Fillers for smooth-on products?

[spasticteapot]

I'm hoping to use Smooth-On "Onyx" resin for a pair of speaker enclosures, and would like to use some fillers to make it cheaper, heavier, and stronger. The speaker enclosures are hollow spheres roughly 13" in diameter and with .75" thick walls, and need to be very stiff to minimize cabinet resonance.

I was thinking something along the lines of a combination of chopped PVA or glass fibers and some sort of powdered filler - perhaps one of the smooth-on "Ure-Fil" products? Also, has anyone tried slush-casting large objects?

I'm new to working with resins, and would appreciate your input.

 

[exoray]

There is always a trade off with fillers, they alter the properties of the resin...

Most will make the resin noticeably thicker, thus for a slush or roto-cast it might cause issues...

You should use a slower resin if you use fiberglass, as it needs a full wet out time to work properly, the 3 or so minutes from mix to cure for onxy isn't really ideal for fiberglass... If I was going to use fiberglass with it I would stick to a fine milled fiberglass, and refrigerate the resin it will buy you a few more minutes for the fiberglass to wet out before it kicks...

If you want it more 'solid' you can add a ceramic dust filler,it will make it more like stone but on the flip side you risk making it more brittle to impact and stress...

Also .75" is a pretty tough shell on it's own without any fillers...

 

[spasticteapot]

If I was going to use fiberglass with it I would stick to a fine milled fiberglass, and refrigerate the resin it will buy you a few more minutes for the fiberglass to wet out before it kicks...

I'm using the Onyx over a slower resin due to the tremendous hardness it offers - in terms of strength, it's not far off from concrete. I'm hoping to just mixed some chopped fibers into the mixture and pour it in as opposed to a traditional lay-up.

The refrigeration is a good tip - I'll have to try it. However, Onyx is a really, really quick resin either way. I've been told I can just mix up the mixture a pint at a time and pour them in sequentially by the local Smooth-On distribuitor; apparently, so long as I finish the whole thing within half an hour or so, it should fuse together into a solid whole. That said, if you have conflicting evidence, please feel free to share.

 

[exoray]

I'm hoping to just mixed some chopped fibers into the mixture and pour it in as opposed to a traditional lay-up..

You won't be able to add much fiberglass if you want to pour, no where near the ratio of a hand layup... You will go from water like resin to thick syrup real quick and with a 2.5 minute pot life, it won't have time to self level as you increase the thickness of it by adding fiberglass... You can certainly add some but it's going to be a give and take...

The 2.5 minutes they spec for the pot life is only an estimate, if it's above say 75° you can start to lower that time... You will easily waste half that time mixing the two parts properly and adding the fiberglass...

May I suggest you do several test before you jump right into doing the final, it can be done but as I said it's going to be a give and take...

 

[spasticteapot]

That's very much interesting. According to my estimates, I need about three gallons of resin for my speakers. I was hoping to get by with one two-gallon kit, but it seems that I'll either need to use a slower resin or use thinner cabinet walls. Or spend another $90 on resin.

 

[Eaglewood]

I'm hoping to use Smooth-On "Onyx" resin for a pair of speaker enclosures, and would like to use some fillers to make it cheaper, heavier, and stronger. The speaker enclosures are hollow spheres roughly 13" in diameter and with .75" thick walls, and need to be very stiff to minimize cabinet resonance.

I was thinking something along the lines of a combination of chopped PVA or glass fibers and some sort of powdered filler - perhaps one of the smooth-on "Ure-Fil" products? Also, has anyone tried slush-casting large objects?

I'm new to working with resins, and would appreciate your input.

I work very closely with my Smooth-on guy and the Onyx--great stuff. He has a guy that use powdered glass strand and mixes it with the Black Onyx to make pistol grips. He sells the crap out of them and they are the strongest things--light too!!

 

[spasticteapot]

I work very closely with my Smooth-on guy and the Onyx--great stuff. He has a guy that use powdered glass strand and mixes it with the Black Onyx to make pistol grips. He sells the crap out of them and they are the strongest things--light too!!

Could you ask him what it is? I'm afraid I'm a bit lost at the moment.

 

[exoray]

Could you ask him what it is? I'm afraid I'm a bit lost at the moment.

Powederd glass strand = milled fiberglass same as I suggested, it's fiberglass strands that has been mechanically powdered in a hammer mill...

 

[Eaglewood]

Powederd glass strand = milled fiberglass same as I suggested, it's fiberglass strands that has been mechanically powdered in a hammer mill...

you got it!! Thanks Exo

 

[ToddsCostumes]

I'm hoping to use Smooth-On "Onyx" resin for a pair of speaker enclosures, and would like to use some fillers to make it cheaper, heavier, and stronger.

Why not try some test mixes with anything and everything you can find? Mix up a few ounces and throw in some filler, pour it out to let it harden and see what you get. Most of the fillers mentioned will reduce the mass, and I think you want to increase the mass. The shape you mention should be pretty strong, so you could probably give up a little strength, especially with a 3/4" wall thickness. Some ideas that come to mind are dried sand, plaster, and metal powder. Since you're going to slush it on the inside, it doesn't have to be pretty (and it won't be!!!)

-Todd