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Old 11th February 2012, 09:35 PM   #261
John L is offline John L  United States
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Sure thing: the more people discuss this, the more others can learn to apply.

And this video, while on a smaller scale, does a great job in showing how to mix plaster to the correct consistency. I learned some nice things from watching it.

Perfect Plaster
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Old 11th February 2012, 11:10 PM   #262
Squeak is offline Squeak  Denmark
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With all the grief the diffuser is causing you, why not just buy four of the nice plastic ones available? I know it's not as DIY, but wouldn't it be nice to get it over with?
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Old 11th February 2012, 11:20 PM   #263
John L is offline John L  United States
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Quote:
Originally Posted by Squeak View Post
With all the grief the diffuser is causing you, why not just buy four of the nice plastic ones available? I know it's not as DIY, but wouldn't it be nice to get it over with?
Which nice plastic ones? You got me there.
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Old 12th February 2012, 02:13 AM   #264
John L is offline John L  United States
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Incidentally I found some interesting articles on resins and which I can use. These three stood out.

Which Resin is Right For Me?

Casting Resins Into Molds

Casting Imitation Wood
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Old 12th February 2012, 02:44 AM   #265
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SubThread split off Near Space -- The Next Frontier

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Old 12th February 2012, 11:19 AM   #266
mightym is offline mightym  United States
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John, interesting video you linked to the plaster mixing. Looks like you've got it covered! Pun intended...

With the other information you posted Re: casting imitation wood, I wonder why you would want to cast plaster at all, just make a rubber mold from your plug, and cast it in wood filled resin. There are also alternative choices of wood flour other than Pecan hull, Boat builders use pine and maple flour as fillers when gluing with epoxy resins. Since the resin casting is also stainable, it would seem to me the better choice over a plaster mold. I worked for a gent who made concrete yard ornaments many years ago in college, his molds were made from a silicone type of rubber that was then encased in a multi-part plaster casing for support while the concrete cured.

Good luck.

John

Last edited by mightym; 12th February 2012 at 11:30 AM. Reason: added content
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Old 12th February 2012, 11:55 AM   #267
Squeak is offline Squeak  Denmark
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Quote:
Originally Posted by John L View Post
Which nice plastic ones? You got me there.
I was only able to come up with EU sellers, but here you go:

Diffusorkegel - Lautsprecher Selbstbau by blue planet acoustic

Click the image to open in full size.

Click the image to open in full size.

Metal:

Click the image to open in full size.

An example of use:

Click the image to open in full size.
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Old 12th February 2012, 01:56 PM   #268
Carlp is offline Carlp  United States
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Quote:
Originally Posted by John L View Post
Incidentally I found some interesting articles on resins and which I can use. These three stood out.

Which Resin is Right For Me?

Casting Resins Into Molds

Casting Imitation Wood
Wow, John, that's helpful info! Thanks for posting.
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Old 12th February 2012, 03:24 PM   #269
John L is offline John L  United States
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Quote:
Originally Posted by Squeak View Post
I was only able to come up with EU sellers, but here you go:

Diffusorkegel - Lautsprecher Selbstbau by blue planet acoustic
The only problem here is that the diameter is just 129mm, which comes out to a hair over 5". That wouldn't ever begin to cover the project. It would be something like staring at a full sized person with a tiny head on top. I need at least 13.5"/343mm.

The shape is great, but it would have to be blown up considerably.

I did a search on Google, for possibly another larger product, but no luck. I typed in several possibilities, but again no luck. Unless someone can come up with one that is at least one foot in diameter, I'll have to go with what I already have.

Last edited by John L; 12th February 2012 at 03:26 PM.
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Old 12th February 2012, 04:41 PM   #270
John L is offline John L  United States
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Quote:
Originally Posted by mightym View Post
John, interesting video you linked to the plaster mixing. Looks like you've got it covered! Pun intended...

