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Old 3rd January 2008, 01:12 AM   #41
OzMikeH is offline OzMikeH  Australia
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No wuckers.
It's the least I could do in thanks for such a useful thread. I've been terrified of using veneer until now.

Would be wise to use some wire mesh for reinforcement. Perhaps cement might be more durable than plaster.
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Old 3rd January 2008, 01:24 AM   #42
John L is offline John L  United States
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Quote:
Originally posted by OzMikeH
No wuckers.
It's the least I could do in thanks for such a useful thread. I've been terrified of using veneer until now.

Would be wise to use some wire mesh for reinforcement. Perhaps cement might be more durable than plaster.
Tell me more about this. Please. I am serious about this, but am completely new to the process.

If I use a sand method, I will need to do it in two parts: an upper and lower, and then adhere them together.

Please explain completely and tell me what type of plaster I will need and the steps. I did some checking on plaster and there are different types.

PS: is that the same thing as "No wucking forries"?
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Old 3rd January 2008, 02:21 AM   #43
OzMikeH is offline OzMikeH  Australia
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Yep, an abbreviation of an already cryptic figure of speech.

I've just made a model with my kid using plaster of paris. That is what gave me the idea.

You only need the hole in the ground, make the top flat. you can round the edge of the top over with a scraper while the plaster is still "green"

You carve the hole out of damp sand, I suggest making something like a giant spade drill bit out of thin plywood. If you get the right sort of sand with the right moisture content it will hold the shape well. You'll need a small trowel to scoop the "drilled" sand away. maybe a vacuum cleaner with a small hose.

If you do this in a flower pot of appropriate size the edges of the pot will be the sides and self-centre the "drill"

mix up too much plaster of paris, fill the flower pot moulds to overflowing and scrape the top off like they do with beer in belgium.
Let cure, wont take very long. then shape the top edge.
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Old 3rd January 2008, 02:39 AM   #44
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This is ten times easier (and more fun) than my method!
Nice idea Mike.
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Old 3rd January 2008, 02:47 AM   #45
John L is offline John L  United States
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Here is something else we must keep in mind. Let's go back to the picture for a moment. And remember there will be no top compression horn to be erected above the horn, as in the picture

Click the image to open in full size.

Remember, I will need to drill six holes into the dispersion horn so as to affix six supporting rods above the driver and tweater combination. Will I be able to do any precision drilling, and then tighten down the screws/bolts without cracking or breaking anything?
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Old 3rd January 2008, 03:26 AM   #46
OzMikeH is offline OzMikeH  Australia
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1/3rd of a cubic foot of plaster will be rather heavy.

I'd let them rest on three legs made of flat material. No need to drill or machine it, the legs will form a cradle.
Maybe some 3mm brushed aluminium plate with various sized holes for that Lost In Space, flying saucer look.

If it was me I'd file the holes into hexagons.
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Old 3rd January 2008, 03:51 AM   #47
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Quote:
Originally posted by John L
Here is something else we must keep in mind. Let's go back to the picture for a moment. And remember there will be no top compression horn to be erected above the horn, as in the picture

Click the image to open in full size.

Remember, I will need to drill six holes into the dispersion horn so as to affix six supporting rods above the driver and tweater combination. Will I be able to do any precision drilling, and then tighten down the screws/bolts without cracking or breaking anything?
Random thoughts:

Cast the rods right into the diffusor.

Cast some coupling nuts into the diffusor, then screw the rods into those.

Cast in metal or plastic tubes, and secure the rods into them afterwords with epoxy. Make the tubes big enough to allow you to align the rods on installation, in case the tubes are a bit off vertical.

Plaster alone would be heavy and not too strong, especially if the rods must attach to a thin rim. You might find that some variation on hypertufa (a lightweight concrete made of Portland cement, peat and perlite, generally used for casting garden pots and such - Google it for more info than you could ever want) would be lighter and stronger. I don't know how easy it would be to get a smooth enough surface on it, it might need a skim coat of plaster to serve as a base for finishing.

Casting resin would be another option, but you'd need a good mold for that.

See if a local potter can spin your diffusors on a pottery wheel. A fired glazed finish could make these into works of art. Probably cost a bit, but might be worth it. Is there a college with an art department near by?

