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Old Oct 05, 2007, 04:27 PM
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Falcon, Colorado
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wing mold pva

Just wondering... I have done research into release agents used on the wing plug and parting board, and I would really like to use PVA over a carnuba wax to release the mold from the plug. I have done many fuselage molds, but never a wing mold. I use a rag soaked in PVA (thanks dl!) and it works well, but I still need to sand the insides of the mold after they are cured to make them perfect. My question is this: Have any of you tried doing the normal wax and pva, but then waxed over the top of the pva to make it really shiny? Is this a possibility or would the wax just eat through the pva?

One other question... When making a resin channel at the TE, should I just butt the TE of the plug up to a rectangular piece of wood that would run spanwise and through both top and bottom molds, which should make TE alignment that much easier, or should I let the TE of the mold "close" around the plug, then a small flat section of mold, and THEN put the resin channel.
Thanks in advance,
Jim
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Old Oct 05, 2007, 05:38 PM
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If you apply wax over the PVA, you might soften the PVA... but you will definitely peel it off as you start to buff the wax. Just don't bother. Apply lots of wax and then apply your PVA if you want to use it. Find a way that works for you to get the PVA smooth. The mold surface will only be as good as your PVA finish... but you can always sand and polish the mold once you get it off the plug.

If you want to use a resin channel, it makes the most sense to have it start immediately at the TE of the wing.

Good luck.
-David
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Old Oct 05, 2007, 07:29 PM
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I like the concept of a resin channel butting up against the TE. It then becomes a "trimming channel". That being said I have learned to live without a channel since my mold doesn't have one.

What helps ENORMOUSLY is the use of a big cutting mat and a template to cut your wet out cloth sandwiched between wax paper. If you haven't seen the video of the German F5B build, you should check it out--I learned ALOT from it:

http://video.google.com/videoplay?do...62&q=f5b&hl=en
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Old Oct 05, 2007, 10:28 PM
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Quote:
Originally Posted by Ward Hagaman
What helps ENORMOUSLY is the use of a big cutting mat and a template to cut your wet out cloth sandwiched between wax paper.
Ditto... with one important exception. Don't use waxed paper because you can get transfer of the wax to your laminate, which is not good for adhesion. Use polyethylene sheet instead (plastic drop cloths from Home Depot or Lowes).
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Old Oct 05, 2007, 10:35 PM
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In theorey I see your point, David--haven't seen it in practice yet. But waxed paper is so darn convenient! I wonder if there is any polyethylene on a roll?
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Old Oct 05, 2007, 10:59 PM
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Ive been using depron with 4 mil Lowe's drop cloth for templates on bagged wings for a while.. Makes it 100 times easer... Ive thought about laying up outside the mold, but is it necessary? It seems kinda wasteful in the carbon department.
As for the pva, I am at the point where I don't care about a little roughness in the finish... Making wing plugs out of bagged wings SUCKS! It goes like this... Bag a wing, take it out and say," Wow.. that looks great!" Then you wet sand it down to 1000 grit and look at the reflection and notice a small "wave" from imperfect mylars, SO, prime the wings, wetsand, prime, wetsand, then put a surface coat on and here come the pinholes.. So, use a little pinhole filler, and it eats the primer and makes small "cracks", so you fix all that and begin to think that CNCing a set of plugs isnt all that expensive! Atleast they are straight at the moment, so the TE partline should not be to incredibly hard to do..

It's funny... At one point about 2 weeks ago, I said to myself, "$700 is sure a lot to pay for a molded plane." hmmm...
Thanks for the help, If there are any other tips you guys have, I would love to hear them!
Jim
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Old Oct 05, 2007, 11:49 PM
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What I use is an 1/8" mdf template. With the template to guide the roller cutter so that you end up with a net size, wet out cloth piece, perfect every time, with no extra to trim later. Its like having pre-preg to lay completely inside the wing mold with nothing hanging out or holding the mold open.
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Old Oct 06, 2007, 01:19 AM
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Falcon, Colorado
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On that topic... I wonder if it is possible to use porous release film as one of the layers of poly when cutting the wet out fabric.. I was thinking of doing a surface layer of glass and carbon, letting that set up, then adding balsa as a way to keep from getting lines in the finish. Seems like you could just skip a step and have pre cut release film in the process.
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Old Oct 06, 2007, 01:37 AM
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Quote:
Originally Posted by threcixty
On that topic... I wonder if it is possible to use porous release film as one of the layers of poly when cutting the wet out fabric.. I was thinking of doing a surface layer of glass and carbon, letting that set up, then adding balsa as a way to keep from getting lines in the finish. Seems like you could just skip a step and have pre cut release film in the process.
Are you actually seeing the balsa grain imprinting in the outer surface? I've never seen that problem. Maybe seal your balsa better, or use finer grain? Or switch to Rohacel?

