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Re: Epoxy

ΕΔΔΥ . <overlordmustafa@...>
 

This technique I'm suggesting is not for molding, it's for placing over an are which has had a repair or even as a repair.

If you're worried microballons offer no strength, glass does.  The power ratio of the planes I've used this one is zero, it's for sailplanes and this method has a MUCH higher weight to strength ratio than using most weaves of glass.  I worry about weight WAY more than any homebuilder.  The trick to making fiberglass light and strong (lighter, it's fairly heavy) is to minimize the epoxy.  If you had an entire wing with a wet layup and added 1 layer of 0.5oz/yd^2 you'd end up with a much smoother wing without adding any epoxy.  It's free strength with virtually no added weight.  Although, this is a tangent. 

I'm just suggesting if someone is worried about sanding through a spot of fiberglass, this is a way of repairing without.  Realistically, if one uses fine sand paper, they will not compromise the structural integrity of the fin.  Sand carefully and there will not be any need for any repairs (and I'd certainly take off the primer).





On Wed, Dec 5, 2018 at 12:49 PM Charlie oneskydog@... [Q-LIST] <Q-LIST@...> wrote:
 

Hi Eddy,


This is a great technique for reducing print through of structural fabric weaves in molded epoxy parts. It works by trapping extra epoxy between the fine weave and the structural plies the stiffness of the glass compared to resin minimizes the surface shrinkage reducing print through.

Our goal on a repair is to scarf in and replace structural layers one for one , same weight same direction, slightly below the surface. Any fairing required should be done with a similar resin chemistry filled with glass micro balloons to reduce the epoxy weight and facilitate easier sanding prior to paint.

Grams count our power to weight ratio is way less than your RC models and our repairs can be bigger. I appreciate your thoughts and methods for model repair. Most of our guidance on repairs goes back to Burt Rutan and his pioneering work on mold less composite structures.

Regards,

Charlie Johnson


On Dec 5, 2018, at 9:42 AM, ΕΔΔΥ . overlordmustafa@... [Q-LIST] <Q-LIST@...> wrote:

I've done many repairs on fibergass, I used to build RC models.
One great method to get a smooth final coat of glass is to get the absolute lightest fiberglass you can get your hands on.

After laying up whichever weight of glass (which most people use is rather a heavy weight, compared to what i'm used to using) you can place a layer of  0.5oz/sq ft  fiberglass as a top coat.  This adds virtually no weight, you don't have to add any epoxy. This 'trick' works significantly.  It's like getting strength at no extra weight.

If you're worried about sanding through the fiberglass you could add a layer of this light cloth.  Apply it differently than thicker cloth.  Brush on the thinnest layer of epoxy onto the fin then place the glass over the wet surface.  Slow cure is better over fast cure for this (I prefer slow cure over anything else).

So, if you're worried about digging though fibergass, this is an easy fix.  When you're done it's amazingly smooth.  You'll still need to sand it to get it perfect, but it's close to perfect.

You might want to even bump up the weights(of glass) a bit.  The lightest glass is so thin you can't move it around very easy when placing it (so be delicate when setting the glass down).  An advantage to using the extremely thin stuff is it goes around corners and bends like nobody's business.

Eddy
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