[Flying Scotsman]

I'm finishing up the cowling, building up various areas (around the inlets, around the oil door, etc.) to fair them in and make them match and all, using West mixed with microballoons and sanding to a smooth finish. I'm having trouble feathering the very edges of the epoxy, though, and always seem to end up with a very slight "step-off" from the epoxy to the glass cowling. I'm sure my technique is not correct, I'm not a composites expert . I've searched the threads, and I see that some people advocate Rage Gold body filler for small areas...while others seem to indicate that it *shouldn't* be used because of adhesion problems?

So...is it okay to use, does it work well for solving this "problem", etc.? Help!

TIA...

Steve

 

[whittfic]

Can't comment on Rage filler but you should be able to get the epoxy to feather in without too much trouble. Preparing the surface to be filled properly is important as many problems can be caused by poor adhesion.

Cannot be sure exactly what is going on in your case but from what you describe it sounds like the edge of the filler is chipping off leaving the 'step' you describe? If this is the case the filler probably isn't bonding properly, possibly due to the underlying surface not being scuffed and cleaned sufficiently.

The area to be filled needs to be sanded back or roughened to the point where it looks quite dull with a surface texture that looks not unlike fine sandpaper. I commonly use 120 -to 300 grit sandpaper to achieve this. All you are trying to do is removed any surface contaminants and glossy surface, giving the filler something to 'grab' on to. Don't worry about any scratches left in the surface by the sanding process, they will be taken care of by the filler.

When done, vacuum or wipe the dust off with a clean dry rag. Do not wipe it with any solvents and do not wipe your hand over the freshly sanded surface. Even the oils from your skin can be enough to contaminate the surface and affect the bonding.

Apply the filler, let cure and sand/fair to shape. Hint: you will find it easier to sand the epoxy/micro filler to shape after it has cured but before it has fully hardened. Takes a little experimenting to judge the best time to do this but once you have it figured out sanding and fairing will be a lot quicker and involve much less bad language.

Another hint: On flat or moderately curved surfaces I sometimes use a small flat block of wood no more than about 2"-3" square and about 1" thick as a sanding block. With finer sandpaper wrapped around, it is small enough to have complete control but just large enough to fair edges nicely.

Finish with a high build surface primer and prep for paint.

Best of luck with it.

Clive Whittfield
Auckland
New Zealand

 

[woodmanrog]

I use automotive featherfill for doing my final work filling pin holes or small edge seams. I have had very good luck and the products work right out of the tube with no mixing. final sand with 400-600 grit wet and get a perfect finish for priming.

 

[crabandy]

I would guess it's technique, I thought the West Systems faired out very well. I'm assuming you would have the same "step off" issue with Rage.

First are you spreading the filler over a large enough area? For the inlets I had to cut parts of the inlets off, tape up one half of the cowling, and re-glass the inlet to get the right shape. Then spread filler over the entire inlet extending 4-5 inches out of the inlets. I Sanded the inlets with an extra bellcrank to aileron tube (3/8 ? inch diameter) with 80 grit glued to it. Take the tube and sand 90* against the longitudinal axis of the tube at random angles to the curves on the inlet. Repeat fill and sand several times.

I also bought a Durablock set of sanding blocks that I like for the larger flatter surfaces, as well as a some smaller 3m flexible rubber sanding blocks for curves, and the tubes for the tighter radius. My auto paint store has sand paper with sticky backing that seems to work better than using contact adhesive.

 

[RV Jerry]

I have used rage for many years on many airplanes (RV types) with very good success.