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Old Aug 21, 2014, 06:28 AM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
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Question
Epoxy filler substitutes?

I'm looking for suggestions for "kitchen cabinet" type substitutes for epoxy fillers. just getting into composite building and have nothing on hand. Yes, I will be ordering some proper fillers with my next composites order, but looking to wrap up the current project, a scratchbuilt mini-DLG. I'm gluing the wing onto the wing saddle. The fit is imperfect so I need to mix up something that has strength and will fill small gaps but ideally not too heavy. I can chop up some glass &/or carbon fibers and mix that in, but hoping to find something else that will add lightness while bulking up the mix? I have read of using baking soda, or balsa dust, and was considering fine-sanded blue foam dust. Suggestions or comments?

And while I'm here.....for "proper" fillers, I was going to order microballoons, cabosil, choppped glass. Will that cover the needs of the novice composites hack?

Thanks as always for the help!

- Jim
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Old Aug 21, 2014, 03:40 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Jim,
I don't know, but the balsa dust is worth a try.
If you have a commercial fibreglass manufacturer in your home town, take a jar there and ask them to sell you a small quantity of "Q" cells or microballoons.
That is where I get mine. I actually buy a box of it at a time now. (1kg maybe?). That lasts me a couple of years.

Second question:
To your list I would add some flocked cotton/ colloidal silica mix. It is sold by Wests Systems, Epiglass and others. The Wests is marketed as 403, but I think in the US it is sold as 404, which is very confusing. I would love to know why manufacturers do such things to us consumers!
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Old Aug 21, 2014, 03:59 PM
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Blackrat's Avatar
Jeffreys Bay South Africa
Joined May 2006
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i guess any powder could work ... if its just going to be used as a filler

baby powder .... ?

i got about 20kgs of corian powder ... havnt tried it yet, but dont see why i cant use it as a filler
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Old Aug 21, 2014, 05:16 PM
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Jim.Thompson's Avatar
Bellingen NSW Australia
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Quote:
Originally Posted by Blackrat View Post
i guess any powder could work ... if its just going to be used as a filler
baby powder .... ?
...........................
Talc can be used; I use it for plugs but not for flying parts. This is a DLG application, so weight is a major factor, the various ground rock type fillers are too heavy for this.
I buy industrial talc; baby powder without the stinking perfume and at a fraction of the cost.
Is the ground Corian just the ATH? (Aluminium Trihydrate) Or is it ground up ATH with the binding polyester resin?
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Old Aug 21, 2014, 05:37 PM
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JimZinVT's Avatar
United States, VT, Castleton
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Hi Jim! Yes, I've read of using talc too. Weight is not huge issue here, this is a trial run of composite building for me, first time. She's already a bit overweight, so a few more grams won't be a worry. Lighter is certainly better but primarily it needs to hold up to the discus launch. If the fit were perfect I'd Just epoxy it down and be done, but there are some small gaps to bridge. I may mix up a couple sample blobs tonight and see whats what.

20kg of corian.....that's heavier than my dog.
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Old Aug 21, 2014, 08:09 PM
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San Francisco & Santa Cruz
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For the moment, I would suggest wood dust (sawdust) but maybe hardwood not balsa. Foam dust is only going to make it weaker. In general, you can add either lightness or strength, but not both at the same time.

For the future, I would suggest milled glass rather than chopped glass. Milled glass is much shorter fibers that mix well into epoxy. For high strength gap filling, I use cabosil together with milled glass. My chopped glass I think is 1/4" fibers, and it doesn't mix in well at all. I should probably give it away...
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Old Aug 21, 2014, 09:31 PM
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New Zealand, Tasman, Richmond
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Adding talc to resin works as a filler but it greatly reduces the strength and durability in my experience - this may not be a priority though. Wests High Density filler is better, and now I've discovered ATH I like this even more. But these are heavy. For the lightest solution I'd be going for micro-balloons....
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Old Aug 22, 2014, 12:44 AM
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Cornflour works too, nice and light and you've probably got some already in the cupboard
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Old Aug 22, 2014, 09:03 AM
Canada
Joined Jun 2009
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A small can of automotive body filler comes in handy in the shop and will do the trick nicely to get a good fit. Has worked for me.

Paul
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Old Aug 24, 2014, 08:13 PM
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United States, VT, Castleton
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I ended up using chopped carbon fiber....I snipped about 6" (15cm) of 12k carbon tow to ~1/16" (1.5mm) size and mixed it with 5g of epoxy. It made a nice goopy mess that filled the small gaps. It took less than 2g to do the job.

I decided strength was more important here than lightness, so I didn't add any of the "light" options.

Thanks for all the suggestions.
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Old Aug 31, 2014, 10:54 AM
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Zenmaniac's Avatar
near Madison, WI
Joined Jan 2009
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Quote:
Originally Posted by Blackrat View Post
i guess any powder could work ... if its just going to be used as a filler
Gun powder?

-= Dave
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Old Aug 31, 2014, 02:25 PM
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United States, AL, Daphne
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Quote:
Originally Posted by JimZinVT View Post
I ended up using chopped carbon fiber....I snipped about 6" (15cm) of 12k carbon tow to ~1/16" (1.5mm) size and mixed it with 5g of epoxy.
I might do something similar, did you just use scissors to chop the carbon into 1/16" bits?

Trey
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Old Aug 31, 2014, 03:09 PM
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JimZinVT's Avatar
United States, VT, Castleton
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Yes,that's what I did. It takes longer than you'd hope. Sharp scissors help. I didn't use my scissors with the "kevlar grind" but that would probably help.

It worked well....the joint seems really strong.
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Old Sep 01, 2014, 10:44 PM
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Calgary, AB, Canada
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Talc is used in putty's & primers & fillers for increased sandability because its one of the softest minerals (1 on a scale of 1-10, quartz = 7, diamond = 10) & it's sheet like minerology. Think of it as something close to chalk.
http://en.wikipedia.org/wiki/Mohs_sc...neral_hardness

Also, its really not all that light, density ranges from 2.6-2.8 g/cc. Compare that with microballoons at 0.2-0.6 g/cc. So kind of misses on 2 points, structural & weight.

Microballoons make for very sandable fillets in cured resins & bulk up the volume due to their nature. For more strength add milled fibers which are pretty common as low as in 1/32" length. For increased viscosity, add cabosil. These are the primary recipe ingredients used in different proportions that will get you through the bulk of modeling & composites IMO.
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Old Sep 01, 2014, 11:00 PM
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JimZinVT's Avatar
United States, VT, Castleton
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Thanks PTX. Those were the ones I was planning on buying the next time I put a composites order in. Nice to have someone confirm my choices.
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