(09-05-2012, 12:59 PM)robair Wrote: Interesting Mick
Your technique is different to mine. I completely wet the silk with distilled water, apply a very thin coat of dope/thinner to the surface to be covered then lay down and tack. I then let it all dry, a spray mist bottle is used to re-wet sections that may by drying out faster than others, this stops excessive warping. When all is good and dry I recoat with a slightly thicker mixture of dope and thinners, let it dry, then repeat.
Cheers
Rob B
Sorry, I may not have been too clear on my previous post, it was 3am and I'd just gotton out of bed and wrote the reply while drinking my coffee getting ready to head off to work..
I use a 50/50 mix of Dope/thinner for all steps. I could prob make different mixtures for different steps, but that involves having more spare jars than I currently have available.
First I prep the part to be covered by giving it a light sand, then coat all the places where the silk touches the wood with a coat of dope and let it dry. Next, give it another light sand then another coat of dope and again let it dry.
Next, I soak the silk in warm water and drape it over the part to be covered. Next, using a thin brush and my thumb or finger, run a line of dope over the silk where it touches the wood. While it's still wet, "massage" it in until it soaks through the silk and adhears to the wood. usually this means running my finger/thumb up and down the "join" a few times. For the larger parts, like the fuse and the wing, I use a spray bottle with a fine mist to just give it a quick squirt where the water is starting to dry to keep it damp until I'm finished.
Once all the silk has been "glued" down, I set it aside to dry. I place a couple of weights on it just to make sure it keeps it's shape. The silk does shrink as it dries, but it doesn't shrink tight enough I don't think. I generally let it go for a couple of hours or overnight.
Next, I then coat the entire part with the dope again and set aside to dry, again with the weights on it to keep it in shape. I then leave the whole thing for a couple of days to finish drying and shrinking.
It took me several tries to develope the above method, including covering the Rudder, Vertical Stabiliser, Horizontal Stabilizer and the 2 seperate elevator parts. The above mention method was used to cover the airelons, Fuse and the wing (only half done at the moment) and it seems to be working ok.
The BEM silk I think is an artificial fabric which is maybe why it doesn't act exactly the same way as real silk or tissue does in terms of the shrinking etc. I'm reasonably certain it's the acetone that does most of the shrinking on the BEM silk instead of the water, as I noticed when I was using the Dope/Acetone mix, I was getting mega shrinkage/warpage on my test peices, while the dope/thinner mix also shrinks, but nowhere near as much due to the smaller acetone content...
Disclaimer:
The above is all speculation on my part due to what I've learned by experimentation and observation. It maybe completely wrong and have no resemblace whatsoever to reality.
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