gosk8ing

Hey,

Im building a mold for a scale C152 fiberglass fuselage (.46 size 69" wingspan electric). Im trying to fill all the gaps in the mold so that i can shape it. Ive tried expanding foam (spray on foam) but found its a bit soft and i dont know how it would cope with expoxy resin. This is what i was planning to do...
1. shape the foam
2. fill any imperfections with a putty
3. fiberglass and sand the whole mold
4. apply mold release
5. apply fiberglass for one half of the fuselage and vaccum
6. do the same for the other side

Are there any other fillers out there that can be used in large volumes, is cheap, easy to sand/work with and gives a hardish finish???

Cheers

Aquila223

Automotive Bondo.

soarrich

My Feedback: (98)

Try 15 minute spackling from Lowes or HomeDepot, it sands just like the foam, is easy to apply, good stuff.

gosk8ing

Hey,

Just another question,
Is there any reason why i shouldnt just lay up the fiberglass on the plug, instead of making a mold??? Why do people make a mold from the plug instead of just laying up on the plug??

Cheers

Aquila223

You make a mold as you can pull as many parts from it as you like.

Glass the plug and it's a one shot deal. One decent crash and you start all over again.

gosk8ing

Hey,

I dont think you understand what im meaning. Im going to fiberglass the plug to cover the foam make it strong and puncture resistance. Then once that is done and sanded smooth, ill cover it in mold release. Then lay your fiberglasss on top, once cured, peel from the plug. Do that to each side. Then you'll have a fiberglass part the shape of the plug. Will this work???


Cheers

Aquila223

Yes but wax it till both your arms fall off then mold release then glass.

gosk8ing

Are there any disadvantages for laying the fiberglass onto the plug instead of making a mold?? The only thing i can think of, is in a mold you can draw panel lines and scale detail so when u lay the glass, the scale detail is transfered onto the glass from the mold.

diggs_74

Really the main thing is that the finish on the outside of your parts won't be very smooth and will take quite a bit of work and filler to make it look good.. That's just dead weight you're adding to make it look nice..

dreadnaut

My Feedback: (5)

Use polyurethane foam. This is the stuff that is used as base material for flower araingements. The stuff is much easier to shape than white foam, and is not desolved by polyester resin, which is the base of Bondo. If you use White foam, as I see you have started to do, glass over it with epoxy resin, then you can Bondo on top of that.

Bondo is wonderful stuff for filling those little imperfections in plugs. Get it pretty smooth with Bondo, then use catylised Automotive Primer to get it really smooth. Then paint it and polish it.

Ditto.

If you mold your fuse in a female mold, the only finish you will need is paint. If you try to moldi it over a male plug, you will find it next to impossible to get a good seam, and you will have to fill, and sand, and fill and sand several times and them maybe get a good painted finish.

gosk8ing

Hey,

i bought some polyester resin today and tried some on the foam. Like dreadnaut said, it did desolve it, but not by much. Max depth was not even 1/4" and that was with resin caked on. I did see the polyurethane foam at the shop, but because i have already used the white foam, ill try to stick to it.
Here are my 2 options:
1. Apply Bondo over the whole job and allow it to shrink, then once dried, apply more to get it to shape.
or
2. Try painting the foam before applying bondo. This will give a protection film. The expanda foam can says you can paint it, but doesnt say if you can do it once sanded.

What do u think i should do, or should i just rip it all out start over with polyurethane foam??? I prefer not to glass over with epoxy resin cause its more expensive.

CHeers

seanreit

My Feedback: (60)

Anytime you are in a situation that you are working with Fiberglass, it certainly pays to get the right tools, materials, etc, and do the job right. Half Assing this part of the hobby, almost always ends up in parts getting thrown away because you're too embarrassed to show up with such sloppy work.

I'm a penny pincher, but when I saw the light a few years ago as to how much more could be accomplished with the right materials, I invested thousands of dollars in epoxy adhesives, vacuum, release agents, Urethane Primers, paints, etc.

TeamSeacats

yep, I second that. The epoxy is a little more expensive but you will spend a whole lot more time and nearly as much money with filler trying to fill in the melted foam.

I would coat the foam with a thick layer of epoxy and phenolic microballoons and sand that to fill in the voids - probably will require two passes. Then primer with a sandable primer, paint, buff, polish, and then you have a plug ready to make a mold.

dreadnaut

My Feedback: (5)

A key thing to remember is that there is a difference between price and cost. Epoxy resin has a higher price tag, but can actualy cost less when you factor in the labor of dealing with melting foam, and trying to sculpt the basic shape with bondo. I always use epoxy resin for making molds. It is far superior to poly resin for this. If you attempt to make a female mold from poly resin, you will be dissapointed with the result. A one gallon kit of West system is about $120-$130 USD. For a project that size you will use about 1/4 or less of it. You will wind up with a mold that will produse multiple parts. A bargain indeed.

