I am building a TF Folke Wulf 190D. The plan suggests the use of milled fibreglass mixed with 30 minute epoxy to provide a strong connection between the fuse and stab.
The local hobby store is presently out of milled fibreglass.

Is the use of milled fibreglass required to strengthen the connection?
The hobby shop suggested the use of micro balloons - does this increase the strength?
I have never seen milled fibreglass. Will shredding fibreglass and mixing with epoxy produce the same result?

Neil

Milled glass is cheap, that's for sure. It's $7.85/lb at CST. A pound is a lot of FG fluff.
http://www.cstsales.com/high_strength_fillers.html
The strength of FG comes from the tensile strength of the fibers. Chopping the fibers up kills that. It is a nice light weight filler, though. I doubt that there would be a big difference between the glass and the micoballoons. The main idea is to build the lightest possible fillet, since it's so far back on the airframe. Fillets won't provide a huge amount of strength, but some, certainly. Now I'm using West System 410 filler in their slow dry epoxy and getting the lightest, easiest to sand fillets I've ever had. I'd call it a toss-up. Use what you are happy with.

njjd,

Microballoons will not add strength to the epoxy mix; they simply make it thicker to act as a filler. Milled glass really adds the strength. I've made my own milled fiber mix by shredding some glass cloth and it worked ok. You'll need more than you think you will. When you add the fibers to the resin they really shrink down so the volume that you have when you're creating your pile of milled fibers disappears rather quickly. I couldn't get it as fine as the milled fibers I was later able to buy but like I said it worked ok.

I'm with js3 on this. Although the fibers are "chopped up", they provide a matrix that the epoxy interbonds with on a microscopic level, and gives the epoxy a much greater shear strength. Microballoons are microscopic glass spheres, and are used to expand the volume of epoxy,, lighten it, thicken it, and make it more easily sandable, but they add almost no strength to the mix. Think of them as tiny bubbles, and mixed with epoxy, make a "froth" that is great for making filleted joints and seams. Using either one will shorten the working time of whatever epoxy you're using, also.

When working with either the microballoons or the milled fiberglass, be careful not to inhale ANY of either. They will blow around like dust, and getting them in your lungs can lead to pulmonary edema and asbestosis-like symptoms.

If I want lite, I just use microballoons; for strength I use milled fibreglass. Sometimes I use both. It depends. But I ALWAYS use my trusty 3M respirator mask. Either product can do nasty stuff to your lungs. One of the fellows down the road from me has a tiny pump imbedded in his chest to pump out the fluid that builds up in his lungs. He never smoked, but he breathed in powder and fibreglass, on the job, 'cause he didn't use his mask. Bummer[]

R.C.

Ditto on the mask thing. I was starting to play around with fiberglassing and using styrofoam in my model builds and came to the conclusion that it was really a bad idea. I have pretty much switched to building with balsa only and even try to use non toxic glues when possible.

You can get cotton flox at aircraft spruce and specialties cheap. Its the best. I use it on models and full scale. don't use microballoons if you are looking for strong joints. It is weak.

Have you guys noticed the 'kick' time when using either microballoons or glass is a LOT shorter?

Jerry

Don't use them with 5 minute epoxy, either one of them

I use 5 min epoxy with milled 'glass all the time, no problems. The more you use, up to about 1/2 glass, 1/2 epoxy, the shorter the working time gets. I only do small jobs that I know I can get done in a couple of minutes, like cowl blocks. Never had a problem with strength, either; BUT, you got to be ready and work fast, or it will set in a heartbeat and you're only half through.

Yea, thats why I don't do it, it sets fast. Well, I guess thinking back, I have done it, but Man, it goes quick.

Sorta makes you feel like a one-armed Chinaman on an ARF assembly line, don't it?