[JohnR]

I'm interested in making a curved shape. It's 3D so bendy plywood won't work. I was thinking about using small pieces of sheet material, and gluing a netting of some kind at the joins, and then using some sort of filling material to fill in the cracks. Then sand the whole thing.

Would anyone be able to suggest what type of thing would be best to use for the filler? My first thought was plaster, but I'd be worried it might be brittle.

[Chromisdesigns]

You could make a female mold from just about anything -- foam, wood, plaster, give it a fine finish, then lay up laminate over it.  Carbon fiber / epoxy would probably work well for speaker parts, as it is very stiff.  If you want wood, you could laminate over a curved mold with veneer strips, the way cold-molded boat hulls are made.

Or you could stack laminate your favorite wood, cutting pieces to approximate the curve you want, then work it down to the final surface with a hand grinder and sanders.

If you post more details about what you want to make, I and others may be able to be more specific.

[JohnR]

Good question. Maybe something like this:

http://www.instructables.com/id/Low-cost-Spherical-Speaker-Array/

Although not using that method.

[mcgsxr]

Not sure what aesthetic you are chasing, but for complex, compound structures in the car audio world, it is fleece overlaid with fiberglass all the way.

Could you use a material like chicken wire to shape the intial structure, then cover in fleece, and then fiberglass?  In the end the chicken wire comes out, and you have a sandable, paintable base of fiberglass.

I would bet that member Hebrew Hammer could offer a wealth of ideas, given the posts he has with his unique shapes and finishes etc.

Good luck!

[JohnR]

Thanks Mark - what do you mean by "fleece"?

[WGH]

A mold may be the best way to achieve the shape you want. I would stack laminate the rough shape out of a soft wood like aspen, basswood, or even pine then plane and belt sand the block to the shape you want. A grid pattern with templates would guarantee a fair curve.

Once your form is perfect, lay on glass fabric using either polyester resin or epoxy to make a shell that you can use to cast the speaker front.



Unfortunately I don't have a good idea what to fill the fiberglass shell with, concrete comes to mind but the project becomes very labor intensive after that idea.

If the form sounds like a good idea then take a look at the West System web site, they sell the epoxy I use. The site has a wealth of knowledge along with customers projects and the Epoxyworks Magazine that has tips and technical data that may give you some ideas. I use epoxy because it is the only structural glue, with West epoxy you can build or fix almost anything.
http://www.westsystem.com/ss/

Stack laminated wood or plywood would make a good speaker surface too. The speaker holes can be routed and counter sunk while the surfaces are flat and then the front is curved using templates as a guide. I use the excellent sandpaper made by Klingspor for roughing out hard and dense woods like mesquite when I make a natural edge table. I start with a 36 or 40 grit Alumina Zirconia (very hard, sharp grain) sanding belt and go up to 400 grit when finally done. Alumina Zirconia is excellent for grinding of stainless steel, spring steel, titanium and other hard steels and for dimensioning of wood. Alumina Zirconia may also be used for heavy stock removal of plastic, rubber, glass and stone or concrete products.



Those blue belts will make short work of any sanding or shaping job, they stay sharp forever and when sanding wood never get dull. Klingspor Abrasives are made in Germany so they may be available in Australia too.

Wayne
 

[mcgsxr]

JohnR, by fleece I just mean regular polyester fleece like used in blankets or jackets etc.

Here is a link to a build that outlines the steps, though it is focused on a subwoofer box, you could likely rig up any shape you want, to get it going.

http://www.explorerforum.com/fiberglass/fiberglassing.htm

[MaxCast]

Are you looking for a full sphere, semi-sphere or longer curved panel?

[Bob in St. Louis]

John, I did a plywood frame with a wire mesh, then wrapped it in fiberglass cloth and resin. I used those speakers for a few years and was very happy with them.
I can find pictures and maybe a thread if you'd like.

Bob

[doug s.]

john, are you wanting a sphere, or just a long curved panel?  have you considered sonotubes?

some day, when i have the room for the finished product, i am going to build a line source, and i will use a sonotube for the cabinet.  these are wery strong, even w/o reinforcement, and they're easy to reinforce...

doug s.

[madisonears]

Carve a model of the shape you want, using wax, which is very easy to shape and smooth, and it's cheap.  Coat the wax model with plaster or sink it right into a bath of wet plaster.  Melt the wax or remove the wax model from it.  You now have a plaster negative mold of your finished shape.  Fill that with polyurethane, which can be shaped and machined, and is reasonably inert acoustically, but rather expensive.

Peace,
Tom E