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Author Topic: how do you attach the mylar covering  (Read 997 times)
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fredtq2
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« on: February 04, 2015, 09:27:22 AM »

I tried the 3M77 made a real mess
what do you use to thin contact cement
how do tou apply it sparingly to the thin wood
are there other methods
thanks
Fred Q
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duration
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« Reply #1 on: February 04, 2015, 09:41:28 AM »

Fred:

I believe there are some other posts on topic--try searching "Mylar"

If 3M77 is a contact cement it should work, but it does need thinning to consistence of 50-50 dope/thinner mixture---in other words it should brush on very easily with no apparent build-up. It should take 2 to 3 coats to give balsa a very slight gloss.

It is a good idea to brush 50/50 dope on first, allow to dry, then sand with 220 or 400 grit paper. This will make surface smoother and also fill grain a bit so less adhesive is needed.

I use Velcro cement (comes in tube and can be found at fabric stores in display with other Velcro products). I dilute with MEK (do this outside) then brush on 3 coats. It is a very good idea to build a test panel first to get adhesive application and tacking iron temperature right before working on model.

Louis
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Maxout
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« Reply #2 on: February 04, 2015, 10:23:28 AM »

I use 3M77. Here's how:

Go outside to do this. Obviously first you need to get the film on a covering frame. I go outside, spray the adhesive on the covering frame, then bring it back inside and put it on the film (which is spread out on a clean and snag-free surface using clean hands). Now set the film and frame aside, pick up your flying surface, be it the wing, stab, rudder, prop... and take it outside (obviously calm weather is required). Holding the flying surface out of the way, take your can of 3M77 and spray some into the air so you can see which way it drifts. Position yourself so that your hand holding the can is upwind of the hand holding the frame. For example, since I'm right handed, I hold the can in my right hand and stand so that the wind is coming from my right. Now, spray some adhesive into the air, and move the frame through the mist of adhesive. Repeat this until you've gotten a tiny coating of adhesive on the entire frame. Obviously you'll need to reposition it in your hand so that you get adhesive on the frame where your fingers were but without getting adhesive on your hands. Check by verifying that all of the extremities of the frame are slightly sticky. Once all extremities are sticky, go back inside. Lay the frame right side up on a clean, flat surface, and make sure that if it clings to the surface anywhere (and it will), that you take a pin or stick and gently reposition it so it's not deformed in any way. Now go get your film and frame and carefully and slowly lower it onto the flying surface until all of the weight of the frame is on the table. Then come back and with clean  hands, gently push the film down around the entire perimeter of the frame and the ribs and anything else that's intended to touch the film. Now you can cut it out with a soldering iron and continue as normal.

A lot of folks have recommended various film adjusting rigs and the like which depend upon gently wicking in adhesive onto the flying surface after it's been laid atop the film. I've tried these methods and was not satisfied, especially when I found the need to get the film on good and tight (tight film--not tight enough to warp things, but tight enough to hold the correct shape and not flop about, will reward you with larger numbers on the stopwatch). I make my covering frames from 3/8x3/4" balsa, and I crinkle the film prior to spreading it out for attachment to the covering frame. You can use an extremely soft brush to spread the film out--gives very nice results and relatively even tension distribution even across large areas (10"x32", for example on my most recent build).

I suppose I need to make a video explaining how all this gets done...
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applehoney
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« Reply #3 on: February 04, 2015, 03:13:23 PM »

Sounds rather similar to covering indoor models with microfilm many decades ago.  Lift the film off onto a wire frame, let it stand and age  before lowering the wing framework onto it.

Should you ever see a cat run through one of those standing frames ... it's an experience!
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Maxout
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« Reply #4 on: February 04, 2015, 03:43:16 PM »

Should you ever see a cat run through one of those standing frames ... it's an experience!

That's the funniest thing I've heard this week!

Hmm...would almost be worth the sacrifice of the film to see that for myself. Grin
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Olbill
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« Reply #5 on: February 04, 2015, 03:57:42 PM »

Of course Joshua does it backwards from everyone else!

I used spray on my marathon flying surface building this week instead of my usual liquid application. I had 7 pieces to cover and just didn't want to take the time to do it my regular way.

If you're going to apply 3M77 with a brush as described in other posts it needs to be thinned with 10-12 to 1 with lighter fluid or naphtha. 50-50 is WAY too much 3M77.
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PeeTee
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« Reply #6 on: February 04, 2015, 05:16:25 PM »

Bill

I suspect that Louis was describing the method of applying 5+ micron mylar to outdoor FF models, not the indoor masterpieces you produce!
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kiteshark
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« Reply #7 on: February 05, 2015, 05:57:10 PM »

I also use 3M-77.  It only takes a whiff or two from several feet up to get enough droplets on the part.  But I prefer to place mine on a fan folded piece of paper on top of a sheet of newsprint.  I don't want that spray on my hand when I'm heading inside to work with film.

The other thing that I've come across is putting the film on your covering frame with lip balm.  Smear a good coat on the covering frame then apply the film.  The great thing is that you can reposition the film as much as you want.  So you can tighten it, loosen it or correct wrinkles.  Then mist your wing frame (or other surface) with 3M-77 and lay it into the film.  I love the lip balm idea!  It really works.  I use this for Mini-Sticks and EZBs.

Dave
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frash
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« Reply #8 on: February 05, 2015, 09:00:30 PM »

The fan folded paper underneath your indoor framework is very important, particularly if you spray too much 3M77. Using flat paper underneath your framework while spraying is an easy way to glue your framework down onto whatever is underneath and the end result might be a destroyed framework. You probably will only do this once!

Fred Rash
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