I suspect you'd have trouble peeling the peel-ply off your cured outer skin without also removing it from the mold accidentally. Plus, then you'd have an additional bonding operation to glue the core (balsa) to the outer skin... which means more epoxy and more weight. Unless I'm not understanding what you intend to do with the peel ply...
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Old Oct 06, 2007, 01:44 AM
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Quote:
Originally Posted by Ward Hagaman
In theorey I see your point, David--haven't seen it in practice yet. But waxed paper is so darn convenient! I wonder if there is any polyethylene on a roll?
Fair enough... Practical experience is the same for me as it is for you. I won't mix epoxy in waxed cups either though... for the same risk of contamination.

I was reading a technical paper today on secondary bonding... and it turns out even peel ply can leave a virtually un-bondable surface. Best seems to be peel ply, followed by sanding to remove the resin imprint, and finally gentle media blast to remove residual nylon or polyester (or whatever the peel ply is), and to also roughen the surface. Then you have to clean it, of course.

I use the polyethylene drop cloths... but saran wrap will work in a pinch. It tends to be clingy, however.
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Old Oct 06, 2007, 01:56 AM
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Porous release film to lay in final layer of glass

Quote:
Originally Posted by threcixty
On that topic... I wonder if it is possible to use porous release film as one of the layers of poly when cutting the wet out fabric.. I was thinking of doing a surface layer of glass and carbon, letting that set up, then adding balsa as a way to keep from getting lines in the finish. Seems like you could just skip a step and have pre cut release film in the process.
Not quite with you in understanding this...

I have only layed up two 3m f3b wings (therefore minimally experienced).

The first layup was a failure (learning curve) as the outer glass was too dry and the balsa core (not primed) released!!

The second attempt involved a few work around as I was single handedly laying up into a one piece 3m mold onto 2k paint (layup within 24hrs). I layed up the outer glass first using release film (plastic) that had lots of little holes to bleed epoxy through as the carrier into the mold and left it in place during the cure. The plastic "holey" film releases much easier than peel ply.

As the next operation I bagged in the remainding parts - core, spar and inner glass. I again used the plastic "holey" film as the carrier for the 3/4oz inner glass. The glass was wetout on the film outside of the mold. In the video mentioned earlier I believe wetting out onto blasa can cause excess epoxy to be used. I haven't tried it so have no real experience.

On topic - I have used wax and pva however a new set of molds that I have acquired has been used with wax only and this allows masking in the mold.

Re applying wax/pva to the plug yes i do this however when looking for a shiney finish I spray the PVA

cheers Jeff
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Old Oct 06, 2007, 03:32 AM
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Like Jeff said, I was thinking about using the porous release film, not peel ply, as a carrier for the wetout carbon. I would wet out carbon on a piece of poly dropcloth, then place some porous release film over the top and cut the shapes I need from this, which in turn I would place into the mold. I thought about it some more, and realized that the bleeder I placed over this would probably stick to the sides of the mold because there would not be any release film between the bleeder and the mold.

Also, what do you seal the balsa with? I am not really worried about weight, and was even thinking that I may have finally found a use for some carbon veil I have had laying around for a few years. What other options are there for core material? Can you use fabric only? Out here in the desert, the only place to land usually includes big friggen rocks with sharp edges. I want a really ding-proof wing!
Thanks again,
Jim
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Old Oct 06, 2007, 04:46 AM
working to the closest cm
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brisbane australia
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Quote:
Originally Posted by threcixty
Like Jeff said, I was thinking about using the porous release film, not peel ply, as a carrier for the wetout carbon. ..snip..

Also, what do you seal the balsa with? .....

What other options are there for core material? ......!
Thanks again,
Jim
>using the porous release film, not peel ply, as a carrier for the wetout carbon
I used this on the outer layer of glass - this would be OK with the carbon if you are placing the core material in later - probably stating the obvious!

>realized that the bleeder I placed over this would probably stick to the sides of the mold

I simply added some extra strips of release film around the edges.

>what do you seal the balsa with? ...some seal, some don't! Have you been through the Rocketworm thread by M Koch? (in the stickies) some discussion of this -

I made a couple of F3D wings and used dope to seal the balsa -works but warps the balsa! I have even read of people using hairspray!

On my successful 3m wing I scrapped on then scrapped off a thickened mix of epoxy and flock(west product) added minimal weight and primed the wood for gluing to the precured skins ---- long way to go about doing it!


>What other options are there for core material?
I have seen balsa.....specialist cores (herex/airex) , klegacel and even (club f3b models) corogated cardboard! On slope wings where weight isn't an issue I seen refence to a thick slurry of microballooons on top of the carbon skin.

cheers jeff
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