An other suggestion is that you but the fuselage aside for a while, and make plugs nad molds for the cowl and wheel pants. If you are going to make mistakes, and you will as part of the learning curve, it is better to do it on smaller parts.

I worked for a guy that convinced the company to have us work every other weekend, all the way through, instead of every saturday. I made some good money for those few months because of the double time on Sunday. This actualy cost the company less because of setup time (it was a chemical process that took 16 hours to initiate) By starting the process every other week, instead of every week, we were able to get out three extra batches of glucose-6 phosphate dihydrogenase.

I worked for another guy that thought he was saving money by hiring a machinist for $6.00/hr. I quit. The buisness went under.

gosk8ing

Hey,

Thanks for the info. I guess ill have to use epoxy.
How do you join the fuselage sides together once made. Do you just apply some fiberglass tape to the outside, cause i dont think i could get in on the inside?

Cheers...thanks for all your help guys!!!

dreadnaut

My Feedback: (5)

Join the mold with a strip of glass tape on the inside. You can get to it through the spinner opening, the back, where the rudder post goes, and through the opening for the wing saddle.

The ilustration shows the first half of the mold layed up. Once it cures, remove the parting board and lay ou the second half of the mold. Once the whole thing is cures and before removing the plug, drill holes through the flanges for aligning pins. Use a drill press so that you get these holes straigt. They are used to line up the mold halves when tou are joining the parts.

gosk8ing

Is doing is that way shown at this website good.

http://www.houstonhobbies.com/tips/c...r-fueltank.htm

In Australia I cant find epoxy gelcoat, so i bought polyester gelcoat.
The method shown in that website will mean that my mold will become very heavy, but well less it will stay straight.

Aquila223

You can paint a thin layer of pure resin (epoxy or poly) into the mold then as it becomes tacky you lay your cloth over top of it. Gelcoats are a cosmetic thing and I wouldn't bother unless you have a lot of surface detail to enhance.

Magne

Hello.
Polyester gelcoat is normally applied in a thickness of about 1mm, which means that one square meter surface area weighs more than 1 kg.
To obtain a good, light finish free from pinholes, you can spray paint a thin coat of two part paint (automotive acrylic paint or epoxy paint) into the mold.
Epoxy paint is chemically reactive for several days after application (probably about one week, depending on conditions) so there is no need to laminate at the "tacky" stage. Allowing the epoxy paint to cure first gives a better finish, with less likelihood of the fiberglass weave showing through.
If you are using acrylic paint, then one way of achieving a good bond is to allow the first coat to cure, and then apply a second, thin coat shortly before laminating. (The reason for this is that epoxy does not bond very well to cured acrylic, but acrylic bonds to itself.)

The use of "proper" two component paint is in line with what seanreit wrote above in post #12. Cheap rattlecan paints will give you surface colour, but not a good result. There is also a SIGNIFICANT risk that the single component pait will be in conflict with your release agent. Been there....

Regards,
Magne

Aquila223

I wasn't talking about using epoxy paint. I said to paint a layer of resin onto the mold. The resin tacks off (For me, West systems slow hardner) in about 2 hours. A good cure overnight, Bagged, in a hot box.

Personally I use pigments in my resin as it gives a much better result than paint.

gosk8ing

Hey,

When i was talking about using gelcoat, i was talking about using it as a tooling resin when making the mold. Thats what the website did and thought i would try it.

http://www.houstonhobbies.com/tips/c...r-fueltank.htm

Aquila223

Tooling resin is a much harder setting product suitable for high use production molds. For the dozen parts you may eventually pull from you mould I wouldn't worry about a gel coat unless you have a lot of molded panel lines, rivets etc.

seanreit

My Feedback: (60)

Tooling Resin is not necessary unless you are going to be selling many of your parts.

For in house use, every time he says "tooling resin" read that as Epoxy resin.

For the record, JR and I are good Friends and I remember the conversations we had when he was making that Tank.

Working with Tooling Resin is a Major Pain in the Ass.

I have several quarts, tried it once, and the rest of the quarts are still collecting dust.

ByLoudDesign

Bottom line is tooling resin is harder as stated, which is good for multipart mold. But there is another side to it also, tooling gel because of the inhearint hardness polishes to a HIGH glossy finish which helps the part release and puts less stress on the mold. But as mentioned this it only in play when you plan on, say half a dozen or more parts being made from the same mold. If you store it always keep it out of the sun and wax it to protect it. @ cents! LOL

dreadnaut

My Feedback: (5)

The method shown in that website is basicaly it. My method is a little different. I like to use Dry Erase marker board for the parting surface. I have been using modeling clay to seal the parting board, but am planning to use bondo on my next one (The guy in Houston is using epoxy)

The finish of the part will be no better than the finish of the mold. A surface coat is a good idea, but using epoxy will produce pinholes because bubbles form during reaction. I like to apply PVA by pouring it on and letting the excess drain off. Thining it 50:50 with purified water (Dont use Acetone!) helps it coat better. If you get bubbles in the PVA, spray it with a mist of denatured alcohol to break them.