So for the KEF Uni Q project……..first and at first glance easiest option would be the large 11” Blanca bowls from Ikea….each enclosure comprised of two halves clam shelled. Not expensive and bracing easily added to compensate for the somewhat thin Bamboo construction.
…..but then I see the stainless bowls……available in 11” and 8”…….one of each would be perfect for epoxy casting half hemispheres. I could even do a carbon fiber layup on the 8” outside and then cast it into the 11”……..a 3/4 thick clear cast layer over CF?… might be something to look at, no?
If my math is correct, each half sphere would be 3/4” thick and take just under 1 gallon of resin to cast……not exactly cheap but under $300 for two 11” full spheres all in with the Ikea stainless bowls as molds and some carbon fiber for the inside layup.
I could join each half together with a circle cut and chamfered piece of MDF……a few mills less than the cast circumference and maybe wrap that with a nice piece of brushed aluminum?……..
These would be heavy though…..certainly as non resonant as could be.
If anyone has any other suggestions for a different casting material….feel free to make suggestions. Would some kind of acrylic fortified cement/plaster or such work too?……it would have to be thin enough to cast into half spheres without significant voids though…..filling, sanding and painting would not offset the cost savings over the epoxy. Nice thing about the metal ikea bowls is I can heat them from the outside to be sure to release all of the trapped air.
…..but then I see the stainless bowls……available in 11” and 8”…….one of each would be perfect for epoxy casting half hemispheres. I could even do a carbon fiber layup on the 8” outside and then cast it into the 11”……..a 3/4 thick clear cast layer over CF?… might be something to look at, no?
If my math is correct, each half sphere would be 3/4” thick and take just under 1 gallon of resin to cast……not exactly cheap but under $300 for two 11” full spheres all in with the Ikea stainless bowls as molds and some carbon fiber for the inside layup.
I could join each half together with a circle cut and chamfered piece of MDF……a few mills less than the cast circumference and maybe wrap that with a nice piece of brushed aluminum?……..
These would be heavy though…..certainly as non resonant as could be.
If anyone has any other suggestions for a different casting material….feel free to make suggestions. Would some kind of acrylic fortified cement/plaster or such work too?……it would have to be thin enough to cast into half spheres without significant voids though…..filling, sanding and painting would not offset the cost savings over the epoxy. Nice thing about the metal ikea bowls is I can heat them from the outside to be sure to release all of the trapped air.
You may want to consider a fiberglass layup. Glass mat isn't the sexy composite but its relatively inexpensive and while it would still hold a lot of resin, it would be stronger than solid cast resin. Chopped CF is worth looking into. It produces a nice looking finish when added to epoxy... maybe a bonus? The main point is that added glass or CF will reduce the weight, increase the strength and shouldn't cost much if anything over straight epoxy. A vacuum pump works well for degassing and if you did want to add an outer CF skin, it would be the tool of choice. Good luck, I'm looking forward to seeing how it turns out.
Amory Lovins with the Rocky Mountain Institute was experimenting with CF/epoxy casting years ago and if I remember correctly, one of his test pieces was bowl shaped and it rung like a bell when struck. I mention that because I found it interesting, but has no bearing on your project. I believe he was using very high pressure in the process.
Amory Lovins with the Rocky Mountain Institute was experimenting with CF/epoxy casting years ago and if I remember correctly, one of his test pieces was bowl shaped and it rung like a bell when struck. I mention that because I found it interesting, but has no bearing on your project. I believe he was using very high pressure in the process.
How about . Just use a ball as a form.(Basketball or other inflatable) Cover the whole thing. Cut in half when set. Add inner ring around one to act as flange when rejoining the two halves.
You might like to look at less noxious materials for your initial foray. Maybe paper mache in a layered process?
You might like to look at less noxious materials for your initial foray. Maybe paper mache in a layered process?
I could do a lay up over the 8" bowl to get to near the 11" thickness and then do a mold pour in between the inside of the 11 and the outside layup of the 8......that would likely displace more than half of the epoxy for the pour,......might save a $100 on resin given the cost of glass
I've seen that CF chop on some newer motorcycle bodywork,,,,,,,,,,and i HATE the look of it.
Ringing would be a problem.........
Lol, yeah it would. I think it took considerable effort to achieve that level of stiffness.
The closest I've come to casting is finding something interesting to pour left over epoxy in before it sets up. I do know that polyurethane resin is frequently used and is a bit cheaper than epoxy. It might be worth looking into.
Also, fwiw, many composite supply outfits sell remnants at a discount
The closest I've come to casting is finding something interesting to pour left over epoxy in before it sets up. I do know that polyurethane resin is frequently used and is a bit cheaper than epoxy. It might be worth looking into.
Also, fwiw, many composite supply outfits sell remnants at a discount
Use a cheep high quality balon and cover it with wet plaster stripes a few layers. (leave a small hole open at the bottom)
Then epoxi wet stripes in so many layers you want, and make a hole in the balloon & pull it out.
Fix the small hole and finish of with Plastic pading.
Then epoxi wet stripes in so many layers you want, and make a hole in the balloon & pull it out.
Fix the small hole and finish of with Plastic pading.
Attachments
The easiest way by far to do what you want to do in my experience is a rotomolding technique. Get a globe/sphere that is the diameter you want the outside to be, cut a hole in it and start with polyurethane resin. I've even used balloons with a modified technique. PU resin sets up fast, so it's simply a matter of rotating it randomly in all directions to cover the entire interior, or if you start with a solid sphere just look through the hole and eyeball it.
