foamcore on steroids

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RECIPE FOR MANLY FOAMCORE:

-3mm MDF-
-30mm polystyrene foam-
-3mmMDF-

3mm MDF bends pretty well and can be cut with a steel ruler & retractable knife - I make an initial shallow cut, then apply gentle bending pressure and make a few more passes with the knife.

The sandwich doesn't even need glue, as such. You can simply paint the MDF with solvent (turpentine), lay a sheet of polystyrene on the damp surface, and apply weight. The turpentine melts the surface of the foam, and the materials quickly bond.

My plan is to tinker / experiment a bit more with scrap, and if this works out, use it as the framework for some fairly large projects, such as ~75Hz midbass horns (that I can pick up with one hand).

POSSIBLE IMPROVEMENTS AND ALTERNATIVES:

My initial idea for the horns was a ply/foam/ply sandwich with a fibreglass skin (for outdoor use) - but I'm looking for options that are less stinky and less costly.

So far, I'm looking at boat building sites to see how they do. The guy who wrote this 'Seafoam Kayak' instructable has a lot of good ideas that I can steal.

Seafoam Kayak, the Unsinkable Foam Kayak Anyone Can Build, 16 Pounds and Eight Feet of Fun - All

- he used 'whipped' expanding foam to seal gaps and to glue polystyrene to polystyrene. This is probably better and more consistent than my ghetto tech.
- he used slightly thinned polyurethane floor sealer on thin cardboard (!) to make a strong and waterproof inner lining for his kayak. I could apply this same idea to waterproofing horns.
- he used titebond + fabric to skin several projects (several kayaks and a teardrop camper), calling it "poor man's fibreglass" - which has a lot of appeal.

NOTE

I'm hoping I can go one 'better' than the latter two options: upcycle some scrap polystyrene foam by dissolving it in cheap solvent (petrol) to the consistency of paint, and use that rather than a commercial glue or resin. So far, I haven't been able to get it to the right consistency: it wants to form a rubbery jelly - which works OK as a glue, but it certainly doesn't flow like paint.

I'm keen to hear of any tips / tricks / secret sauces.
 
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