Right, and if he had a solid block of Styrofoam (glued up or one solid block) he could do half at a time, that way the wire could be “out” of the mold when heating up, then rotated down to dish out one side of the sphere, do this twice and there are your halves… I think that the wire would have to be something like a spring wire that would hold “some” shape when heated, after it was bent, but not too thick or the juice needed to heat it would dim a neighborhood… maybe 3/32” or so. You could stiffen the straight sections by running them through some thin diameter pipe with some bushings from wood that would take the heat for a few minutes when getting the wire hot and act as bearings. I would speculate that you would have to go slow and do several passes to keep the wire from deforming as it cuts……
Since the wire would only be to cut the hemisphere, he could lay up the styro block in layers with pre cut out circles that would minimize the cutting the wire would need to do, kind of a layered circle hemisphere, the wire just trims off the edges of each layer….
I found one place that made them out of fiberglass for $1,685 each. Like anything else, when the size gets over about 16", everyone wants them for gold exchange. I have found all types of plastic, fiberglass, metal, etc., domes, spheres and hemispheres, but everything is still in the hundreds, by the time you add shipping. Anything that is inexpensive, is either too small or not a true sphere/hemisphere. I have found nothing local to Tyler.
I'm going to say, that at this point, I will call it a second fail. Well, a second result that did not fit my requirements, or something like that.
Just some food for thought. I think you’re onto it being concerned about maintaining consistent pressure.
Apply the first layers with primer instead of glue? Primer has excellent sanding characteristics when dry. Might want to use a fast dry alcohol based primer to avoid having to baby sit the ball pressure.
Also, I wonder if you could connect the ball to a small compressor and set the output pressure low enough to maintain constant sphere pressure regardless of temp changes from ambient or evaporative cooling. As each successive layer is applied and the sphere becomes more rigid the pressure can be increased. Then apply a thin layer of a quality material to protect the outside.
Just a wag but each layer has to be completely dry before another is added since it’s only drying through the outer surface. Any moisture left in previous layers will weaken them and make it more susceptible to warping. Big sphere might need 3/8” or more wall thickness too.
As you say, this thread has lots of different ideas so just adding mine.
Instead of air, filling the ball with water might work as it has less thermal expansion. An cheap and easy way is to use an old tubular bicycle pump. Remove the top cap, fill the tube with water, insert plunger, push, repeat. When I was a kid and our pump wore out we chopped off the hose fitting and made one heck of a squirt gun like that. Wondering aloud if the weight of the water would deform it too much?
Just hoping to re-encourage “Old-Lumens” because I like to see people succeed!
The method with the paper requires too much time.
I made my sphere of polyurethane foam. Directly sprayed over the ball. It does not stick to the ball.
After cutting it on two parts,I applied one layer aluminum foil and painted it with a white ceiling paint.
OL, have you thought of using something like this?:
This stuff hardens within 30 minutes and can becomes solid after 1 hour, it can be sanded afterwards. After getting the mold done, use paper mache method to fabricate the actual sphere. or leave it as is?
I think if you can apply an outer layer of this foam one side first, it can harden before the ball changes size? The foam has to be the one with least volume expansion.
I know, bigger is better for you…I made my first sphere out of these dust covers. The largest you can get is a 22” diameter and they’re made out of polystyrene, so they are not incredibly durable. You could buy one for about $40 and use it for a paper mache mold or buy 2 and you’re ready to drill and paint.
I wish they were larger, but if 22” is large enough, it’s hard to beat.
!!
I am looking at 26" mirror domes and I also am talking to a local foam insulation guy, to see if he would spray the ball with his sprayer. I will have to go visit his shop to find out. The mirror domes look good. I am waiting on a reply to see how high they are. If they are 13", well, they should be a perfect hemisphere and they too have flanges on them, so putting them together would be easy. Made of Acrylic though. Pretty brittle stuff and hard to cut. Have to hot cut, so maybe the insulation guy will have a good idea.
Man, that's Awesome. Looks like the outside of a Geode or an Asteroid!
I have something coming, to make a sphere out of. It shipped in two pieces, hopefully today, so sometime next week, I can have another day of cussing and scratching my b ... head.
