Fitz21

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I have two plastic wing moldings that that attach to the center LE and center TE of the wing. Nothing more than cosmetic to have a nice flow from fuse to wing. The plastic is very thin and I am considering re-enforcing it with glass. I would like to keep the original plastic parts as spares, because they are a high failure item. Is there any way to build them up with glass and then remove the plastic molding? IS there some sort of releasing agent available? I have obviously not done this before and the plane also came with plastic wing tips which I carved out of wood. I do not want to carve the moldings out of wood, do to too many angles, corners, etc.. any help would be appreciated.

davidfee

You should be able to make fiberglass moldings using your plastic original pieces. The mold release can be as simple as car wax... doesn't need to be anything fancy. Plain old carnauba works great. Make sure to wax the parts at least 4 or 5 times so you get a good even coating and a nice gloss finish. Then lay up the glass using some good slow-cure finishing/laminating epoxy. There are some available at the LHS, like Zap/Pacer Z-poxy finishing resin, NHP Clear-n-Simple finishing resin... etc. Don't use something like 5-minute. 30-minute might be ok, depending on the brand, but you really want the lower viscosity and slower cure of a finishing/laminating resin.

Good luck!
-David

Fitz21

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THANKS! I figured it would be something simple. I use zpoxy with 3/4 0z cloth. would you thin with denatured alcohol to make it easier to apply? will it eat the wax if i thin it?

davidfee

I would not thin the epoxy with anything... alcohol will certainly dissolve the wax barrier. If the epoxy is too thick and doesn't wet out the glass easily, then you can heat it gently with a hairdrier or heat gun. The warm epoxy will flow better. Test it out on some scraps first to get the feel for it.

Good luck,
David

yobeekster

Since this is the topic of epoxy, I wonder what I would use to toughen and smoothen the wings if they were made out of high density foam (pink stuff from home depot). Kinda new at this!

gjs

Are these plastic parts stiff enough that they won't warp while cureing?

gjs

Toughen and smooth sound like you just want to skin with resin. Done that and it's ugly if you don't put something like a sheet of siran wrap over it to help smooth it out. Try it on some scrap, see if you like it. I'd use a real thin epoxy, like FinishCure.

Keep your wing staight while curing, it will stiffen it some and set in any twist, which a heat gun could probably remedy but why chance it. Hope this helps!

LesUyeda

If you make a mold out of plaster of paris, then fiberglass into the plaster of paris mold, you will end up as smooth as the original.

Les

Fitz21

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are you talking about using plaster to make a mold using the plastic parts or foam parts or both?

I like the plaster idea, so if this is a better way to go then using wax as the releasing agent and the original part as the mold, then what is used to release the glass part from the plaster mold?
Will it really provide a better glassed part?

LesUyeda

Make a female plaster mold from the plastic parts. You will still have to wax the plaster mold very well for release, but the finish surface will be as smooth as the plastic was. The advantage is that the plaster will be stiff enough not to move around while you are laying up.

Les

Fitz21

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I have completed the plaster mold. I am assuming That i wax the mold with carnuba and then build up the glass. Is this correct? Also, how many layers of cloth and what kind? The part i am making is no a load bearing part, I just need it stronger than the flimsy plastic of the original part. Will Zpoxy be a good choice?

Lightfoot

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I have a set of plaster of paris molds made from a plastic cowling. I have not attempted to make parts from it yet. I would think that the plaster of paris would need to be sprayed with something like polyurethane due to the porosity. It seems that it would be much easier to wax if it were sealed.

Ed Smith

If you have plaster of Paris molds then they must be sealed before. waxing. Shellac or as you say, clear polyurethane will do it. If the mold is not sealed first, lumps of plaster will come out with the part.

Ed S

Fitz21

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so, once sealed then wax and lay glass? what is your recommendation on cloth and # of layers.

Ed Smith

I have some cloth that is 2 oz cloth. It is a very close weave, I think it is refered to as "Aircraft grade" maybe even "Crowsfoot". I am a litle hazy about the proper description. I lay the 2oz. in first, the close weave will prevent pinholes and then a layer of 6oz. to give the part some body.

Ed S

Fitz21

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do you use wax as a releasing agent? Ia ready to glass and i do not want to mess things up. any last words of wisdom?

CoosBayLumber

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As Les mentioned, I too have made several fiberglass copies using the Plaster of Paris mould technique. It is a non-heat generating method, which will not warp cheap plastic originals, and based upon the cost of a sack and tap water, it is low cost materials.

I cut the fuselage in half, then glued it to a big portion of formica counter top. Built a box of 1 by 2 and screwed it onto the countertop around the fuselage half. Then poured a soupy mixture of the plaster into the box. Since it was so thick (1/2 to 1.5" in areas), the plaster mould had enough strength to be rigid for years to come.

The plaster when wet, picks up all details, but takes all night to set hard. I scratched in panel lines into the soft plastic, and using a Koh-i-noor pen then dotted ink spots along those edges which represented rivets. All of this showed up in the mould, which also showed up in the final finished fiberglass product. As the plaster creeps everywhere, it also makes a nice 90 degree edge at the join line, good for trimming the excess fiberglass cloth off later.

The hardened plaster needs a spray coating, as otherwise the multiple wax release layers just cut into the surface, making a lumpy-bumpy result upon polishing. The coating needs to be resistant to the type of binder used with the cloth.


Wm.

SKYPYRO

All I can say is Wax, wax, wax, wax, wax and PVA, PVA. After my mold has cured and then some, I pull whatever is hanging out away from the mold, and put a squirt of water all around it. The part will almost fall out, and the PVA can be removed from the part by a quick rinse under the sink. Don't ask me where to get the PVA, I got a huge jug from someone getting out of the hobby. [8D]
Dan

Fitz21

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I understand the wax, wax, wax.....what is PVA? You stated you do not know where to get some, is it some kind of releasing agent? is anything else available as a substitute?
Do I really need this PVA? Any help from anyone reviewing this post would be appreciated. Like stated earlier in the thread, I am ready to make this part. Here is what i have learned and completed so far:
1. I waxed the plastic part.
2. Created a female mold using plaster of paris.
3. Sealed the mold with polyurathane.
4. obtained various fiberglass cloth and Z-Poxy.
5. Waxed the mold with carnuba.

Ed Smith

PVA is Poly-Vinyl-Alcohol. It is another release agent. It looks like green water. It is brushed, sprayed or sponged in to the mold and allowed to dry. It forms a thin film on the mold surface. It is not essential that it is used. I use it when I cannot get a wax polish into a tight corner. I brush the PVA in instead.

Any fibre-glass products supply store should carry it. When molding always use the proper materials. You may get away with substitutes, more often you will end up with parts stuck in the mold.

Ed S

Fitz21

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Thanks for the info. I found PVA available at this site for $7.95. this site has everything one would need for making molds etc...

http://www.factor2.com/catalog/a-801...a__1318519.htm

Jeff Wohlt

I found purple PVA at my local Hobby Lobby Crafts store. Worked great. Youmay not need it after waxing but it still helps protect you mold. Spraying is the best but I have brushed it and it went down just fine.

Fitz21

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Finally! Made my glass part. After sanding, priming and painting, the part will last alot longer and i still have the mold i case i need to make another part.

Just wanted to say thanks to all the input. Couldnt have done it without this thread. Anyone trying to make a mold and glass a part: This process works!!!!

once again,thanks to everyone!!!