]

Check your local home improvement big-box store. They may have vacu-formed plastic thingies designed to cover skylights or act as mini greenhouses. If so those are usually about a 3 foot hemisphere. Alternately you might be able to jury rig a devize with a sheet of plastic, a support frame and a threaded rod through the middle of the sheet. On a down side you would end up with a cone shaped cavity instead of a hemisphere or parabola, but on the positive side it would give you an adjustable focal length.

[brooksmoses]

Paper-mache formed on a large balloon?