With the other information you posted Re: casting imitation wood, I wonder why you would want to cast plaster at all, just make a rubber mold from your plug, and cast it in wood filled resin. There are also alternative choices of wood flour other than Pecan hull, Boat builders use pine and maple flour as fillers when gluing with epoxy resins. Since the resin casting is also stainable, it would seem to me the better choice over a plaster mold. I worked for a gent who made concrete yard ornaments many years ago in college, his molds were made from a silicone type of rubber that was then encased in a multi-part plaster casing for support while the concrete cured.

Good luck.

John
Perhaps something is getting lost in translation.

Quote:
Originally Posted by mightym
casting imitation wood, I wonder why you would want to cast plaster at all, just make a rubber mold from your plug, and cast it in wood filled resin.
Actually I'm not considering casting plaster. I was planning to use the plaster as only the mold. The actual diffraction lens would be out of resin.

I am now considering a silicon mold first up, now that you mention it, and if that doesn't work, then using the fall-back of plaster. By pouring silicon first, the clay parts will not be destroyed.

I haven't looked up price here, but isn't silicone a bit expensive? I would have to use a large frame, and make the wooden supports, shown in the previous page, much closer to the clay. Because as I have it I would wind up needing an awful lot of silicone.

I'm really open to suggestion. This step is definitely the most crucial one in the entire project.

Quote:
Originally Posted by mightym
I worked for a gent who made concrete yard ornaments many years ago in college, his molds were made from a silicone type of rubber that was then encased in a multi-part plaster casing for support while the concrete cured.
Now that I think about this more, you make a good point, and open other possibilities for me. I like this idea.

Here is what I am thinking I might do.

1. apply a thin layer of silicone around the blank clay piece. It would have to be applied with a brush, because gravity would try to get it to pool at the bottom of the mold, leaving the other end of the lens too thin.

If the first silicone application will fuse to additional ones, I could build up the thickness of the silicone outer portion by adding to the original. Then I could just let it all cure.

2. pour the remaining open space inside the wooden mold frame with plaster to fill in the rest of the mold. That would offer the needed support for the silicone portion of the mold. That would complete the 'negative'.

3. turn the completed portion of the mold over and use that for pouring the resin into. Then the silicone could be removed and a releaser applied before putting the silicone back. That way the two could be separated easily, after a resin mold has been applied and cured.



Now this brings up a choice of two possibilities. If I only use a one piece cast(the outer curve of the lens), without an inner part of the cast, I will have to pour in the resin, and take a brush and spread the resin around, all over the mold, constantly building up the thickness of the resin until it starts to harden.

And I believe I can use more than one coat too. Correct me if I am wrong. Then once the coat is thick enough, remove it from the silicone part of the mold.

And too, I suppose I could also make a silicone mold of the inner side of the clay blank if I have to, making a complete mold for pouring the resin, by using one pour. If I don't have to do this, I'd rather go with the first option, and just brush on the resin to obtain the thickness I need, if I can get away with it. I'd probably go through several cheap brushes in the process.

I saw this applied on a Youtube video last night in which a duplicate bronze plaque was made by first using a special bronze power mixed resin, which was hand brushed over the entire mold. After that part started to set, another batch of resin was poured over it.

Here is the video: Resin Casting: Cold Cast Bronze Process

And lastly, I could do as the people in this video did: just fill the entire volume within the outer mold with a cheaper filler. That way I would have a solid half to glue to the other solid half.

The only two obstacles to this approach would be the 1. cost of the filler , and 2. the weight of the lens. If I used a very light weigh additive for a filler, I could make the resin go further, and it would help lighten the overall weight.

I'd just have to make certain that none of the lightweight filler made it to the outer edges of the lens. I will have to drill holes into the lens in order to add supports for holding the lens above the speaker, and have enough strength to use washers and nuts to tighten down the assembly. If I had the lightweight filler there, it could make the final tightening less secure because the washers and nits wouldn't be able to work on a solid foundation.

Am I making sense here to everyone?
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