Then you can move to epoxy resin, which will take much longer to cure and limit the depth you are able to do at one time, and here I would advise rotating every now and then, and then setting it down...ultimately leaving it in one position to cure as actually you don't want a spherical inside due to a harsh resonance at a single frequency. So I usually do them in multiple pours and have a flat spot on the bottom at the end of each pour while also slowly building the thickness. Make a triangelish or squarish inside, up to you.
Coating the outside with epoxy is best done on something that slowly rotates, so you can keep adding coats continually from what drips off and maintain a perfect sphere, but when I started I also hung them from jigs with collection underneath, got a 12 pack and done the same thing by hand until it starts to set up.
As far as something cheaper to occupy space I like to use hydrostone, which is made for casting art pieces. Sets fast, can be cast thin, super smooth and just like stone. You could also just use layers of cementall though, cheaper and more readily available. I always finish with epoxy on the last outside or inside layer just because of the toughness however, and because of how well it takes impact, as well as dyes, pigments and mica powders.
Epoxy is a thermocured polymer and is not very resonant, but the structure itself is resonant, especially a globe, thus stay away from spherical interior.
Also, both marine epoxy and hydrostone set up extremely hard and the compressive strength with full cure is easily over 10,000 lbs per square inch, so the mass and hardness does a very good job of not letting vibrations pass to the outside of the enclosure and excite the air again.
Then you can move to epoxy resin, which will take much longer to cure and limit the depth you are able to do at one time, and here I would advise rotating every now and then, and then setting it down...ultimately leaving it in one position to cure as actually you don't want a spherical inside due to a harsh resonance at a single frequency. So I usually do them in multiple pours and have a flat spot on the bottom at the end of each pour while also slowly building the thickness. Make a triangelish or squarish inside, up to you.
Coating the outside with epoxy is best done on something that slowly rotates, so you can keep adding coats continually from what drips off and maintain a perfect sphere, but when I started I also hung them from jigs with collection underneath, got a 12 pack and done the same thing by hand until it starts to set up.
As far as something cheaper to occupy space I like to use hydrostone, which is made for casting art pieces. Sets fast, can be cast thin, super smooth and just like stone. You could also just use layers of cementall though, cheaper and more readily available. I always finish with epoxy on the last outside or inside layer just because of the toughness however, and because of how well it takes impact, as well as dyes, pigments and mica powders.
Epoxy is a thermocured polymer and is not very resonant, but the structure itself is resonant, especially a globe, thus stay away from spherical interior.
Also, both marine epoxy and hydrostone set up extremely hard and the compressive strength with full cure is easily over 10,000 lbs per square inch, so the mass and hardness does a very good job of not letting vibrations pass to the outside of the enclosure and excite the air again.
Resin Research was brought to market by a surfboard shaper and composites set builder for Hollywood.
They put out some great products. Developing an epoxy system with the good traits of polyester resin and the strength of epoxy was the goal. The toxicity and smell of PE was driving shapers to epoxy but it was slow to set up and cure, usually cured witj a yellowish tint and didn't lend itself to the colorwork often used on surfboards. Its been a huge success water clear, easier sanding and more controllable working/kick times mimicked PE to a large degree. Two additives they applied might be helpful to your project. Additive F, allows a hard cure but aids in effective post cure sanding and X-55 which speeds up fast hardener mixes even more, to allow what is called a Hot Coat when working with PE without have to handle MEK. Awful stuff...
They put out some great products. Developing an epoxy system with the good traits of polyester resin and the strength of epoxy was the goal. The toxicity and smell of PE was driving shapers to epoxy but it was slow to set up and cure, usually cured witj a yellowish tint and didn't lend itself to the colorwork often used on surfboards. Its been a huge success water clear, easier sanding and more controllable working/kick times mimicked PE to a large degree. Two additives they applied might be helpful to your project. Additive F, allows a hard cure but aids in effective post cure sanding and X-55 which speeds up fast hardener mixes even more, to allow what is called a Hot Coat when working with PE without have to handle MEK. Awful stuff...
@mayhem13
Nice project. Some things to bear in mind. If you cover the speaker opening with paper and tap and thump. Would you hear just the paper or a tabla?
There is a way around this which might work for you. Can you find polystyrene balls in the required size? Slice that up in layers and take the middle material out of each layer. The more wall thickness, the better. Reassemble, but add a layer of paper skinned foam core board between each ball layer. Cut some holes in the foam board. Assemble the whole thing using my goo formula and use it as the internal paint and external primer. This can then be glassed for painting or veneered using cold moulding. As a bonus this can be done on the kitchen table and results are consistent and predictable
Nice project. Some things to bear in mind. If you cover the speaker opening with paper and tap and thump. Would you hear just the paper or a tabla?
There is a way around this which might work for you. Can you find polystyrene balls in the required size? Slice that up in layers and take the middle material out of each layer. The more wall thickness, the better. Reassemble, but add a layer of paper skinned foam core board between each ball layer. Cut some holes in the foam board. Assemble the whole thing using my goo formula and use it as the internal paint and external primer. This can then be glassed for painting or veneered using cold moulding. As a bonus this can be done on the kitchen table and results are consistent and predictable