1st Try with West Epoxy

So, filleting my first fins with West 105/205 (1 pump each) and the addition of the 406 colloidal silica (2TBSP) to achieve "peanut butter" consistency. Seems to spread fine, but there are small particles of the silica that look like dots in the mix...as if they weren't thoroughly mixed. Pic is attached. Is there something else I should be doing, or is this typical?

My recommendation would be to use 407 instead. Never had a problem with it. Never experienced a bonding failure with it. Always produced a smooth, usually glossy finish and was relatively easy to sand when necessary.

The longer you mix it, the fewer particles you will have but I have never been able to totally get rid of those either and I have used the same exact combination on more than one rocket. Somebody else might shed some light on this but it is my thought that at this point your just in for some serious sanding to smooth these out now.

I actually sanded quite a bit and then added a very thin layer of 5 min loctite epoxy that is very smooth when it cures and it filled in some of the imperfections.

Recently I crashed my 3" Wildman and broke a fin off. While repairing it I accidently used far more Coloidal Silica than I wanted and something kinda cool happened: the opposite of what I expected. It did'nt make the mixture even more rough it actually made the best fillet I've ever made. So, maybe it's a simple solution - we are not using enough of the Silica? I will say the mixture was very much like thick peanut butter and perhaps my other attempts were more like runny peanut butter.

I have experienced the same results. My rule of thumb when using 406 filler: make it twice as thick (as you think you need) and mix it twice as long (as you think you need).

The more filler you add the weaker and more brittle the fillet or joint will be. I stopped using colloidal silica and micro balloons and switched to milled glass fiber. It is similar but, it has a irregular particles in it and no hollow spheres or air pockets. https://en.wikipedia.org/wiki/Colloidal_silica

I also use Pro Set which is made by the same people who make West Systems. It works better for gluing fiberglass or dis-similar materials together.
In some applications you actually need some flex to glue joints.


JD

Golfpro62 said:

The longer you mix it, the fewer particles you will have but I have never been able to totally get rid of those either and I have used the same exact combination on more than one rocket. Somebody else might shed some light on this but it is my thought that at this point your just in for some serious sanding to smooth these out now.

I actually sanded quite a bit and then added a very thin layer of 5 min loctite epoxy that is very smooth when it cures and it filled in some of the imperfections.

Recently I crashed my 3" Wildman and broke a fin off. While repairing it I accidently used far more Coloidal Silica than I wanted and something kinda cool happened: the opposite of what I expected. It did'nt make the mixture even more rough it actually made the best fillet I've ever made. So, maybe it's a simple solution - we are not using enough of the Silica? I will say the mixture was very much like thick peanut butter and perhaps my other attempts were more like runny peanut butter.

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Yes, I guess I assumed since he was worried about how they looked visually that he was talking about external (cosmetic/aerodynamic) fillets. For internal fillets I use a structural epoxy (my favorite is T-88 from System Three) and a mix of milled and 1/4" chopped fiberglass.

JDcluster said:

The more filler you add the weaker and more brittle the fillet or joint will be. I stopped using colloidal silica and micro balloons and switched to milled glass fiber. It is similar but, it has a irregular particles in it and no hollow spheres or air pockets. https://en.wikipedia.org/wiki/Colloidal_silica

I also use Pro Set which is made by the same people who make West Systems. It works better for gluing fiberglass or dis-similar materials together.
In some applications you actually need some flex to glue joints.


JD

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jpummil said:

So, filleting my first fins with West 105/205 (1 pump each) and the addition of the 406 colloidal silica (2TBSP) to achieve "peanut butter" consistency. Seems to spread fine, but there are small particles of the silica that look like dots in the mix...as if they weren't thoroughly mixed. Pic is attached. Is there something else I should be doing, or is this typical?

Click to expand...

It is common - when I am taking my time I will sift the colloidal silica before adding it to the epoxy. This mitigates the clumping.

jpummil said:

Is there something else I should be doing ... ?

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I use my cordless drill with a "stirrer" which is a 6 inch length of steel rod, about the thickness of a coathanger. Anything like it will do. Run the drill fast and keep the rod against the side of the cup with the cup tilted sideways, and let a thin layer of epoxy run between the rod and the side. As the boundary layer on the rod gets pulled against the side of the cup, any particles that can't make the "cut" either get bounced out (and worn down) or mashed up (sheared) and mixed. It usually takes me about three minutes to mix a single "pump" of the West this way with colloidal silica. Excellent results. It will do any consistency with the same results, from salad dressing to peanut butter.

And if you are looking for a way to mix non-silicated epoxy without bubble inclusion, this method works as well and takes about one minute.

If the rod is smooth enough, I clamp onto the cured epoxy much later with the rod in the drill and it pops right off with the drill at full speed. I have been using the same rod for over a year now.

Great tips (and reassurance) all!

Yes, these were external fillets...and despite the odd look of the mixture, they came out great! I expect that by following some of this advice, next time will be even better and less stressful :wink:

You can also try 410 Micro Lite. I personally like Phenolic Micro Bubs. FWIW

I use 406 and of course there are some small white spots in the mix.
So far I've had great success with it. For cosmetics I go over the fillets with 220 paper and add a finish with Icing. Sand them down with 220 and then 500!
Slick as Goose Poop!


Eric

Eric1 said:

add a finish with Icing. Eric

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"Icing"?:confused2: