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C152 mold - 10/1/2007 9:58:27 AM   
gosk8ing


 

Posts: 204
Joined: 5/15/2006
From: Melbourne, AUSTRALIA
Status: offline 		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


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RE: C152 mold - 10/1/2007 11:05:59 AM   
Aquila223


 

Posts: 61
Joined: 4/1/2007
From: ChristchurchCanterbury, NEW ZEALAND
Status: offline 		Automotive Bondo.

(in reply to gosk8ing)
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RE: C152 mold - 10/1/2007 11:41:51 AM   
soarrich



Posts: 2345
Joined: 2/1/2002
From: Middletown, NJ, USA
Status: offline 		Try 15 minute spackling from Lowes or HomeDepot, it sands just like the foam, is easy to apply, good stuff.

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RE: C152 mold - 10/1/2007 11:57:08 PM   
gosk8ing


 

Posts: 204
Joined: 5/15/2006
From: Melbourne, AUSTRALIA
Status: offline 		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

(in reply to soarrich)
       Post #: 4

RE: C152 mold - 10/2/2007 9:16:28 AM   
Aquila223


 

Posts: 61
Joined: 4/1/2007
From: ChristchurchCanterbury, NEW ZEALAND
Status: offline 		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.

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RE: C152 mold - 10/2/2007 9:27:41 AM   
gosk8ing


 

Posts: 204
Joined: 5/15/2006
From: Melbourne, AUSTRALIA
Status: offline 		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

(in reply to Aquila223)
       Post #: 6

RE: C152 mold - 10/2/2007 9:29:53 AM   
Aquila223


 

Posts: 61
Joined: 4/1/2007
From: ChristchurchCanterbury, NEW ZEALAND
Status: offline 		Yes but wax it till both your arms fall off then mold release then glass.

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RE: C152 mold - 10/2/2007 11:57:41 AM   
gosk8ing


 

Posts: 204
Joined: 5/15/2006
From: Melbourne, AUSTRALIA
Status: offline 		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.

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RE: C152 mold - 10/2/2007 2:47:21 PM   
diggs_74



Posts: 1268
Joined: 1/20/2004
From: Emerald, WI, USA
Status: offline 		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..


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RE: C152 mold - 10/2/2007 4:53:18 PM   
dreadnaut



Posts: 636
Joined: 3/13/2004
From: Vista, CA, USA
Status: offline 		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.

quote:


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.



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.

< Message edited by dreadnaut -- 10/2/2007 5:01:12 PM >

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RE: C152 mold - 10/3/2007 7:08:20 AM   
gosk8ing


 

Posts: 204
Joined: 5/15/2006
From: Melbourne, AUSTRALIA
Status: offline 		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

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< Message edited by gosk8ing -- 10/3/2007 7:13:44 AM >

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RE: C152 mold - 10/3/2007 1:44:01 PM   
seanreit



Posts: 6643
Joined: 4/17/2002
From: Cedar Park, TX, USA
Status: offline 		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.

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RE: C152 mold - 10/3/2007 3:41:41 PM   
TeamSeacats



Posts: 157
Joined: 3/9/2007
From: Greenville, SC, USA
Status: offline 		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.

< Message edited by TeamSeacats -- 10/3/2007 3:43:31 PM >

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RE: C152 mold - 10/3/2007 10:08:24 PM   
dreadnaut



Posts: 636
Joined: 3/13/2004
From: Vista, CA, USA
Status: offline
quote:

ORIGINAL: gosk8ing

I prefer not to glass over with epoxy resin cause its more expensive.

CHeers


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.

(in reply to gosk8ing)