Bill
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Old 3rd January 2008, 04:24 AM   #48
John L is offline John L  United States
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I'm not quite understanding what you mean by making hexagon holes. Let me get some pictures so we can take a closer look at things.

Click the image to open in full size.

Here is a cross section of the Venus.

Click the image to open in full size.

In my project, the top of the horn really doesn't need to be rounded as with this Duevel, since the high compression horn on top will not be mounted there. I could even have the top completely flat. However, I don't think it would look all that pleasing since there are already too many straight lines and it needs some breaking up of this to give it a more pleasing set of lines. So, I think a slight rise/rounded top would look best, but certainly nothing like is shown here on the commercial products.

But if you look at the supporting rods in the cut-away, they are drilled into the material (wood/plaster/clay/etc) and affixed/glued/screwed to it so it will be a permanent fixture. Then is is secured to the top of the cabinet, around the cabinet's corners, next to the driver. I would think that six round rods, perhaps aluminium, would be best to work for this arrangement. That way I could use a screw or bolt to secure it to the cabinet too. And if I could not find a hollow aluminium rod, I can always use a tap and create my own threadings there for a long screw.

But a flat material on top would totally defeat the asthetics AND radiating ability of the horn effect. In fact a flat surface would not have a horn effect at all. It really needs to have a curved horn effect, or it will not work properly.

I am worried that the plaster may weigh a good bit. That is why it would have to be very secure.

Another thing: is there anything that can be used in the plaster mix that would make the mold lighter. Something such as Vermiculite, which is used in granulated form in potting soils? The vermiculite is lightweight, porous, light in color, and absorbs water. If it was mixed within the plaster cement, it would act as an aggregate to lessen the weight.
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Old 3rd January 2008, 04:56 AM   #49
John L is offline John L  United States
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Quote:
Originally posted by lousymusician

See if a local potter can spin your diffusors on a pottery wheel. A fired glazed finish could make these into works of art. Probably cost a bit, but might be worth it. Is there a college with an art department near by?

Bill [/B]
I hate to sound like "Everyman", but I have some decent experience on the potter's wheel. When I was in the service I used to go with a friend to the Fort Jackson main craft shop. There I met a Tom Turner. I believe his first name was Tom. He had an MFA in ceramics and ran the ceramics section as a way to work out his time in service. He had been drafted right out of college into the army.

Through him I learned how to properly wedge the clay, center it on the wheel and throw a pretty good cylinder. I even made a large umbrella stand out of three cylinders. If you have never thrown clay and pulled up a cylinder, you have no idea how hard it is. The key is in centering the clay on the moving wheel. If it is off center, the cylinder will not go up in a stable wall.

I have made a lot of vases and pots, many which have been gifted and broken, and my Mother has a few. I even have some left. Here is one, a hanging basket that I still have around the house.

Click the image to open in full size.

Anyway, because of this I fell in love with ceramics, and seriously thought about entering graduate school and major specialize in ceramics. But my BA was in history and I would have had to practically start all over. I gave up, and became an anthropologist instead.

Anyway, doing this in ceramics was my first thought, but I realized the logistical problems doing this. I have not been on a wheel in over thirty years, so I would be very rusty. And furthermore, the community craft shop manager told me that I would have to take a cource first to prove that I could be trusted on the equipment. It's part of the standardized rules.

I may still fall back on this avenue, because it really would produce a nice piece of work.

Now there are problems doing it with clay. first off, you would have to order special clay, because the normal clay used in pottery shops and crafts centers are usually a combination of Georgia Kaolin, at least some form of fire or ball clay, perhaps some porcelain, and last but not least "Grog". Grog is a rough material that is added to the premix, and it adds roughness and body to the clay. It is not all that good for making shapes that are smooth and silky. It's also rough on the fingers, and will eat up your fingers until you have developed enough callouses.

Anyway, I thought about it and considered it as potentially a last resort, because the next class at the craft center was on some Kooky thing that did not interest me at all. But I will think about it if I cannot come up with something more desirable.

But yes, I have seriously considered a ceramic dispersion horn.
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Old 3rd January 2008, 06:22 AM   #50
OzMikeH is offline OzMikeH  Australia
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plates would be oriented like spokes, producing less obstruction than round legs.

not exactly what I mean but you get the general orientation and holes are what I was talking about.

If you have access to a potter's wheel that could be used to shape the sand mould.
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